PROPERTIES OF FIBER REINFORCED CONCRETE WITH LATEX

PROPERTIES OF FIBER REINFORCED C O N C R E T E WITH L A T E X MODIFICATION

by

HANFENG XU

B.Sc.(Polymer Science), Nanjing University of Tech., Nanjing, China, 1988

M.Tech.(Polymer Sci. and Eng.), East China University of Sci. and Tech., Shanghai, China, 1991

A THESIS S U B M I T T E D IN P A R T I A L F U L F I L M E N T OF T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF

M A S T E R OF A P P L I E D S C I E N C E

in

T H E F A C U L T Y OF G R A D U A T E S T U D I E S Department of C iv i l Engineering

We accept this thesis as conforming tq,the required standard

THE U N I V E R S I T Y OF B R I T I S H COLUMBIA

October, 2003

® Hanfeng Xu, 2003

In presenting this thesis in partial fulfillment of the requirements for an advanced degree

at the University of Brit ish Columbia, I agree that the Library shall make it freely

available for reference and study. I further agree that permission for extensive copying of

this thesis for scholarly purposes may be granted by the head of my department or by his

or her representatives. It is understood that copying or publication of this thesis for

financial gain shall not be allowed without my written permission.

Department of C i v i l Engineering

The University of Brit ish Columbia

Vancouver, Canada

October 6, 2003

Abstract

Polymer modified cement-based materials and fiber reinforced cementitious

composites are both widely used in c iv i l engineering applications. Both show great

advantages, especially in repair and rehabilitation. The work reported here, however, deals

with polymer modified fiber reinforced cement based composites ( P M - F R C ) , that is, the

combined use of fibers and polymers in the same system.

Although they have excellent bonding properties and durability, the relatively low

toughness of polymer-modified concretes is still a concern for practical applications under

seismic loading or severe service condition, especially for high strength concrete. In this

research project, a commercial styrene butadiene latex was used to produce a concrete

matrix with a compressive strength ranging from 70 to 80 M P a ; a deformed steel fiber and

two synthetic fibers (a polypropylene fiber and a blended polypropylene-polyethylene

fiber), were incorporated in the matrix to optimize a high performance concrete in terms of

flexural toughness. The results show that the high strength concrete made with latex (HS-

P M C ) still failed in a brittle manner, although some ductility was observed. Synergistic

effects between the fibers and the latex were observed in most of the composites over a

wide range of deflections, as long as suitable polymer dosages were used. However, steel

fibers appeared to be more compatible with the latex modified concrete in terms of both

load-carrying capacity and toughness. The effects of fiber content and latex dosage are

discussed, based on the results of analyses of toughness tests carried out according to

A S T M C1018 and J S C E SF4, as wel l as the post-crack strength (PCS) procedure. It is

concluded t hat a h igh p erformance composite w ith s teel fibers a nd p olymers c ould b e a

promising material for both structural and repair purposes.

Key words: flexural toughness, polymer (latex), fiber reinforced concrete (FRC) ; polymer-

modified concrete (PMC) , steel fibers, synthetic fibers, bond

11

TABLE OF CONTENTS

ABSTRACT II

TABLE OF CONTENTS I l l

LIST OF TABLES V

LIST OF FIGURES VI

LIST OF SYMBOLS OR ABBREVIATIONS XIII

ACKNOWLEDGEMENTS XIV

CHAPTER 1 INTRODUCTION 1

1.1 Polymers i n c o n c r e t e 1 1.2 F i b e r r e i n f o r c e d c o n c r e t e (FRC) 2 1.3 PM-FRC and i t s r e s e a r c h i m p o r t a n c e 3 1.4 Scope o f t h e r e s e a r c h 4 1.5 O r g a n i z a t i o n o f t h e t h e s i s 5

CHAPTER 2 LITERATURE REVIEW 6

2.1 P r i n c i p l e o f PMC and FRC 6 2.2 C o n c r e t e w i t h f i b e r r e i n f o r c e m e n t .10 2.3 Polymer m o d i f i e d f i b e r r e i n f o r c e d c o n c r e t e 11 2.4 Summary . . . . . .26

CHAPTER 3 OBJECTIVE AND SIGNIFICANCE OF THE RESEARCH . . . . 28

CHAPTER 4 EXPERIMENTAL WORK 3 0

4.1 M a t e r i a l s 30 4.2 Mix p r o p o r t i o n s 35 4.3 E x p e r i m e n t a l program 3 6 4.4 Test methods 36 4.5 F l e x u r a l toughness a n a l y s i s 41

i i i

CHAPTER 5 RESULTS 4 5

5.1 Op t i m i z a t i o n of mix design f o r high s t r e n g t h PMC . . . 45 5.2 Results f o r composite with polymer and(or) f i b e r s . . . 55

CHAPTER 6 DISCUSSION 85

6.1 Fresh concrete 85 6.2 Hardened concrete 90

6.2.1 E f f e c t s of c u r i n g method on compressive s t r e n g t h of PM-HSC 90

6.2.2 Compressive strength of l a t e x modified composites 91

6.2.3 Damage p a t t e r n of concrete c y l i n d e r s under compression 94

6.2.4 E l a s t i c Modulus and water absorption . 96 6.2.5 F l e x u r a l p r o p e r t i e s . . . . . . . . . • 99

6.2.5.1 Polymer modified concrete (PMC) 99 6.2.5.2 E f f e c t s of polymer a d d i t i o n s on FRC . . .101 6.2.5.3 E f f e c t s of f i b e r volume

i n the PMC system 119 6.2.5.4 E f f e c t s of f i b e r types 131 6.2.5.5 Combined e f f e c t s of f i b e r s and polymers .141 6.2.5.6 Hybrid macro-fiber systems i n high strength

concrete and PM-HSC 146

CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK..153

REFERENCES 157

I V

List of Tables

Table 1.1 Application of Various Fibers in Cement Products 3

Table 4.1 General properties of fibers used in the program 32

Table 4.2 Basic properties of the latex 34

Table 4.3 Basic properties of antifoamer 34

Table 4.4 Mix proportions selected for further study 35

Table 4.5 Test program 37

Table 5.1 Effect of antifoamer on workability of PMC 46

Table 5.2 Workability of polymer modified concrete (w/c =0.28) 47

Table 5.3 Effects of chemical admixture on workability of P M C 49

Table 5.4 Compressive strength of P M C for different curing methods 50

Table 5.5 Time dependence of compressive strength of P M C 50

Table 5.6 Elastic modulus of high strength concrete with polymer 51

Table 5.7 Water absorption of polymer modified concrete 51

Table 5.8 Results of workability tests 56

Table 5.9 Admixture dosages 57

Table 5.10 Density of fresh and hardened concrete 59

Table 5.11 Compressive strengths 60

Table 5.12 Flexural toughness parameters, A S T M C 1018 and JSCE-SF4 63

Table 5.13 Average M O R and PCS values for different mixes 66

Table 6.1 Concrete compressive strength 96

Table 6.3 Flexural properties of P M C 99

Table 6.4 Ratio of TFPM-FRCO.5 to TF F R C i .o (JSCE SF-4) 127

Table 6.5 Toughness improvement due to fibers 129

Table 6.6 Synergy analysis of toughness factor (JSCE-SF4) for polymer

modification and fiber reinforcement 143

v

List of Figures

Figure 2.1 Model of formation of polymer-cement co-matrix 8

Figure 2.2 Electron micrographs of (a) plain concrete and (b) latex-modified concrete 9

Figure 2.3 Secondary electron image of a cement paste with 10% of a styrene-butadiene

Copolymer 9

Figure 2.4 Impact resistance of mortar by addition of polymer (Drop height of steel

ball at failure) 16

Figure 2.5 Effects of polymer and steel fiber on impact resistance of concrete 17

Figure 2.6 Impact resistance (ratio of dynamic/static strength) of different types

of concrete 17

Figure 2.7 Effects of polymer and fiber on the bond strength between old concrete

and P M - F R M (direct tensile method) 24

Figure 4.1 Photograph of Steel Fibers 31

Figure 4.2 Photograph of PPN Fibers 31

Figure 4.3 Photograph of HPP Fibers 31

Figure 4.4 Photograph of PPN Fibers after Mixing (washed out of the mix) 31

Figure 4.5 Test Setup for Measuring Modulus of Elasticity of P M C 39

Figure 4.6 Setup of flexural Test (with data acquisition system) 40

Figure 4.7 Arrangement of "Japanese" Yoke and LVDTs for Flexural Test. 40

Figure 4.8 Schematic Description of the Flexural Toughness according to

ASTMC1018Method 42

Figure 4.9 Schematic Description of Flexural Toughness Factor of JSCE-SF4 Method 43

Figure 4.10 Schematic Description of Flexural Toughness of the Post

Crack Strength (PCS) Method 44

Figure 5.1 Appearance of P M C with 5% Latex 48

Figure 5.2 Appearance of P M C with 10% Latex 48

Figure 5.3 Appearance of P M C with 15% Latex (a) after mixing (b) after slump test 48

Figure 5.4 Load-deflection curve of concrete under compression (Plain/PMCO) 53

Figure 5.5 Load-deflection curve of concrete in compression (PMC05) 53

Figure 5.6 Load-deflection curve of concrete in compression (PMC10) 54

Figure 5.7 Load-deflection curve of concrete in compression (PMC 15) 54

v i

Figure 5.8 The Modification of load-deflection curve in flexural

toughness calculating 62

Figure 5.9 Load-deflection response of beams without polymer and fiber(mix#l Plain) 69

Figure 5.10 Load-deflection response of beams with 5% of latex (mix#2 PMC5) 69

Figure 5.11 Load-deflection response of beams with 10% of latex (mix#3 P M C 10) 70

Figure 5.12 Load-deflection response of beams with 15% of latex (mix#4 P M C 15) 70

Figure 5.13 Load-deflection response of beams with 0.5% of steel fiber (mix #5 SFRC0.5) ...71

Figure 5.14 Load-deflection response of beams with 1.0% of steel fiber (Mix #6 SFRC1.0)...71

Figure 5.15 Load-deflection response of beams with 0.5% of HPP fiber

(Mix #7 HPPFRC0.5) 72

Figure 5.16 Load-deflection response of beams with 1.0% of HPP fibers

(Mix #8HPPFRC1.0) 72

Figure 5.17 Load-deflection response of beams with 0.5% of PPN fibers

(Mix #9 PPNFRC0.5) 73

Figure 5.18 Load-deflection response of beams with 1.0% of PPN fiber

(Mix#10PPNFRC1.0) 73

Figure 5.19 Load-deflection response of beams with 5% of latex and 0.5%

of steel fiber (Mix #11PM05-SF0.5) 74


of steel fiber (Mix #12 PM05-SF1.0) 74






of steel fiber (Mix#15 PM15-SF0.5) 76


of steel fiber (Mix# 16 PM15 -SF1.0) 76



Figure 5.26 Load-deflection response of beams with 5% of Latex and 0.5%

of HPP fiber (Mix #18 PM05-HPP0.5) 77



v i i




of HPP fiber (Mix # 21 PM10-HPP1.0) \: 79




of HPP fiber (Mix # 23 PM15-HPP1.0) 80


of PPN fiber (Mix #24 PM05-PPN0.5) 80











Figure 5.38 Load-deflection response of beams with 0.5% of steel fiber and

0.5% of PPN fiber (Mix#30 Hybrid-0.5SF+0.5PPN) 83

Figure 5.39 Load-deflection response of beams with 15% latex and hybrid

0.5% SF & P P N fiber (Mix #31 PM15--SF0.5+PPN0.5) 84

Figure 5.40 Load-deflection response of beams with 15% of latex and hybrid

1.0% SF and PPN fiber (Mix #32 PM15-SF1.0+PPN1.0) 84

Figure 6.1 Effects of polymer dosage on workability of P M C 86

Figure 6.2 Effects of superplasticizer on workability of P M C

For different polymer dosages '. 86

Figure 6.3 Workability of FRC 88

Figure 6.4 Effects of polymer on dosage of superplasticizer 88

Figure 6.5(a) Slump results of PM-FRC mixes 89

Figure 6.5(b) VeBe time for PM-FRC mixes 89

viii

Figure 6.6 Effects of curing method on compressive strength of P M C 90

Figure 6.7 Compressive strength of concrete with steel fiber and latex 92

Figure 6.8 Compressive strength of concrete with latex and HPP fiber 93

Figure 6.9 Compressive strength of concrete with latex and PPN fiber 93

Figure 6.10 P M C cylinders after failure 95

Figure 6.11 FRC cylinders after failure 95

Figure 6.12 PM-FRC cylinders after failure 95

Figure 6.13 Effects of polymer content on elastic modulus of P M C 98

Figure 6.14 Time dependence of water absorption property (wt %)

of P M C with different P/C ratio 98

Figure 6.15 Average flexural response of P M C and plain concrete 99

Figure 6.16 Effects of latex on flexural response of PM-SFRC beams (Vf=0.5%) 102

Figure 6.17 Toughness indices (ASTMC1018) of concrete with 0.5% steel fiber

and different dosages of latex 102

Figure 6.18 PCS values of beams with 0.5% steel fibers and different dosages of latex 103

Figure 6.19 JSCE toughness factor for beams with 0.5% steel fibers


Figure 6.20 Effects of latex on flexural response of P M - S F R C beams (Vf=1.0%) 104

Figure 6.21 Toughness indices (ASTMC1018) of concrete with 1.0%

steel fibers and different dosages of latex 104

Figure 6:22 PCS values of beams with 1.0% steel fibers and different dosages of latex .. ..105

Figure 6.23 JSCE toughness factors for beams with 1.0% steel fibers


Figure 6.24 Effects of latex on flexural response of PM-HPPFRC beams (Vf=0.5%) 108

Figure 6.25 Toughness indices (ASTM C1018) of concrete with

0.5% HPP fibers and different dosages of latex 108

Figure 6.26 PCS values of beams with 0.5% HPP fibers and different dosages of latex 109

Figure 6.27 JSCE toughness factor for beams with 0.5% HPP


Figure 6.28 Effects of latex on flexural response of PM-HPPFRC beams (Vf=1.0%) 110

Figure 6.29 Toughness indices (ASTMC1018) of concrete with 1.0% HPP fibers


Figure 6.30 PCS.values of beams with 1.0% HPP fibers and different dosages of latex I l l

Figure 6.31 JSCE toughness factor for beams with 1.0% HPP

ix


Figure 6.32 Effects of latex on flexural response of PM-PPNFRC beams (Vf=0.5%) 114

Figure 6.33 Toughness indices (ASTMC1018) of concrete with 0.5% PPN fibers


Figure 6.34 PCS values of beams with 0.5% PPN fibers and different dosages of latex 115

Figure 6.35 JSCE toughness factor of beams with 0.5% PPN fibers and

different dosages of latex 115

Figure 6.36 Effects of latex on flexural response of PM-PPNFRC beams (Vf=1.0%) 116

Figure 6.37 Toughness indices (ASTMC1018) of concrete with 1.0% PPN fibers


Figure 6.38 PCS values of beams with 1.0% PPN fibers and different dosages of latex 117

Figure 6.39 JSCE toughness factor for beams with 1.0% PPN fibers


Figure 6.40 Flexural responses of beams with different fiber

volume fractions (PM0-SFRC) 119


volume fractions (PM5 -SFRC) 120





Figure 6.44 Toughness factors (JSCE SF-4) of PM-FRC with different V f of steel fibers... 121

Figure 6.45 Flexural responses of beams with different fiber volume fractions

(PMO-HPPFRC) 122


(PM5-HPPFRC)...,: : 122


(PM10-HPPFRC) 123


(PM15-HPPFRC) 123

Figure 6.49 Toughness factors (JSCE SF-4) of PM-FRC with different V f of HPP fibers... 124


(PM0-PPNFRC) 124


x

(PM5-PPNFRC) 125


(PM10-PPNFRC) 125


(PM15-PPNFRC) 126

Figure 6.54 Toughness factors (JSCE SF-4) of PM-FRC with different V f of PPN fibers... 126

Figure 6.55 A23 for the PM-SF system 130

Figure 6.56 A23 for the PM-HPP system 130

Figure 6.57 A23 of the PM-PPN system 131

Figure 6.58 Effect of fiber type on flexural response (PM0-FRC0.5) 132

Figure 6.59 Effect of fiber type on PCS strength (PM0-FRC0.5) 133


Figure 6.61 Effect of fiber type on PCS strength of beams (PM0-FRC1.0) 134












Figure 6.73 Effect of fiber type on PCS strength of beams (PM15-FRC 1.0) 140

Figure 6.74 Effect of fiber type on flexural toughness (JSCE-SF4) 140

Figure 6.75 Toughness-synergy analysis of PM-FRC systems 144

Figure 6.76 Synergy analysis (three-component toughness distribution) for PM-SFRC 145

Figure 6.77 Flexural performance of HSC beams with hybrid fibers

(PM0- Hybrid 0.5SF+0.5PPN) 148

Figure 6.78 PCS for beams with Hybrid fibers (PM0-Hybrid0.5SF+0.5PPN) 148

Figure 6.79 Toughness (JSCE-SF4) of hybrid fiber reinforced concrete (PM0-FRC) 149

Figure 6.80 Effects of polymer addition on load-deflection response

of beams with hybrid fibers 149

xi

Figure 6.81 Effects of polymer on PCS of beams with hybrid fibers

(PM15-HybridSF0.5+PPN0.5) 150

Figure 6.82 Effects of polymer on flexural toughness (PM15-hybrid) 150

Figure 6.83 Flexural performance of beams with hybrid fibers

(PM15-hybridl.0SF+1.0PPN) 151

Figure 6.84 PCS for beams with higher volume hybrid fibers (PM15-SF1.0+PPN1.0) 151

Figure 6.85 Toughness of hybrid-FRC beams with higher volume fractions (JSCE-SF4) 152

x i i

List of symbols or Abbreviations

P M C / M polymer-modified concrete/mortar

F R C / M fiber-reinforced concrete/mortar

P C polymer concrete

PIC polymer impregnated concrete

P M - F R C polymer modified fiber-reinforced composite (concrete or mortar)

S B R styrene-butadiene rubber

E V A ethylene-vinyl acetate

P V A poly (vinyl Acetate) fiber or powder

P A E poly-acrylic ester

EP epoxy

Name convention of P M - F R C and examples:

P M xx - w f v ) F R C zz

Polymer dosage, %

Fiber type

Fiber volume, %

PM0-SF1.0 or S F R C 1.0 material or mix containing 1.0% of steel fiber

PM5-SF C_5 material or mix containing 5% polymer with 0.5% of steel fiber

PM10-HPP 0_5 material or mix containing 10% polymer with 0.5% of H P P fiber

P M L 5 - P P N L 0 material or mix containing 15% polymer with 1.0% P P N fiber

PMIO-Hybr id (A+B) material or mix containing 10% polymer with A andB fibers

xi i i

Acknowledgements

First and foremost, I am very sincerely grateful to Dr. Sidney Mindess for his close

supervision and friendly support and encouragement. A l l these w i l l be the invaluable

foundation in my further education and future career.

Special appreciation goes to Dr. N.P. Banthia for his advices and his invaluable comments

and suggestions in reviewing of this thesis. Special thanks are due to Professor Y . Ohama

from Nihon University (Japan), for his latest reference in the area of P M C .

I also wish to express my thanks to the technicians John Wong and Max Nazar. in the C iv i l

Engineering workshop; the experimental part of this study would not have been possible

without their help. Many thanks to David Woo and Alfred Lam for their help in casting

concrete specimens.

Thanks are also extended to all my graduate colleagues and visitors, Fariborz Majdzadeh,

Ivan Duca, Kazunori Fujikake, Vivek Bingdiganavile, Rishi Gupta, Reza Soleimani, Reza

Mortazavi, Tiffany L in , and Lihe Zhang; working with them made me feel the materials lab

to be a home away from home.

Last but not least, my wife Mary Xiaoning W u and my lovely daughter, Jenny Jingyi X u

are appreciated for their love and support.

xiv

CHAPTER 1 INTRODUCTION

Their useful physical properties and relatively low cost make cement-based materials

the most widely used of c iv i l engineering materials. However, these materials have a

number of drawbacks: they are brittle, have a low failure strain, and are weak in tension.

To mitigate these problems, both polymer modification and fiber reinforcement have been

used successfully in practice. In the work reported here, the combined use of polymers and

fibers w as s tudied e xperimentally. H owever, i t i s n ecessary first t o d escribe b riefly t he

separate effects of polymers and fibers in concrete.

1.1 Polymers in concrete

Generally, there are three principal types of concrete containing polymers: polymer

impregnated concrete, polymer cement concrete and polymer concrete.

• Polymer Concrete ( P C ) — Polymer concrete is a composite containing a polymer as

the binder instead of the conventional portland cement.

* Polymer Impregnated Concrete (PIC)—PIC is generally a precast concrete, which is

dried and evacuated, and is then impregnated with a low viscosity monomer (or

mixture of monomers) that polymerize in the field to form a continuous polymer

network within the pore system. Impregnation results in markedly improved strength

and durability in comparison with conventional concrete.

o Polymer Modi f ied Concrete or Polymer Portland Cement Concrete ( P M C or P P C C ) —

Polymer cement concrete is a modified concrete in which part of the cement binder is

replaced by a synthetic organic polymer. It is produced by incorporating a monomer,

prepolymer-monomer mixture, or a dispersed polymer (latex) into a Portland cement

concrete.

Amongst these three types of polymeric materials, P M C (PPCC) is most widely used,

due to its relatively low cost, and quite similar processing technology to that of

conventional concrete.

1

Polymer latex is most commonly used in P M C . The concept of polymer latex

modified concrete is not new; 1923 saw the first patent involving natural rubber latexes

used in paving materials [1]. Synthetic latex was suggested for concrete in the early

1930's. But practical applications of P M C only became widespread in the early 1960s. B y

now, thousands of projects, such as bridge deck construction or repair, and parking garage

repairs, have been completed in North America using styrene-butadiene latex. Acryl ic

latex and epoxy polymer modifiers have also been developed and have played important

roles in repair projects.

Much research and construction experience has demonstrated that cement-based

composites with a suitable polymer latex exhibit superior bonding to old concrete and to

steel rebar, good ductility, lower permeability and better durability characteristics such as

improved resistance to freeze-thaw cycling, decreased depth of carbonation, and

reasonable chemical resistance. S B R latex* is one of the products widely used in North

America to prevent the negative effects of deicing salts. Polymer latex modified concrete

also provides increased strength and higher impact resistance.

1.2 Fiber reinforced concrete (FRC)

Fiber reinforcement is another common approach for improving the toughness of

cementitious materials. Fibers are very effective for controlling cracking, improving

ductility, and providing impact resistance, because of the way in which they bridge across

both micro-cracks and macro-cracks. Although they cannot replace the conventional steel

reinforcement used to withstand tensile and shear stresses, adding fibers to a cementitious

matrix can improve the post-cracking response as a secondary reinforcement.

Steel fibers and synthetic fibers (such as polypropylene, polyethylene, P V A and

carbon fibers) are now the most common fiber types. Their performance depends on their

elastic modulus, aspect ratio, surface texture, and also on the matrix type and the bonding

properties between the fibers and matrix. In recent years, researchers have begun to

transfer the benefits of F R C to structural applications, especially for seismic structures [2].

New developments in F R C technology have greatly extended the range of applications, as

shown in Table 1.1 [3].

* produced by Dow chemical company

2

Table 1.1 Application of Various Fibers in Cement Products

Fibre Type Application

Glass fibers Precast panels, curtain wall facings, sewer pipe, thin concrete shell

roofs, wal l plaster for concrete block.

Steel fibers

Pavement overlays, bridge decks, refractories, concrete pipe, airport

runways, pressure vessels, blast-resistant structures, tunnel linings,

ship-hull construction, cellular concrete roofing units,

Polypropylene,

Nylon fibers

Foundation piles, pre-stressed piles, facing panels, flotation units for

walkways and moorings in marinas, road-patching material,

heavyweight coatings for underwater pipe.

Asbestos fibers Sheet, pipe, boards, fireproofing and insulating materials, sewer pipes,

corrugated and flat roofing sheets, wall l ining.

Carbon fibers Corrugated units for floor construction, single and double curvature

membrane structures, boat hulls, scaffold boards.

1.3 P M - F R C and its research importance

A full understanding of the combined use of fibers and polymers in one system ( P M -

F R C ) is still not available. Progress in the area of P M - F R C has been fairly slow, partly

due to the high material cost which may discourage industrial applications, and partly due

to the lack of experimental data on the new composites; thus, the potential high

performance of these materials has been neglected. Now, however, concretes, and

particularly high strength concrete, containing polymers and fibers are of growing interest

for the following reasons:

First, there are limitations to concrete made only with polymer or with fiber. The

much lower toughness of P M C has been recognized as one of its limitations. Surveys on

some premature failures of repairs in bridges in the U .S .A have indicated that polymer

modified decks still ran the risk of cracking, due to low toughness and also undetected

high chloride ion levels in the substrate [4].

For F R C , research [5] has shown that its durability still needs to be improved,

especially for those structures in a marine environment. A lso, while fibers can improve the

3

durability of concrete, the large surface area of the fibers tends to reduce the workability

of the fresh concrete. Fiber balling, due to fiber interlocking and poor dispersion, can also

detrimentally affect the hardened properties of concrete, which in turn wi l l reduce the

durability of the concrete. Polymer modification is one of the methods which can improve

both the properties of the fresh concrete and the hardened concrete matrix, thereby

enhancing the life span of the structure. Thus polymer modified concrete can be reinforced

by short fibers, (or fiber reinforced concrete can be modified with polymers), and a

composite with the beneficial effects of both fibers and polymers may be useful for more

extensive applications.

Second, older structures with high strength concrete w i l l require high performance

repair materials. For over two decades, high strength concrete has been widely applied in

civi l engineering structures; these structures may eventually need repair or rehabilitation

after years of service, especially those in severe environments. For durable repairs, similar

mechanical properties and good bonding between the new concrete and the old concrete

substrate are required. Polymer modified high strength concrete, with or without fiber

reinforcement, would be a good candidate material. Indeed, the application of polymer

latex together with fibers in shotcrete using the dry mix process has shown that the

polymer made it easier to disperse the fibers, and rebound was significantly reduced [6].

1.4 Scope of the research

Since there is a lack of understanding of high strength P M C itself, and even how to

provide a stable P M - H S C mix, the first objective of the present research was to optimize a

cementitious system containing polymer, and to establish stable mix proportions for

polymer modified high strength concrete (PM-HSC) .

The second, and major, objective was to study the effects of the basic mix and of the

variables of polymer-fiber composites on the workability, mechanical properties and

flexural toughness. In particular, the following questions or issues were examined

experimentally:

• To what extent can the properties of the composite be improved by the combination

of fibers and polymers, compared to single component inclusions (FRC or P M C )

4

• Can fibers and polymers work together in a synergistic way to make concrete

tougher? What works (or what does not work) in terms of flexural toughness?

To this end, one type of steel fiber and two types of synthetic fibers were combined

with polymer latex, and the resulting composite properties were determined.

1. 5 Organizat ion of the thesis

Chapter one o f this thesis gives a b rief i ntroduction t o the topic, and describes the

main objectives of the thesis. Chapter two is a literature review which gives some

background of polymer modified concrete (PMC) and fiber reinforced concrete (FRC) and

the current state of knowledge in the area of P M - F R C . Chapter three describes the specific

objective of the study. Chapter four outlines the raw materials and the scope of the

experimental work. The analytical methodology of the study, and the test setup and

instrumentations are also introduced in this chapter. In Chapter five, the test results of the

program are presented. Chapter six presents a discussion of the results. The different fiber

reinforced concretes modified with different dosages of latex are compared, and an

analysis of the synergy between fibers and latex, i f any, is carried out. Conclusions are

presented in chapter seven, along with some recommendations for future work in this area.

5

CHAPTER 2 LITERATURE REVIEW

In this Chapter, the main principles underlying the use of P M C and F R C are

introduced. The properties of P M - F R C composites are then reviewed, focusing on

mechanical p roperties a nd d urability, a s well a s t he m echanisms f or t he i mprovement o f

bond properties for typical fibers and matrices. For ease of description, the term "polymer

content" or "polymer dosage" is defined as the ratio of weight of applied polymer in the

solid phase to that of cementitious materials in the mix; "fiber volume fraction" is defined

as the ratio of fiber volume to the whole F R C volume.

2.1 Principles of P M C and F R C

2.1.1 Polymers in concrete

The use of polymers in concrete goes back many years. For instance, synthetic latex

was tested and used together with natural rubber in concrete in thel930s. Since then, the

polymer types used in concrete or cement have appeared to be quite similar, but now both

the available types and quality control have been improved. Polymers in the form of

latexes or emulsions are now a common and cost-effective method for obtaining special

properties. Polymer dispersions widely used in c iv i l engineering construction include

styrene-butadiene rubber (SBR), poly (ethylene-vinyl acetate) Latex ( E V A or V A E ) , and

poly-acrylic ester Latex (PAE) . Their chemical formulations are shown as follows:

[ - C H 2 - C H = C H - C H 2 - C H 2 - C H - ] n

S B R Latex

[ - C H 2 - C H 2 - C H 2 - C H - ] n

E V A Latex O C O C H 3

[ -CH2-CH-]n

P A E Latex O C - O R R: alkyl group

6

High-grade redispersable polymer powders have been successfully employed in

concrete since 1990, and w i l l probably play a dominant role in the future, especially for

the development of prepackaged-type products. Redispersible powders are organic

polymer powders made by spray drying aqueous emulsions. Water soluble colloids are

later added to the aqueous emulsions to improve the efficiency of the spray drying process

and to enhance the redispersion of the final product. During the spray-drying process, anti-

caking agents are added to provide free-flowing and non-agglomerating properties [7].

Once the polymer powder incorporated in a dry mortar is blended with water, the powder

particles redisperse, which means they disintegrate back into the primary particles, with a

particle size of 1 - 2 um. The degree of redispersion determines the performance of

a redispersible polymer powder in the final application.

Epoxy resin is more expensive and needs a hardener, so that it is now used only in

situations in which high strength, or good adhesion properties are needed. It is also used

directly in polymer concrete (PC, non cement-based). Although a promising new family

of epoxies without hardeners is being studied in Japan, this is still in the research stage [8].

Another reason limiting the application of epoxy resin in a P M C system is the difficulty of

emulsification in water during the manufacturing process; it is therefore not easy to

disperse the resin in concrete. A possible new source of polymers for concrete or mortar is

recycled polymers from industry, such as chemically modified P E T (poly- (ethylene

terephthalate)) [9], which are attractive for both environmental considerations and the

resulting concrete properties.

2.1.2 Mechanisms of P M C

For fresh latex modified concrete, two processes govern the effects o f latex on cement

mortar and concrete, i.e., cement hydration and latex coalescence. Generally, cement

hydration occurs first, and as the cement particles hydrate and the mixture sets and

hardens, the latex particles become concentrated in the void spaces. Wi th continuous water

removal due to cement hydration, evaporation, or both, the latex particles coalesce into a

polymer that is interwoven in the hydrated cement, giving a comatrix that coats the

aggregate particles and lines the interstitial voids. The hydration and co-matrix formation

mechanism of cement with polymers is shown in Fig. 2.1. [10]. The film-forming process

7

and co-matrix mechanism have been observed by examing the microstructure of mortars

or pastes using secondary electron imaging technology, shown in Fig.2.2 [1] and Fig.2.3

[11].

If redispersible polymers are mixed in concrete with water, the polymer powders are re-

emulsified in the modified mortar and concrete, and behave, in the same manner as

latexes, as cement modifiers.

For resin modified concrete, polymerisable low-molecular weight polymers or pre-

polymers are added in a l iquid form to mortar or concrete. The polymerization process or

cross linking is initiated in the presence of water to form a polymer phase, and

simultaneously the cement hydrates. Therefore, a co-matrix phase, similar to latex

modified concrete, is formed with a network structure of interpenetrating polymer and

cement hydrate phases. Thus, the properties of the hardened concrete or mortar are

improved in the same way as those of latex modified systems [12].

(a) Immediately after (iffi) Unhydrated cement particles

o Polymer particles

Wk Aggregates

(b) First step

(c) Second step

(d) Third step (Hardened structure)

(Interstitial spaces are water)

Mixtures of unhydrated cement particles and cement gel

(On which polymer particles deposit partially)

Mixtures of cement gel and unhydrated cement particles enveloped with a close-packed layer of polymer particles

, 3 ^ , . Cement hydrates enveloped with polymer films or memberanes

C? Entrained air

Figure 2.1 Model o f formation of polymer -cement co-matrix (Mechanism of polymer modification in concrete) [10]

8

(a) (b) Figure 2.2 Electron micrographs of (a) plain concrete

and (b)latex-modified concrete (x 12000) [1]

Figure 2.3 Secondary electron image of a cement paste with 10% styrene-butadiene copolymer dispersion, hydrated for 180 days(x l000) [ l l ]

2.1.3 Properties of P M C

P M C (or polymer modified mortar, P M M ) with latex exhibits superior bonding to old

concrete and rebar, which is very attractive for concrete repairs [1,13,14,15]. Another

advantage of P M C , compared to the unmodified concrete, is its enhanced mechanical

properties. T hough t he compressive s trength m ay b e s omewhat d ecreased, t he flexural

strength and toughness are generally higher for concretes of the same consistency.

(However, decreased strengths, both flexural and compressive, were found when the same

water/cement ratio was maintained [16]). The modulus of elasticity may be lower than that

of plain concrete because of the addition of the much softer polymer phase. For normal

strength concrete, the decrease in E is generally less than 15% [17].

The drying shrinkage of polymer-modified concrete is lower than that o f conventional

concrete, though this depends on the polymer type, polymer/cement ratio, water/cement

9

ratio, cement content and curing conditions. However, the creep of P M C is highly

temperature sensitive; it may be much more than that of ordinary concrete, while other

mechanical properties such as flexural strength and elastic modulus decrease with a

temperature increase. This temperature dependence is due to the nature of polymer, i.e. its

Tg (transition temperature) and Tm (melting point).

Much research has shown that the durability of P M C is greatly improved, due to its

lower permeability; therefore P M C is especially suitable for severe condition [6,18].

Practically, P M C is applied mainly in bridge deck overlays, road surfacing, corrosion

resistant overlays, floor toppings, and more and more often for repair and rehabilitation,

(e.g., parking garage decks). Latex modified mortar is also often used in laying bricks, in

prefabricated panels and with stone and ceramic tiles because of its excellent adhesive

properties.

2.2 Concrete with fiber reinforcement

Continuous fibers have successfully been applied in areas such as aerospace, and

permit the production of materials with "tailor-made" properties for different applications.

However, only discontinuous fibers are now used in cement-based materials. Practical

applications of F R C began in the 1960's, although experiments and patents involving fiber

composites date back to 1910. Steel, glass, and synthetic fibers (polypropylene, polyvinyl

alcohol, carbon fiber, etc.) are the main types of fibers now used .

It is known that cracks start to grow long before the failure load is reached. However,

as the loads imposed on concrete approach the failure load, cracks w i l l propagate rapidly;

fibres in concrete provide a means of arresting the crack growth. Micro-fibers can bridge

the microcracks; and macro-fibers can bridge relatively larger macrocracks. If the modulus

of elasticity o f the fibre is high with respect to that o f the concrete or mortar, the fibres

help carry the load, thereby increasing the tensile strength of the material. However,

compressive strength and modulus of elasticity are affected to a much lesser degree by the

presence of fibres [2].

Often, it is toughness that may be more important than strength. Due to the fiber pull

out and debonding processes, fibres can improve the post-crack properties ("toughness"),

considerably. Impact resistance and fracture energy of F R C are also enhanced by the

10

addition of fibers. For instance, it was found that under flexural impact loading the peak

load of steel fiber reinforced concrete was about 40% higher than that of control

specimens, while the fracture energy under impact increased by a factor of about 2.5 for

normal strength concrete and about 3.5 for high strength concrete. However, it was also

found that the improvements in peak load and fracture energy were considerably smaller

than those found under static loading conditions, which was explained due to increased

fiber rupture (rather than pullout) under impact loading [19].

The dimensional stability of F R C is superior to that of normal concrete. On the basis of

Ref. [2], the creep strain of F R C (the time-dependent deformation under a constant stress)

is generally smaller than that of normal concrete. For instance, steel-fibre-reinforced

concrete may have tensile creep values only 50 to 60 per cent of those for normal concrete.

Compressive creep values, however, may be reduced by only 10 to 20 per cent of those for

plain concrete. Fibres also reduce the drying shrinkage of concrete [3]. For instance, the

shrinkage of glass-fibre-reinforced concrete can be decreased by up to 35 per cent with the

addition of 1.5 per cent by volume of fibres.

2.3 Polymer modified fiber reinforced concrete (PM-FRC)

2.3.1 Mechanical properties of P M - F R C

2.3.1.1 Polymer modified steel fiber-reinforced concrete (PM-SFRC)

Compressive and flexural behaviour

Many types of polymers, such as E V A , S B R , poly-acrylic ester (PAE) , acrylic

copolymer (AC) and Saran S A (Dow latex 464) have been used in combination with steel

fibers. Concrete containing both steel fibers and polymers have different properties from

those containing only one component. Ohama used E V A and S B R in combination with

steel fibers in a normal strength mortar to determine the individual effects on flexural

strength [12]. In his research the flexural strength of the mortar increased both as the

polymer cement ratio increased from 0 to 20% and the volume fraction of steel fibers

increased f rom 0 t o 2 %. T he S B R w as m ore e ffective t han t he E V A 1 atex a 11 he s ame

dosage. Empir ical equations for the compressive strength and flexural strength were

developed:

a f = A a f 0 ( l +P /C) ( l -W/C) +B/(1+Vf)

11

CF c = a CTC0(1+P/C)(l+Vf) +b/( l -W/C)

where O f and a c represent the flexural and compressive strengths of P M - S F R C , P/C

represents the polymer/cement ratio, W / C is the water/cement ratio (also a variable

because in the tests the consistency was controlled), af 0 and a c o are the flexural and

compressive strengths of steel fiber reinforced concrete without polymer modification, Vf

is volume fraction of steel fibers, and the other constants are obtained from the

experiments.

Flexural toughness, (the ability of the composite to absorb energy), showed a

remarkable increase with an increase of the volume fraction of steel fibers and of the

polymer/cement ratio. After reaching the peak load, the modified mortar could resist

further deformation by both bridging and pull out effects. Increasing the volume fraction

of steel fibers was more effective than increasing the polymer/cement ratio. For the same

volume of steel fibers, P M - S F R C with the addition of S B R latex had a higher toughness

than with polymer E V A .

A study on the flexural strength of mortar with the addition of poly-acryl ester (PAE)

and steel fibers (l/d=30mm/0.5mm) showed similar tendencies. The peak load increased

with both polymer and fiber contents; the flexural toughness of the composite with 2%

fiber and 20% P A E at the onset of initial cracking, which was defined as the area under

load-deflection curve out to the deflection at peak load, was 12.5 times higher than of the

un-reinforced, unmodified concrete. However, the compressive strength showed a

decrease with increasing fiber volume, though the polymer compensated for that strength

loss by reducing the water/cement ratio required to maintain a similar slump [20].

In a comparison of three commercial polymer latexes: Saran S A (Dow latex 464),

S B R (Dow latex 460) and Acry l ic copolymer—AC (Sarafon, Israel, Seracryls 4000),

Bentur [21] showed that the different polymers had different effects for the same concrete

workability. Increases in strength of the P M - S F R C could be as much as by a factor of 4 to

5, while polymer alone or fiber alone resulted in a factor of not much greater than 2.

Specifically, in the polymer-cement ratio range of 0-30%, the compressive strength of

mortar with S A kept increasing, while F R C with S B R or A C reached maximum values at

10% and 18%, respectively. For a dosage less than 24%, the splitting tensile strength and

modulus of rupture of composites with SB and A C were higher than with S A . The strain

12

capacity of P M - S F R C s under flexural load increased when 18% of polymers were added,

about 2-3.5 times greater compared to plain F R C ; the peak load also increased. It was

suggested that the strengthening effect of the fiber with ductile polymers such as SB and

A C could be improved even more significantly.

What is more important, these studies emphasized the importance of proper anti-foamer

use. Results showed that the properties of the concrete were sensitive to defoamer type

and dosage, and that a compatibility problem may exist with different polymer latexes. In

order to obtain optimum effects, a suitable of combination of latex and defoamer must be

employed.

Studies conducted at Nihon University [22] showed that P M C could be a high

performance matrix in ferrocement products. (Ferrocements are thin sheet materials

reinforced with wires, in which it is easy for cracks to form when conventional mortar is

used as the matrix; requirements such as higher strength, less cracking, higher toughness

and better durability can be met by matrix modification using polymers, fibers or both).

Compared to plain mortar, the compressive strengths of S B R and E V A modified mortars

were enhanced with increasing polymer/cement ratio; the bond strength between the

mortar and the steel wire reinforcement was also improved. The flexural strength and first

crack stress were improved regardless of the type and volume fraction of wire

reinforcement, but the values were somewhat higher for SBR. Fracture toughness showed

the same tendency no matter what kind of wire reinforcement was used; polymer modified

ferrocement with a 20%> polymer/cement ratio attained a fracture toughness 1.5 times that

of ferroement without polymer.

Further studies of P M - F R C (cement mortars containing steel fibers and polymer SBR)

in ferrocement systems showed that first cracking loads and ultimate moment capacities

increased with an increase in the steel fiber content and polymer/cement ratio. The

toughness of the ferrocement at both first crack load and ultimate load increased with the

steel fiber content and polymer/cement ratio. The flexural load-deflection curves for

ferrocement with three different matrices, i.e., P M - S F R M (mortar with steel fiber and

polymer), carbon fiber reinforced mortar ( C F R M ) and ordinary cement mortar (OCM)

were very different. The first cracking deflection of P M - S F R M was 1.4 times that of

OCM-ferrocement but less than that of C F R M . The ultimate deflection of P M - S F R M

ferrocement was about 1.5 times that of both the C F R M and the O C M , and the

13

cost/performance ratio was reasonably balanced [23]. Even relative to polymer mortar

ferrocement (unsaturated polyester resin and styrene as a binder rather than Portland

cement) and polymer impregnated mortar-ferrocement, P M - S F R M was more effective in

controlling maximum crack width when subjected to increased flexural stress in the

ferrocement system [24].

Naaman and Al-khair i used P M - F R C to try to improve high early strength concrete

for repair purposes (compressive strength greater than 35MPa within 24 hours) [25]. They

compared different mixtures containing silica fume (11%) and latex (polymer/cement ratio

of 10%), and different types and volumes of fibers. Using steel and polypropylene fibers,

with two different fiber aspect ratios and also hybrid mixtures, they optimized a mixture

which satisfied the minimum compressive strength criterion, and showed excellent values

of modulus of rupture and toughness in bending, as well as good fatigue life in the cracked

state. What is notable about this study is that the total water/cement ratio was maintained

such that, rather than large reduction in water/cement ratio, the w/c ratio between the

control and the mixtures with additives differed by less than 0.04%. Hooked steel fibers

and latex significantly improved the load vs deflection response in flexure, and the gain in

flexural strength with time. The 28-day flexural strength increased by 15% to 30% relative

to plain F R C . The energy absorption capacity at 28 days was also better than for the group

with silica fume, which showed brittle characteristics. However, contrary to the test group

with silica fume, the 1-day flexural strength was not improved and in some situations

showed a reduction. The authors attributed these phenomena to initial wet curing, which

inhibited the performance of the polymer. Unfortunately, the specific components of the

polymer were not reported.

A site application of P M - F R M (steel fiber with polyacrylic ester emulsion (PAE) and

chloro-butadiene emulsion (CBR)) , as a super-thin coating material was carried out by Wu

et al [26]. The materials showed good performance on concrete road surfaces, which are

easily cracked and even destroyed due to non-uniform subsidence of the base. Comparison

tests showed that a steel reinforced composite modified by a P A E or C B R polymer was

much better than the other three composites tested, i.e. OC(ordinary concrete) , P M C , and

F R C . Tensile bond strength increased with polymer content from 0 to 30%, while flexural

toughness reached an optimum value at 20% polymer content. The relative toughness of

these repair materials increased more than 35 times compared to those without polymer

14

modification. Wi th this technique thousands of square meters of high-grade highway road

surface have been repaired successfully.

However, it has also been reported that the toughness of concrete ( P M - F R C ) with the

addition of polymers may decrease in the long term (180 days). Sustersic [27], in a study

on P M - F R C (0.5%, 1.0% hooked steel fiber; 0.4%, 0.6% polypropylene fiber, 10% SBR) ,

showed that toughness (ASTMC1018 method) increased only up to first crack; the energy

absorption at the peak load was much higher than that of F R C without polymer. The

subsequent decrease in toughness was attributed to the large load drop after the peak load;

the post-peak load-carrying capacity of the tested P M - F R C was lower than that of F R C .

A lso, because of the presence of polymer, the interface between the fiber and the matrix

was stronger, and fibers tended to break rather than pull out. In this test program, to

maintain similar workabilities, the water/cement ratio of the concrete with polymers in

each group was decreased from 0.42 to 0.30.

Impact strength of P M - S F R C

Polymers themselves have good impact resistance and show ductile behaviour, so it

would be anticipated that for polymer modified concrete or mortar, the impact resistance

would also be improved. Concretes with elastomers (polymers with the properties of

rubber) should show higher values than those made with more brittle thermoplastic resins.

Results of drop weight tests showed an increase in the drop height required to cause

concrete failure with an increase in polymer dosage (0 to 20%>) for mortars using SBR,

P V D C , N B R , C R , P A E , P V A C and N R polymer. For different types of S B R latexes

(mainly different in the proportions of monomers and molecular structure), differences in

impact resistance exist. F ig . 2.4 gives comparison test results for four kinds of SBR,

P V D C , N B R , C R , P A E , P V A C and N R modified mortars [12].

There is little literature on the effects of the combined use of polymer and fibers on

impact resistance. In general, while the improvements under impact loading may not be

much more significant than under static loading for steel fiber reinforced concrete, they

are often much better for polymeric fiber reinforced concrete [28]; this depends, however,

on both the fibers and matrix properties. Fujuchi et al. [20] conducted a direct flexural test

by dropping a steel ball on the mid-span of concrete beams to study the impact resistance

15

of P M - F R C with poly-acrylic ester (PAE) and steel fibers; 1.0% silicone-emulsion-type

antifoamer by weight of P A E emulsion solids was used. This study showed that both

impact strength and relative impact strength were improved with an increase of

polymer/cement ratio and steel fiber volume fraction. (The relative impact strength of the

composite was defined as the " impact strength of steel reinforced PAE-modi f ied concrete

over impact strength of un-reinforced unmodified concrete"). Fig.2.5 shows the effects of

P A E polymers and steel fibers on the impact resistance of concrete. P M - S F R C with 2.0%

fiber and 20% P A E yielded a 60-fold increase in impact strength compared to the un-

reinforced and unmodified concrete. Other properties such as direct tensile strength,

flexural strength, and toughness increased as wel l by factors o f 1.7, 2.5 and 12.5,

respectively, but the compressive strength showed a decrease when the fiber volume was

increased.

Using the Hopkinson split-bar method, Jiyrndrak et al.[29] reported only slight

improvements in impact strength and toughness with steel fiber additions. However, the

TYPEcQF MORTAR ,

Fig 2.4 Impact resistance of mortar by addition of polymer (Drop height of steel ball at failure) [12]

16

Fig 2.5 Effects of polymer and steel fiber on impact resistance of concrete [20]

dynamic properties of the concrete were greatly improved when steel fibers were used

together w ith a p olymer. T he p olymer u sed w as a n a crylic ester b ased copolymer w ith

antifoamer, and the volume of steel fibers was 1.5%. The mixtures were designed based on

a similar consistency of the fresh concrete. The strength ratios (strength under dynamic

loading to static strength) of P M - F R C were 50%, 28% and 2 1 % greater than that for plain

concrete, P M C and F R C respectively. The properties of both F R C and plain concrete were

markedly improved by the polymer, as shown in Fig. 2.6.

F ig 2.6 Impact resistance (ratio of dynamic/static strength) of different types of concrete (Note: "polymer concrete" represents polymer-modified concrete [29])

os-

1 2 3 4 5 6 . Blow, Number

17

Overall, polymer and fiber combinations appear to have great effects on the impact

resistance of cementitious materials. However, these dynamic properties depend, at least

in part, on the method of measurement employed. Because there is no commonly accepted

standard test to obtain real dynamic material properties, only relative comparisons of F R C

or P M C or P M - F R C could be made.

2.3.1.2 Polymer modified synthetic fiber reinforced concrete

With the growing interest in the use of synthetic fiber reinforced concrete in civi l

engineering, studies have been carried out on various new fibers made from polymers. The

most common types of synthetic fiber are polyethylene (PE), polypropylene (PP), acrylic

(PAN), poly (vinyl alcohol) (PVA) , polyamides (PA), polyester (PES), and carbon (CF).

However, polypropylene and carbon fibers are the two major types of fibers that have been

used in P M - F R C systems, and thus only P M - F R C with these two fibers wi l l be reviewed

in this section.

Polypropylene/polyethylene fiber ( P M - P P / P E F R O

Polypropylene (PP) fibers are currently the most commonly used synthetic fibers. They

are particularly e ffective for arresting shrinkage c racks at early a ges. PP fiber modified

cement mortars containing polymers have been suggested for repair work by Mantegazza

et al.[30] They showed that, given a minimum percentage (about 0.15%) of PP fibers and

10% of sil ica fume, optimal properties could be obtained by adding 9% of acryl acid

copolymer. Some commercial applications with this material have been made in the repair

market using a prepackaged cement binder with polypropylene fiber and redispersible

polymer [31]. High compatibility with the substrate was found for mortar with fiber and

polymer ( P M - F R M ) compared to conventional cementitious mortar (OPC), polymer

mortar (EP, epoxy resin mortar), fly ash mortar (FA) and sil ica fume mortar (SF). The

prepackaged mortar contained polymer in the range of 5-10% and suitable polypropylene

fibers. It was found that, even though the EP mortar had the lowest porosity values and the

finest pore sizes, and low drying shrinkage, P M - F R M and P M C showed outstanding

general properties for repair due to similar elastic modulus to normal concrete. The elastic

18

modulus of E P mortar was much lower than that of any of the other mortars, only 1/3 that

of the normal concrete; the elastic moduli of P M C and P M - F R M were higher compared to

concrete containing E P , and similar to that of normal concrete; therefore, they may be

more compatible with hardened concrete than is polymer mortar.

Polymer modified concrete with polypropylene fibers has been used in lightweight

concrete containing polystyrene particles. In addition to the improved adhesion properties,

the splitting tensile strength to compressive strength ratio increased with the bulk density

for densities lower than 1800 kg/m 3 [32].

PP and P E fibers are often used in P M - F R C / M together with other fibers, as a hybrid

F R C . Mixtures of polypropylene and glass fibres or, alternatively, mica flakes used as

fibres may help prevent the long-term decreases in tensile and impact strength which are

generally abserved with G F R C [3]. Ohama's study [15] on hybrids of steel and

polyethylene fibers showed that the maximum flexural load, direct tensile strength and

compressive strength of the composite were more strongly affected by polymer latex

modification than by polyethylene fiber reinforcement, and increased with increasing

polymer/cement r atio; A lso, the f lexural b ehaviour o f the c omposite a fter c racking w as

generally improved with an increase of the polyethylene fiber volume fraction (from 0 to

3%) and polymer/cement ratio (from 0 to 20% by weight of solid phase). More

importantly, the flexural toughness and maximum strain of the system were remarkably

improved with P E fibers and could be further enhanced with polymer S B R . When the fiber

volume increased, the peak load and toughness of P M - F R C increased more in the presence

of polymer than without polymer. Even when the polymer/cement ratio reached 20%, no

toughness decrease was found, due to the hybrid effects.

Soroushian et al. [33] showed that with 10% of polymer latex S B R , they could

produce a low permeability fiber concrete, even though the PP fibers themselves had no

significant effects on the chloride permeability of P M - F R C .

Carbon fibers ( P M - C F R C )

Carbon fibers are generally classified as micro-fibers due to their small diameter;

typical volume fractions range from 0.5% to 5%. Considerable gains in flexural strength

and toughness, tensile strength, impact resistance and dimensional stability can be

19

achieved. The effectiveness of carbon fibers in arresting the microcracks in the matrix is

due to the very small (or close) fiber spacing.

In recent years, the lower cost of low modulus pitch-based carbon fibers has made it

possible to consider commercial applications. Tests on polymer—SBR modified-carbon

fiber reinforced mortar carried out by Soroushian et al. [34] showed that latex

modification and carbon reinforcement could play complementary roles in the composite.

The results indicated major gains in the bond strength between carbon fibers and the

cementitious matrix resulting from latex modification. Flexural toughness was also

increased through latex modification, but the effect of latex addition on flexural strength

was relatively small. Latex modification was observed to cause reductions in the

compressive strength of C F R C composites. The impact strengths of unmodified and latex-

modified composites were comparable. In this study, to maintain similar workabilities, the

water/binder ratio of the mortar was increased from 0.306 to 0.370 after adding two kinds

of S B R ; the air content was also very high, ranging from 10% to 14%.

A similar P M - F R C system, containing pitch-based carbon fibers with S B R latex,

was optimized for repair purposes by A l i , Abdel-Zaher and Ambalavanan [35]. Results

showed the superiority of S B R latex modified carbon fiber reinforced mortars to other

mortars, in enhancing the mechanical properties of the plain mortar. The slight adverse

effect on compressive strength was not significant for repair applications. The optimum

dosage for S B R in mortar was 10%o. Increasing the amount of si l ica fume in mortar

containing S B R proportionally reduced the short-term quality of the repair mortar; the

long-term performance was not studied. A lka l i resistant glass fibers were also used in

this study and showed similar enhanced properties. The optimum dosages of fibers were

0.5 percent or 6 percent by weight of cement to S B R modified mortar, for carbon fiber and

glass fiber, respectively.

Kamel Zayat et al.[36] showed that the effect of latex on the properties of P M - C F R C

was remarkable. Four mixes with different latex-to-binder ratios (0,5,10, and 15 % SBR)

together with 2% carbon fiber were batched, with all water-binder ratios held constant at

0.42. Workability, compressive strength, flexural strength, impact resistance, and tensile

stress-strain behavior were studied. The results showed that at low dosages of S B R (less

than 10%o), the compressive strength of carbon fiber cement tended to decrease. At a 15

percent latex-binder ratio, however, the compressive strength increased significantly; latex

20

additions to carbon fiber cement significantly increased flexural strength and impact

resistance, with this effect becoming more pronounced as the latex content increased up to

15%. The numbers of blows of a drop weight machine to achieve first crack and ultimate

failure increased about 3 times compared to unmodified C F R C . A t 5% and 10% latex-

binder ratios, the tensile strengths of carbon fiber cement seemed to be unaffected, while

the tensile toughness increased due to increased tensile strain. However, at 15% latex

content, the tensile bond strength between carbon fibers and cement increased to almost

twice that of C F R C with less than 10% latex, leading to a tendency for fiber rupture rather

than fiber p ull-out. C onsequently, at h igh 1 atex-binder r atios, t ensile s trength i ncreased,

while tensile toughness showed a tendency to decrease. This phenomenon is similar to the

toughness decrease o f P M - S F R C in Ref. [37].

Cao and Chung [38], to evaluate the effects of different polymers with and without

silica fume, conducted comparison studies on polymer modified carbon fiber mortar. They

maintained the same water-cement ratio (0.35) and fiber volume (0.35%), and measured

strength and electrical resistivity. Tensile strength tests showed that the strength of each

group was enhanced, with or without silica fume. A 15% acrylic dispersion was the most

effective a dmixture f or achieving h igh t ensile d uctility and s trength, compared t o o ther

polymers such as S B R , styrene acrylic, and methylcellulose.

2.3.1.3 Polymer modified glass fiber reinforced concrete ( P M - G F R C )

The development of fibers with alkali-resistant properties has made possible the

widespread application of glass-fiber reinforced concrete ( G F R C or G R C ) . However, the

aging problems of G F R C are still not completely solved. Strength and ductility reductions

under severe condition, such as in marine areas with high chloride contents, dry and hot

weather, and seismic and cyclic loading, limit its service.

Over the years, much work has been done in trying to modify the cement matrix

(decreased a lkali c ontent i n c oncrete b y u se o f d ifferent c ements), t o r n odify t he fibers

themselves by surface treatments or surface coating, or to modify the chemistry of the

glass fibers. However the best ways of improving durability still appear to be by additions

of supplementary cementing materials and polymers. A state-of-the-art report [2] gives an

overview and the details of the mechanisms of polymer modification for glass fiber

21

reinforced concrete (Part 3.4.2). A polymer f i lm not only protects some of the individual

glass filaments from alkali attack, but also partially fills the spaces between the filaments;

therefore the embrittlement effect is reduced and the strength degradation is overcome.

Soroushian et al have shown that polymer additions can improve flexural strength and

toughness significantly: 15% polymer/cement ratio leads to 40%> increase in M O R and

more than 100% in toughness [39]. Bi j ien illustrated that the durability can be improved

remarkably by a latex admixture, as the glass fibers may be "sealed" by the polymer

particles or f i lm. Ref. [40] illustrates typical improvements in G F R C due to polymers in

dry, outdoor and wet surroundings, in terms of tensile strength retention up to 4 years.

Several effective p olymers f or m odified c oncrete o r m ortar ( G F R C / M ) had p articularly

good performance when exposed in natural weathering conditions. These were vinyl

chloride-vinyl propionate ( V C - V P ) , acrylic-styrene copolymer and acrylic polymer,

although not all of them were effective in a water-saturated state.

Long-term impact test results by Majumdar suggested that at least nine different kinds

of polymer could improve the impact performance of G F R C , though the impact strength

still decreased after one year. In this test program the volume fraction of glass fiber was

5%o and the polymer/cement ratio was 10% [41]. The Izod impact strengths of P M - G F R C

in natural weathering showed a decrease within 7 years, although much less than that of

plain G F R C . A sidewall using curtain sculpture made of ferrocement with P M - G F R C (2%

of alkali-resistant glass fiber and 10% SBR) was reported in Japan to prevent cracks and

delamination [42].

Studies on the effects of polyvinyl alcohol (PVA) powder on glass fiber-reinforced

composites are ongoing. L i et al have provided a good summary of the modifying effects

of P V A [13]. S mall a mounts o f P V A (2% b y w eight) w i l l i mprove t he b ond s trength

between the aggregate and cement paste, and the interfacial transition zone wi l l be

decreased in thickness. The P V A could also enhance the effects of steel and brass fibers

due to the formation of a ductile and fine-grained interfacial layer, which nucleates on C H

and C S H . Thus, interfacial parameters such as the interfacial fracture energy could be

improved. Microscopic analysis by means of S E M and E D A X confirmed that no damage

was found on the surface of the glass fibers. P V A powder had a tendency to migrate to the

interface and to prevent the accumulation of calcium hydroxide.

22

In summary, the improved mechanical properties and durability of P M - G F R C / M may

be partially due to a f i lm effect with a protective function on the glass fiber surface. Good

bond at the interface with the matrix, partially attributed to matrix modification by

reduction of flaws, may also reduce the occurrence of stress concentrations.

2.3.1.4 Bonding characteristics of PM-FRC

As mentioned earlier, one major reason for using polymers in concrete or mortar is

their good adhesion properties. The polymers mentioned above improve bonding

considerably both to concrete and to steel, and even to wood. The use of latex-modified

pastes as bonding agents for ordinary cement mortar or concrete substrates is a widespread

practice for trowel work. Ohama has found nearly a ten-fold increase in adhesion to

ordinary cement mortar of SBR-modif ied mortar with a polymer-cement ratio of 20%,

compared to unmodified mortar [3]. In general, the bond strength of the latex-modified

mortars to the substrate or rebar increases with an increase in the polymer-cement ratio,

and reaches a maximum at polymer-cement ratios of about 10 to 20%. Cationic latex-

modified mortars develop much higher bond strengths than unmodified, anionic or

nonionic latex-modified mortars. Such good adhesion or bond has been attributed to the

presence of electrochemically active polymer-cement co-matrices at the interfaces [8,43].

Bond strength can also be improved by fiber additions. Banthia and Dubeau [44]

carried o ut d irect t ensile t ests t o e valuate t he b ond s trength b etween b ase c oncrete and

repair mortar with carbon microfibers and steel microfibers. Tests at room temperature

showed that all failures occurred at the interface. Fiber additions enhanced bond strength,

with carbon fibers being more effective in a paste matrix and steel fibers more effective in

a mortar matrix. Chen et a l . 's research [45] o n the bond characteristics o f carbon fiber

reinforced concrete also showed a bond strength increase, up to 89% beyond the levels

achieved b y t he u se a dmixtures s uch as s i l ica fume o r 1 atex. S lant s hear b ond t ests o n

cellulose fiber modified mortar by Soroushian [46] indicated that the introduction of the

fibers (0.24%o by volume) to the mortar substantially enhanced the bond strength to a

concrete substrate and provided a highly durable bond. Shrinkage crack reduction at the

interface may explain the fiber effects on the bond properties of repair composites.

23

Polymer modification further enhances bond strength. Using a uniaxial tension test, a

study by Banthia and Y a n [47] showed that fiber reinforcement of the polymer modified

mortar further improved the bond strength and fracture energy. Micro-steel fibers were

more effective than carbon fibers; the authors attributed this gain to shrinkage reduction of

the new concrete since fibers did not cross the interface between old and new concrete. F ig

2.7 shows the effects of polymers and fibers on the bond strength. The same phenomenon

is reported in Ref.[48]: 0.5% by weight of short carbon fibers can increase by 150% the

bond s trength u nder t ension a nd b y 110% t hat under s hear b etween b ricks a nd m ortar.

However, fibers in excess of the optimum amounts gave less bond strengthening, due to

increased porosity in the mortar.

5.000

2 3.000

i

_ 2,000

1,000 0 0.02 0.04 O.Ofl 0.08 0.1 0.12 0.14

Deformation (mm)

Fig 2.7 Effects of polymer and fiber on the bond strength between old concrete and P M - F R M (direct tensile method) [47]

2.3.2 Durabi l i ty of P M - F R C

Generally, the durability of a fiber-reinforced composite depends on fiber type, mix

design and the conditions of service. A comparative study was carried out by Kosa et al.

[5] on fiber reinforced mortar using accelerated tests, in which specimens were in

continuous exposure or intermittent drying and wetting in simulated seawater maintained

at20°C and80 °C from 2 to 1 0 months. Flexural tests showed that polypropylene fiber

reinforced mortar had the best overall durability; glass fiber reinforced mortar showed the

24

poorest performance. Steel fiber reinforced mortar also showed noticeable reductions in

strength and toughness, but took 5 times longer to undergo a 20% peak strength loss than

did G F R M . For slurry infiltrated fiber concrete (SIFCON), the reductions were moderate.

It may be concluded that durability of F R C is similar or slightly better than that of

conventional concrete or mortar, and needs further modification i f F R C / M is to be applied

in severe conditions.

Numerous studies have demonstrated that polymer modified concretes or mortars

perform wel l in terms of durability. Compared to conventional concretes or mortars, P M C

has a dense micro structure and smaller discontinuous pores, a less porous transition zone,

better bond between the aggregate and the cement matrix, and bridged microcracks, all

leading to superior durability through the improvements in impermeability, watertightness,

freeze-thaw resistance, chloride diffusion, corrosion and carbonation resistance [1,18

,43,49]. From all of these effects, better durability of P M - F R C / M is to be expected. A

study of the combined effects of fibers and S B R latex on durability was conducted using

accelerated tests by Ohama [50]. His results showed that carbonation and chloride ion

penetration in the P M - F R M matrix of ferrocement decreased dramatically; To reach the

same depth of chloride ion penetration in 10mm samples with 10%> and 20%> S B R needed

about 91 days and 182 days of immersion respectively, while the control group required

only 7 days. In the same exposure period of 91'days the carbonation depths of the samples

decreased with increasing polymer-cement ratio, to only 60%> and 20%> of those for the

control group when 20%> and 10%> of S B R were incorporated, respectively. The corrosion-

inhibiting properties were also improved with an increase in polymer/cement ratio.

Rols et al.[51] showed the retention of flexural strength of polymer modified

composites in three different accelerated aging conditions: in air at 20°C and 60% relative

humidity; in water at 60 °C; and cyclic aging by drying at 60 °C and wetting at 20 °C. P M -

F R C with 5%> polymer and 1.0% of polypropylene fiber maintained ductility whatever the

aging might be, while P M - F R C with glass fibers still showed losses very quickly. S E M

observation showed that the interfaces with polyproprene fibers were densified and had

low crystallinity in the presence of vinyl and acrylic polymers; chemical degradation of

glass fibers was prevented while the physical degradation induced by crystals merging

perpendicular to the fiber weakened the material. Bi jen's study concluded that to maintain

25

a high strength and strain capacity higher polymer contents should be used. While for

indoor or dry applications the durability was acceptable, much better effects could be

achieved by using mineral admixtures such as metakaoline. So, he was able to conclude:

"polymer modified glass fiber reinforced cement: a successful composite" [52].

Experience with applications of P M - G F R M (A.R.glass fiber mortar coating for repair) in

navigation lock walls has shown relatively good durability [44].

Razl [ 53] described three practical examples o f the use o f P M - F R M i n thin repairs

(6mm), thick layers (12-18mm) and shotcrete (60~120mm), in which durability was

studied together with mechanical properties. P M - F R M with polypropylene fibers or glass

fibers and polymers for repair and rehabilitation showed improved mechanical strength

and durability. Freeze-thaw deterioration ( A S T M C666, procedure A ) was less than 1%

after 300 cycles; the rapid chloride penetration index (AASHTO-T-277 method) ranged

from 310 ~ 680 Coulombs. The salt scaling resistance of these repair layers was also

satisfactory.

Studies of mortar with carbon fibers and polymers ( P M - C F R M ) have indicated that,

even with higher water/cement ratios than the control group, latex modification could

result in reductions in water absorption, drying shrinkage, and specific gravity of C F R M .

The freeze-thaw durability and particularly the acid resistance of carbon fiber reinforced

mortar were improved in the presence of latex [34].

2.4 Summary of the l i terature review

Compared with F R C and P M C , research on cement-based composites with both

polymer modification and fiber reinforcement is relatively new. On the basis of the literature

survey, the following conclusions may be drawn:

(1) Previous work on P M - F R C has focused mainly on normal strength concrete, and a

few high early strength concretes for repair purposes; steel fibers, E V A , S B R and P A E

polymers have been studied more extensively than other fibers and polymers.

There are few reports in the literature on successful approaches to get stable high

strength P M C and P M - F R C . Related topics such as toughness and impact resistance are

not much discussed in the high strength concretes incorporating both fibers and polymers.

26

(2) The workability of P M - F R C / M is suitable for manufacture and placement.

However, air content must be carefully controlled with defoamers to ensure low air

contents.

(3) Generally, composites with a combination of fibers and polymer modification

show superior mechanical properties, toughness, and better bond strength than those with

a single modification. The extent of the composite effect depends on the polymer and

fiber types and dosages.

S B R and acryl based ( P A E or copolymer) emulsions are still the two principal kinds

of polymers widely used in repair. P V A powder is most effective in P M - G F R M .

Methycellouse is very attractive due to its low dosage and therefore low cost. However,

due to the different experimental programs carried out by the various researchers, such as

keeping either the same consistency or the same water/binder ratio, the properties

observed vary greatly, making comparisons difficult.

(4) Impact resistance of P M - F R C is enhanced. However, no fundamental material

properties could be obtained due to the limitations of test methods. Only relative

comparison are currently possible.

(5) The durability of P M - F R C is improved considerably. However, the life span of

polymer modified fiber-reinforced composites with A . R glass fibers is still questionable

for long-term repairs under saturated conditions. The sequence of durability is P M -

S N F R C > P M - S F R C » P M - G F R C for the same type of polymer modification.

(6) Due to its relatively higher cost, the application of P M - F R C is mainly in repair and

in applications such as surface coatings of highways, parking decks and bridge decks,

overlays, pavement joints, piers, and runways, where requirements such as high toughness,

waterproofing, abrasion resistance and freeze-thaw resistance must be met. Its anti-crack

and high durability properties, high compatibility with the substrate, higher toughness and

bond strength, and ease of construction make it an almost perfect material for repairs.

A lso, P M - F R C is used as a high performance matrix in ferrocement, for example, in

boats and marine structures, in housing units, water tanks, grain silos and roofing.

27

CHAPTER 3 OBJECTIVE AND SIGNIFICANCE OF THIS RESEARCH

As mentioned earlier, both polymer modified- concrete (PMC) and fiber reinforced

concrete (FRC) have many advantages over plain concrete and both have been applied in

the field. However, the combination of fibers and polymers has not been investigated

extensively. The main objective of this research is to develop very high performance

cement-based composites using polymer modification, focusing particularly on high

strength and high flexural toughness.

The target compressive strength of the polymer concrete matrix was in the range of 70

to 80MPa. To optimize the mix proportions to produce a high strength P M C matrix, the

dosage of anti-foamer and the special curing procedures needed f or high strength P M C

were studied. Other important properties, such as elastic modulus and water absorption,

which may be helpful for understanding the performance of P M - F R C with a P M C matrix,

were also studied.

In addition, the influence of various fiber and polymer combinations on the properties

of fresh concrete, such as workability and air content, and on the mechanical properties of

the hardened c oncrete, m ainly its compressive s trength, flexural strength and toughness

were studied. B y analyzing the load-deflection curves from flexural tests, the load capacity

and post- crack properties of P M - F R C were determined and the effects of polymers and

fibers in high strength concrete systems were investigated.

The possible synergy between fibers and polymers was another aspect of this

research. As is wel l known from previous research, both polymers and fibers have

considerable effects on the properties of concrete. However, the synergistic effects of

these two materials on fracture toughness have not been studied intensively. Benefits (or

synergy) of the combination of polymer and fibers, i f any, can be determined through

comparison with P M C and F R C . Therefore control groups of high strength concrete

(HSC), made only with either P M C or F R C were also tested.

It must be emphasized that, in the present research program, the water/cementitious

materials ratio was kept constant, so that the effects of the polymer could be isolated. This

28

is in contrast to the more common approach for polymer modified concrete adapted by

other researchers, to use the same consistency rather than the same w/c ratio.

In addition, in order to evaluate the performance of a new type of synthetic fiber—

poly ethylene (PE) and polypropylene (PP) blended together, a high-density polypropylene

(HPP) fiber was selected as a reference fiber for comparisons in high strength concrete

with and without polymer inclusions.

From a p ractical p oint o f v iew, i n o rder t o be m ore c ost e ffective, the a mounts o f

polymer and fiber inclusions must be controlled. The maximum polymer/cement ratio in

the P M - F R C system studied was 15% by weight and the maximum fiber volume fraction

for both polymeric fibers and steel fibers was less than 2%, and mostly less than 1%>, since

this is more reasonable economically for future practical applications. Various

combinations of polymer and fibers were studied in this project:

• One type of commercially used polymer, polystyrene-butadiene based latex

• One type of deformed steel fiber

• Two types of polymer fibers, (1) H P P and (2) a new kind of fiber which is blended

PP and P E

In this investigation, 32 different mixes were cast and examined, including 1 mix of

plain concrete, 3 mixes of P M C , 6 mixes of F R C , and 19 mixes of P M - F R C . In addition 3

mixes containing a hybrid system of macro fibers with and without latex modification

were studied.

29

CHAPTER 4 EXPERIMENTAL WORK

4.1 Materials

4.1.1 Fibers

In the present program, three different kinds of macro-fibers, all with lengths of 50mm

were used. Photographs of the fibers used in this program are shown in F ig. 4.1 to 4.3.

Steel fibers (SF)

In general, deformed fibers bring about significant improvements in toughness of

concrete. Based on a previous study [54], fibers with deformations only at the ends appear

to be more effective than those with deformation over their entire length. In this program,

an end deformed macro fiber produced by the Optimet company was used.

Polypropylene fibers (HPP)

A type of monofilament macro polymer fiber, named High Performance Polymer fiber

(or HPP fiber), was used as a reference fiber. Th is fiber is manufactured by Synthetic

Industries (SI international).

Blended poly-propylene and polv-ethvlene fibers (PPN)

P P N is a kind of macro fiber (commercially called Structural Fiber, produced by W.R.

Grace). Since it is a new type of fiber, which contains Polyethylene and Polypropylene,

the name P P N is used. Unl ike conventional fibrillated and monofilament synthetic fibers,

which are added to concrete for the control of plastic shrinkage cracking, P P N fibers are

monofilament synthetic macro-fibers, 5 0mm 1 ong, manufactured f rom a p olymer b lend.

This blending enables the monofilament fiber to fibrillate partially during mixing, thereby

increasing the bond between the fiber and the concrete matrix. A photograph of these

fibers after mixing is shown in Fig. 4.4. Properties of these three fibers are given in Table

4.1.

30

Figure 4.1 Photograph of Steel Fibers Figure 4.3 Photograph of HPP Fibers

31

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4.1.2 Polymer system

Polymer (SBR-- polystyrene-butadiene rubber)

The polymer selected in this study is a type of latex, the main component of which is

a styrene butadiene emulsion containing special admixtures. Physical properties of the

latex are shown in Table 4.2. It is designed for use as a bonding agent with concrete and

cement-based products i n both interior and exterior applications. Concretes o r mortars

have been modified by latexes with similar components, because of their excellent bond

to the substrate and improvements in resistance to penetration by chlorides and de-icing

salts (very low permeability). These properties are particularly useful for cases such as

protective mortar overlays on bridge decks, and parking garages [1]. Therefore, selection

of this polymer is practical for possible field use with newly developed composites.

Defoamer (silicone emulsion)

Dow Corning Anti foam B emulsion, a type of industrial-grade silicone emulsion, is

used to control foam in aqueous systems. This chemical was originally applied in other

industrial applications such as cooling towers, fermentation applications, detergent

solutions, and insecticides, etc., Based on its specifications, Dow Corning Antifoam B

emulsion meets the requirement for latex-concrete formulations. It is also usable over a

wide range of p H and temperature. The physical properties of the antifoamer are given in

Table 4.3.

The amount of antifoamer needed for a polymer system depends on the compatibility

of the materials. Generally, this can be determined through trials. Based on the supplier's

specification, very low concentrations should work effectively: one to 100 parts of active

silicone per mi l l ion parts foamer are sufficient to eliminate most foams. In the present

program, 50ppm active silicone was first used; this was subsequently reduced to achieve

the level of foam control desired, as discussed later in Chapter 5.

33

Table 4.2 Basic properties of the latex

Ingredient Aqueous styrene-butadiene Appearance Milky liquid

Odour slight styrene or ammonia odor Specific Gravity 1.01

p H value 8.5-10.5 Solid content 48%

Tg (glass transition 4°C temperature)

Table 4.3 Basic properties of antifoamer

Ingredient Silicone mulsion Emulsion type Non-ionic

Appearance Milky white thin liquid Suitable diluent Cool water

Specific Gravity, at 25°C 1.0 p H value 6.5

Active ingredient 10% Consistency, at 25°C, (cp) 350

4.1.3 Other raw materials

Cement: C S A type 10 normal Portland cement ( A S T M type I) was used in this

study.

Aggregate: The coarse aggregate was 10-14mm crushed stone. The fine aggregate

was clean river sand with a fineness modulus of about 2.6.

Mineral admixture: Si l ica fume meeting the requirement of A S T M C1240, from

Lafarge Canada Inc., was used in this study.

Chemical admixtures:

A superplasticizer, R H E O B U I L D 3000FC, was used to improve the workability of

the concrete as necessary. This admixture belongs to a new category of synthetic

compounds (Polycarboxylate-based) with a specific gravity of 1.087. It meets the

requirement of A S T M C494 types A and F.

34

A n air entraining agent, M B - V R (standard), was used in the mixes without polymer.

This admixture is a ready-to-use solution (NaOH alkalized vinsol resin) with a specific

gravity of 1.037.

4.2 M i x proportion study

About 20 trial mixes were cast to determine the compressive strength and workability

that could be obtained, an optimized curing method and the compatibility of the cement

and the polymer. Six cylinders were cast for each trial mix of either plain high strength

concrete or polymer modified high strength concrete. Trial tests were also done for fiber

reinforced concrete, and polymer modified fiber reinforced concrete. Adjustments were

made in the chemical admixture dosages to achieve the required workability and

compressive strength. The final mix proportions selected for this program are shown in

Table 4.4. The processes followed for the trial tests for optimization purposes, including

some of other properties of fresh concrete, are discussed in Chapter 5.

Table 4.4 M i x proportions selected for further study*

M i x

Cem ent (kg/ m3)

Silica fume (kg/ m 3)

Poly mer (kg/ m 3)

Fine aggregate

(kg/m3)

Coarse aggregate

(kg/m3)

Water (kg/ m 3)

Super-plasticiz

er (% )**

A i r entaining agent**

Plain 453 43.8 0 795.5 1052.7 139 0.8-1.1 0.5-1.2 ml/kg

P M C -05

453 43.8 24.8 766.6 1015.4 139 0.5-0.8 0

P M C -10

453 43.8 49.7 737.7 978.1 139 0.3-0.5 0

P M C -15

453 43.8 74.5 709.6 940.8 139 0 0

* Water/'Cementitious materials (cement and silica fume) ratio is 0.28 *by weight of cementitious materials

35

4.3 Experimental program

The objective of the research was to study the fresh and hardened F R C with polymer

modification, in particular the compressive strength and flexural toughness of the

composites. Cylinders and beams were cast to determine these properties. The detailed

experimental program, with different amounts of fiber and latex, is shown in Table 4.5.

4.4 Test methods

4.4.1 Fresh concrete

In the present study, a pan-type concrete mixer was used. In order to avoid fiber

balling, a portion of the fibers was added before addition of the mixing water, and the

rest was added afterwards. Latex was added together with half of the water. The rest of

the water was used to rinse and keep all of the polymer in the mix. After mixing 3

minutues, tests of fresh concrete were conducted: slump test, air content, V B time (in part

of the program) and unit weight (i.e. density), carried out according to A S T M C143,

A S T M C231, and BS1881[55], respectively. Sampling of the fresh concrete was

performed in accordance with A S T M C172. After curing for the desired number of days,

concrete cylinders or beams specimens were ready for the hardened concrete tests.

4.4.2 Hardened concrete

4.4.2.1 Compressive strength

Compressive strength test were carried out according to A S T M C 39. A t least three

cylinder specimens (100x200 mm) for each group were tested. A l l of the tests were

carried in a 400,0001b (~l,779kN) capacity Baldwin universal testing machine in the

U B C C iv i l Engineering Structures Laboratory.

36

Table 4.5 Test program

Category Code Polymer Steel Fiber

HPP Fiber

PPN Fiber

Control (Mix#l) Plain . . . — — PMC

(Mix#2) P M C 15 15% — — — (Mix#3) P M C 1 0 ' .10% — — (Mix#4) P M C 0 5 5% — . . . . . .

FRC (Mix#5) SFRC0.5 0.5% (Mix#6) SFRC1.0 1.0% . . . —

(Mix#7) HPP-FRC0 .5 — — 0.5% — (Mix#8) H P P - F R C 1 . 0 — . . . 1.0%

(Mix#9) P P N - F R C 0 . 5 — — — 0.5% (Mix#10) P P N - F R C 1 . 0 — . . . — 1.0%

PM-FRC (M ix# l l ) PM5-SF0.5 5% 0.5% . . . — (Mix#12) PM5-SF1.0 5% 1.0% . . . . . .

(Mix#13) PM10-SF0.5 10% 0.5% — . . .

(Mix#14) PM10-SF1.0 10% 1.0% .__ __.

(Mix#15) PM15-SF0.5 15% 0.5% . . . . . .

(Mix#16) PM15-SF1.0 15% 1.0% . . . . . .

(Mix#17) PM15-SF2.0 15% 2.0% . „ . . .

(Mix#18) PM5-HPP0.5 5% — 0.5% . . .

(Mix#19) PM5-HPP1 .0 5% — 1.0% . . .

(Mix#20) PM10-HPP0.5 10% — 0.5% . . .

(Mix#21) PM10-HPP1.0 10% — 1.0% — (Mix#22) PM15-HPP0.5 15% — 0.5% — (Mix#23) PM15-HPP1.0 15% — 1.0% . . .

(Mix#24) PM5-PPN0.5 5% — 0.5% (Mix#25) PM5-PPN1.0 5% — 1.0% (Mix#26) PM10-PPN0.5 10% — . . . 0.5% (Mix#27) PM10-PPN1.0 10% . . . . . . 1.0% (Mix#28) PM15-PPN0.5 15% — — 0.5% (Mix#29) PM15-PPN1.0 15% — — 1.0%

Hybrid (Mix#30) P M O - S F / P P N 0 0.5 0.5 (Mix#31) P M 1 5 - S F / P P N 15% 0.5 0.5 (Mix#32) P M 1 5 - S F / P P N 15% 1.0 — 1.0

37

4.4.2.2 Water absorpt ion

The water absorption test was based on the procedures outlined in R I L E M P C M - 1 1 ,

except that the specimen was a 75x150 mm cylinder instead of a 4x4x16 mm prism

specimen [56]. In this test, the weighed specimens were completely immersed in a

container of water held at 18~22°C. After 48 hours the specimens were removed from the

water, and all surface water was wiped off with a damp cloth. They were then weighed

immediately, and the results recorded as the wet mass. In the present program, the

absorption process was also measured as a function of time in addition to the final value.

The water absorption of the specimens is calculated from the following equation.

W A = (W-D) /Dx l00 (4.1)

Where WA=water absorption (%), D=dry mass (g) after air-drying for two months,

W=Wet mass (g).

Concrete is a relatively impermeable method. Therefore, the penetration of water into

concrete is slow, and it is not really possible to obtain moisture equilibrium (i.e.,

complete saturation) of a 75 mm diameter cylinder in only 48 hours. Thus, the water

absorption reported here can only be used for relative comparison amongst the different

types of concrete.

4.4.2.3 Static modulus of elasticity (E)

The determination of the static E value was based mainly on a combination of

R I L E M P C M - 6 for polymer modified mortar, and the A S T M C469-94 method. The test

setup in the present study used a modified compressometer as per A S T M 469-94. Two

L V D T s were used to detect the longtitudtional deformation, as shown in F ig . 4.5 [57].

The chord modulus of elasticity of P M C was calculated as follows;

E=(S2-Sl)/(s-0.000050) (4.2)

38

Where, E = static elastic modulus, SI = compressive stress corresponding to a

compressive strain o f 0.000050 (MPa), S2 = compressive stress corresponding to 1/3 of

maximum load (MPa), s = compressive strain produced by the compressive stress S2.

Figure 4.5 Test Setup for Measuring Modulus of Elasticity of P M C

4.2.3.4 F lexura l Toughness

The flexural test is the most common test on hardened fiber reinforced concrete, in

part because it is easy to carry out compared with direct tension or shear tests. From a

flexural test, one can obtain information about matrix properties, fiber efficiency, and

energy absorption. In this study, the synergy between polymers and fibers, i f any, was

also evaluated from this test.

In this investigation, at least four 1 Ox 100x350mm beam specimens were cast to

determine the flexural toughness, generally in accordance with A S T M C1018. Flexural

toughness and first crack strengths were obtained, using different ways of analyzing the

load vs deflection curve.

Fig. 4.6 shows the flexural testing system employed. The load and deflection were

continuously recorded using three channels of the data acquisition system. In all methods

of analysis, the deflection used should be the true center point deflection of the beam,

related to the neutral axis o f the specimen. To make accurate deflection measurements, a

39

so-called "Japanese" yoke and two linear variable differential transformers (LVDTs)

were used, as shown in F ig . 4.7. For all tests, the rate of deflection was controlled at 0.10

mm per minute in an open loop I N S T R O N universal testing machine. The test was

carried out to a total deflection of about 2.8 mm.

Figure 4. 6 Setup of Flexural Test (with data acquisition system)

Figure 4.7 Arrangement of "Japanese" Yoke and L V D T s for Flexural Test

40

The analytical approaches of JSCE-SF-4 , post crack strength (PCS), and A S T M

C1018 were all used to characterize the properties of P M C , F R C and P M - F R C . The

specific details and significance of each method are described in Section 4.5.

4.5 F lexura l toughness analysis

The term "flexural toughness" is commonly used, but without any universally

accepted definition. Toughness may be described in quite different ways. Chen [58] has

given a good summary and critical comparison of most of the methods that have been

suggested. Overall,, three major categories can be classified: (1) absolute value defined in

terms of the area under the load vs. deflection curve; (2) relative value (also called

fracture index, defined in terms of the ratio of the areas out to different deflections under

the 1 oad v s. d eflection c urve), and ( 3) v alues w hich a re d efined i n t erms o f p articular

specimen dimensions and certain characteristics of the load vs. deflection curve.

As yet, there is no universally accepted definition of "flexural toughness", though

some are more commonly used than others due to their physical meaning and practical

importance. Three of these are described in detail below, and are subsequently used in

this study.

(1) A S T M C1018 [591

The concept is based on the load-deflection curve obtained in four point bending.

The deflection corresponding to the "first" crack is determined as the point at which the

curve first appears to become non-linear. Toughness indices IN (N=5, 10, 20, 30, etc.) are

then calculated by taking the ratio of the energy absorbed out to a certain multiple of first

crack deflection (i.e., the area under the load-deflection curve to that point) to the energy

consumed up to first crack deflection, as is schematically explained in Fig. 4.8. This may

be expressed by Eq.4.3:

Energy absorbed up to a certain multiple of first crack deflection I N = ( 4 3 )

Energy consumed up to first crack

41

Because F R C maintains some post-peak load carrying capacity, in this method a

"residual strength factor" is also defined, RM,N:

RM,N=C{I N - I M } (4.4)

Where C =100/(N-M). For an ideally brittle material, all of the indices are 1. The

residual strength factor for plain concrete is approximately equal to zero. B y this method,

one can describe both the first crack strength, and the post-crack behaviour of the

particular studied composite.

Area QABCl . ... Area OABEG Area OAJ 2 0 Area OAJ

05 38 5.58 10.58 Zero Midpo in t De f lec t i on L o a d

Figure 4.8. Schematic Description of the Flexural Toughness of A S T M C I 018 Method

However, there are some major concerns with this method. In particular, the

identification of the point of "first crack" is extremely difficult, and often appears to be

arbitrary. Consequently, the area used as the denominator in Eq.4.3 is susceptible to

large errors, leading to ambiguities in the calculated fracture index. A lso with this

method, the same index values can be calculated for totally different load-deflection

curves [60].

(2) J S C E - S F 4 method [61]

JSCE-SF4 provides another method for defining the flexural toughness of fiber

reinforced concrete. Unl ike A S T M C 1 0 1 8 , "first crack" identification is not necessary.

42

The area under the load -deflection curve up to a certain load point deflection of span

[Span(L)/150] is measured in this technique. A flexural toughness factor, FT , is

calculated as shown in Eq.4.5 and Fig. 4.9. It has units of stress, so that it can indicate

the average post-matrix cracking residual strength of the composite for deflections out to

L/150.

FT= A / - l 5 0 , / - \ " (4.5) (L/\50)BH2

where B, H and L are the breadth, height and span of the test beam, respectively. This

method has good precision and stability.

L / 1 5 0 D e f l e c t i o n

Figure 4.9. Schematic Description of Flexural Toughness Factor of JSCE-SF4 Method

However, J S C E SF-4 too has some problems. First, the deflection of L/150 chosen

for the end point is completely arbitrary, and has no significant or practical meaning from

the serviceability point of view [60]. In addition, because F T is measured using a

"smeared" approach (averaging the residual strength over the entire post-peak region),

these p arameters p rovide 1 ittle i nformation about t he m ain characteristics o f t he e ntire

load-deflection curve, such as first crack, instability and shape. Some of these

characteristics are, however, very important for F R C applications. Unfortunately all of

them are wrapped up in the total area under the curve [58].

In the present program, this technique is used to compare the total energy absorption

of different mixes.

43

(3) P C S methodr601

The Post Crack Strength approach (PCS) is a modification of the ASTMC-1018

method. The point of first crack need not be determined. Instead, the entire load vs.

deflection curve is divided into two parts: pre- peak load and post-peak load region. The

post crack strength values can be defined at various deflections as shown in Eq.4.6 and

F ig 4.10.

PCS m = ( E posl- =1 (4.6)

( — 5 peak ) BH 2

m

Deflection

Fig.4.10 Schematic Description of Flexural Toughness of the Post Crack Strength (PCS) Method

The value o f " m " can be chosen depending o n the application, and the suggested

factors L/m lie between L/3000 and L/150. Not surprising, when L/150 is used, the P C S

values are almost the same as the ones obtained from the J S C E - S F 4 method.

The great benefit of using this method is that by analyzing the shape of the curve,

fiber effects on the toughness at different stages of bending can be obtained.

44

CHAPTER 5 RESULTS

5.1 Optimizations of mix design for high strength P M C (trial tests)

Plain high strength concrete can now easily be produced by using superplasicizers

and mineral admixtures such as sil ica fume [62]. For high strength P M C , however, there

is no generally agreed upon technique, and so empirical tests must be carried out, due to

the fact that the polymer itself, or other related factors, may affect the strength

significantly. For the same cement type, these factors include the compatibility between

cement and polymer, polymer type and polymerization degree (which affect the f i lm-

forming temperature and the f i lm strength), applied dosage, air-entraining properties, etc.

In o rder t o o ptimize t he m ix p roportions f or a p articular c ompressive s trength a nd f or

other desired properties as wel l , several important properties of high strength P M C , such

as workabil ity, elastic modulus and water absorption, and the factors that affect them,

were investigated. These optimized mix proportions for high strength P M C were then

adopted for subsequent parts of the research program.

5.1.1 Workability

Good workability is essential for high strength concrete because less efficient

compaction may lead to loss of strength. Many factors, such as total water content, water

/cement ratio, supplementary cementitious materials, and aggregate shape and size, affect

workability. For ease of achieving the strength objective, the basic parameters such as

cement content, sil ica fume content, and water content were fixed for the reference plain

concrete. Only the following parameters were varied:

(1) Ratio of sand/total aggregate

For high strength concrete, the ratio of sand to total aggregate recommended by Cai

[63] ranges from 0.34 to 0.42 for crushed stone and 0.26 to 0.36 for gravel. There exists

an optimum sand content, which may not be sensitive for normal strength concrete. When

the same water/cement ratio is maintained, an increase of fine aggregate content may

reduce both workability and strength (unless more chemical admixture is applied),

45

because the specimen may not be easy to compact when still in its fresh state, A very

high mortar content may also lead to increases in shrinkage and creep properties.

In this research, ratios of 35%, 38%> and 43% were tried. The results showed that

concrete with 38%> sand had the best results when workability, strength and lower

admixture dosage were considered. However, a slightly higher sand content is helpful for

fiber dispersion. Suitable adjustments were made when fibers were incorporated (Section

5.2) in the final program.

(2) Antifoamer — A i r content

A i r content is another factor which must be considered. The right amount of air in

concrete is helpful for workability, and necessary for freeze-thaw resistance. As

mentioned earlier, polymers are l ikely to entrain excessive air in concrete, and so anti-

foamers are always applied to control air content. Table 5.1 lists the air content and the

slump and appearance of the concrete when different dosages of silicone emulsion were

used in P M C containing 15%> of S B R latex. In the end, an anti-foamer: latex ratio of

0.45%o, (for which the air content of the P M C 1 5 was 3.3%o) was used for all the

subsequent mixes containing polymers. I

Table 5.1 Effect of antifoamer on workability of P M C

Silicone emulsion /latex ratio

(%) P M C 15 Appearance

Slump (mm)

A i r content (%)

0 P M C 15 Flowable 195 5.5 0.45 P M C 15 Flowable 205 3.3 0.70 P M C 15 Flowable 200 3.2 1.50 P M C 15 Medium 155 2.6 2.00 P M C 15 Dry and harsh 120 1.8

(3) Polymer / cement ratio

Polymer content is the dominant factor influencing the workability of P M C . Table 5.2

shows the workability o f P M C in terms of both slump and V B time. The appearance of

P M C ' s with different polymer contents is shown in Figs.5.1-5.3. Obviously, the

workability was considerably improved by polymer addition, making the concrete

46

cohesive and easy to finish. When the polymer /cement ratio reached 15% or more, the

P M C developed almost a self-compacting character (Fig. 5.3(b)). If the consistency was

kept constant, in other words, less water was required. Thus latex played a role as a

superplasticizer in P M C due to its lubricating properties.

Table 5.2 Workability of polymer modified concrete (w/c =0.28)

Index Polymer cement ratio (%) 0 5 10 15

Slump (mm) • 0 , 10 55 195 VeBe time (s) 31 20 — —

Appearance Very dry Dry Medium Sticky Viscous and flowable

(4) Chemical admixtures

Chemical admixtures, such as superplasticizers (SP) and air entraining agents (AE)

are often used in concrete to get the desired workability as well as other benefits. Based

on previous research, additional air-entraining admixtures are not necessary in P M C . On

the contrary, antifoamers are often used to control the high air contents caused by the

surface-active properties of the latex. In this program, different amounts of

superplasticizers were tested to determine the optimum amount of superplasticizer.

To get similar consistency or slump (190mm to 200mm), different combinations of

polymer and superplasticizer are necessary for a given dosage of polymer when the

polymer /cement ratio (p/c) is less than 15%. Table 5.3 gives the test results, which

indicate that a combination of 0.5% SP and 0.8% A E is equivalent to 15% polymer. For

the case of lower p/c ratio, more superplasticizer should be applied. Similar trends were

observed when medium slump (80mm-100mm) concrete was made, but a smaller dosage

of superplascizer was used. Superplasticizers seem to be more effective when used with

higher latex dosages.

47

P M C o5 P M C -15 Figure 5.1 Appearance of P M C with 5%

Latex (a) P M C 15 after mixing

Figure 5.2 Appearance of P M C with 10% Latex

(b) P M C 15 after Slump Test Figure 5.3 Appearance of P M C with

15% Latex

48

Table 5.3 Effects of chemical admixture on workability of P M C *

Polymer** Slump Dosage of SP Dosage of A E A i r content /cement*** (mm) (%) (%) (%)

(%) 0 192 0.85 0.8 4.5 0 110 0.60 0.8 4.2 5 200 0.58 0 2.9 5 80 0.31 0 . . .

10 200 0.26 0 3.3 10 95 0.11 0 . . .

15 195 0 0 3.5 *Ratio of fine aggregate to total =0.38; * * silicone emulsion anti-foamer; ***total cementitious material

5.1.2 Compressive strength

(1) Polymer content and curing methods

Because polymer addition may form a f i lm on the surface of the cement particles,

special curing is necessary for normal strength concrete, as has been shown by various

researchers [1,10]. In this program, in order to optimize the curing method for high

strength P M C , three curing conditions were studied to observe the effects of curing

methods on compressive strength, so that a suitable curing condition could be chosen for

use in the subsequent study. These curing methods are described below:

Method #1 2 days in the mould covered with a plastic sheet, and then water

curing until the test date. Method #2 2 days in the mould covered by a plastic sheet,

five days of water curing, and then air curing to the test date. Method #3 — A i r curing

to the test date.

Results in terms of the 28-day compressive strength are shown in Table 5.4. Clearly,

method #2 is best for high polymer /cement ratios, while method #1 is best for concrete

with lower polymer contents (including plain concrete). The reasons for this wi l l be

discussed in Chapter 6. Thus method #2 method for P M C was chosen as the optimum

curing approach, while wet curing was used for plain high strength concrete.

49

Table 5.4 Compressive strength of P M C for different curing methods

Concrete M i x

28-day Compressive strength (MPa) Concrete

M i x Method #1

Wet Method #2

Wet-then-dry Method #3

Dry (air curing) P L A I N 87.21 — — P M C 0 5 96.71 85.66 83.09 P M C 10 76.59 81.64 74.84 P M C 15 66.41 76.42 67.3 1

(2) Time dependence of compressive strength of P M C

The compressive strength development of high strength P M C was also studied.

Results at different curing ages ti l l 28days are shown in Table 5.5. It may be concluded

that after 21 days, the compressive strength reached more than 95% of the 28-day

strength regardless of polymer/cement ratio.

Table 5.5 Time dependence of compressive strength of P M C *

Polymer content

(%)

Compressive strength (MPa) Polymer content

(%) 7d 14d 21d 28d

5 . 70.20 — . . . 85.91 5 — 94.31 — 97.13 5 — — 84.50 85.66 10 61.45 — . . . 72.46 10 — 72.28 . . . 80.93 10 — . . . 79.76 81.64 15 — . . . 71.54 72.75 15 — . . . 68.81 68.82 15 — 70.12 — 76.42

*Curing method #2: first 2 days covered, 5 days in the water, then air curing to test date.

5.1.3 Elastic modulus

Figs.5.4 - 5.7 show the uniaxial compressive responses of high strength P M C . The

elastic modul i under compressive 1 oading were calculated according to Eq .4 .2andare

compared in Table 5.6. The latex modified concretes showed a decrease in elastic

50

modulus with the addition of latex, especially for more than 10% latex. Clearly, the

deformation behaviour of P M C 10 and P M C 15 was different from that of ordinary

concrete.

Table 5.6 Elastic modulus of high strength concrete with polymer

Concrete Strain Loadl Stress Strain Load 2 Stress E Mix s i (kN) SI s (kN) S2 (GPa)

(millionths) (MPa) (millionths) (MPa) PMCO 0.00005 30.59 3.919 0.0730/100 237.53 30.44 42.09 P M C 0 5 0.00005 31.72 4.065 0.0715/100 241.30 30.92 43.66 P M C 10 0.00005 25.08 3.214 0.0845/100 227.55 29.16 35.11 P M C 15 0.00005 30.63 3.926 0.0892/100 234.78 30.08 33.02 * 100mm x 200mm cylinder specimen

5.1. 4 Water absorption of P M C

Results of the water absorption of high strength P M C are shown in Table 5.7. A

considerable d ecrease i n t his p arameter w ith i ncreasing 1 atex v olumes i mplies t hat t he

microstructure, in particular the porosity or pore structure, has been modified.

Table 5.7 Water absorption of polymer modified concrete

Concrete M i x

Polymer: cement

ratio (%)

Water absorption (%) Concrete

M i x

Polymer: cement

ratio (%)

0 hour 2.5hours 6 hours 26 hours 48 hours

Plain 0 0 0.702 0.865 1.229 1.370 PMC-05 5% 0 0.203 0.243 0.426 0.487 P M C - 1 0 10% 0 0.143 0.204 0.369 0.410 PMC-15 15% 0 0.105 0.105 0.295 0.358

75mmxl50mm cylinders specimen.

5.1.5 Summary of mix design for high strength P M C

Based on the above preliminary experiments, it was found that the desired

compressive strengths could be achieved with different polymer / cement ratios. The

compressive strengths ranged from about 65 M P a to 85 M P a , though compressive elastic

51

moduli were greatly reduced with increasing latex content. Other properties of high

strength concrete with styrene-Butadiene latex, such as workability and water-absorption

ability, were also improved significantly. The following parameters were chosen for the

high strength P M C system:

(1) Water/cementitious materials ratio =0.28;

(2) Fine aggregate/total aggregate 38-43%;

(3) Polymer/cement ratio 0—15%;

(4) Antifoam/polymer 0.45~0.70%(solid/solid).

52

800

700

600

Z 500

400 n ° 300

200

100

0

/ PM0-1#

PM0-2#

PM0-3# A PM0-1#

PM0-2#

PM0-3#

PM0-1#

PM0-2#

PM0-3#

,. .,

0.1 0.4 0.2 0.3 Deflection (mm)

Figure 5.4 Load-deflection curve of cylinder under compression(Plain/PMC0)

0.5

PM05-1#

PM05-2#

PM05-3#

PM05-1#

PM05-2#

PM05-3# - J Z i .

PM05-1#

PM05-2#

PM05-3#

/ • 1 1 1 ,

0.1 0.4 0.2 0.3 Deflection (mm)

Figure 5.5 Load-deflection curve of concrete in compression (PMC05)

0.5

53

800

700 -

600

z 500 -

T3 400 -ro O 300 -

_ l 300 -

200

100

PM10-1#

PM10-2#

PM10-3# /?*

PM10-1#

PM10-2#

PM10-3# / Jr

-/

PM10-1#

PM10-2#

PM10-3#

T^-f

/ 0.1 0.4 0.2 0.3

Deflection (mm) Figure 5.6 Load-deflection curve of concrete in

compression(PMC10)

0.5

54

5.2 Results for composites with polymer and/or fibers

5.2.1 Workability of fresh concrete

As mentioned earlier, the workability of fiber reinforced concrete, which is important

for practical applications, has different characteristics from that of conventional concrete

[64]. Thus the optimized P M C and plain mixes from the previous section could not be

used directly. In order to achieve good workability for this part of the investigation, some

adjustments were made to these F R C and P M - F R C composites. First, the sand content

(sand/total aggregate) was adjusted from 38% to 43%, which effectively improved fiber

dispersion in the fresh concrete; different amounts of superplasticizer were added to

compensate for the workability loss due to fiber addition and the increase in fine

aggregate. Workabi l i ty data for a l l the 3 2 mixes are shown i n Table.5 .8. The results

indicated that most mixes had slumps ranging from 60-90 mm when lower dosages of

polymer were added. For higher polymer additions, say 15%, even without using a

superplasticizer, the slump values were much higher, ranging from 150mm to 200 mm

due to the water-reducing property of the polymer. Even for mix #17 and #32, where a

much higher total volume fraction (Vf=2.0%>) of fiber was used, the polymer was able to

provide an acceptable workability.

Because fiber additions make the slump test an insensitive measure f or evaluating

workability, the V e B e test is often used as a more effective alternative. In this program

both the VeBe test and the slump test were carried out for mixes containing fibers. The

VeBe times are also shown in Table 5.8, ranging from 0 to 6 seconds. This indicates that

these mixes were easy to compact, particularly those mixes with 10% or more polymer

and H P P fibers, after some adjustments were made.

The effects of different fibers on workability can also be evaluated by comparing the

admixture dosage and /or workability data for similar mixes, such as mixes #5, #7 and #9,

or mixes #6, #8 and #9. Adjusted admixture dosages are recorded in Table 5.9. These

results show that for the same volume fraction of fibers, the effect o f the fibers on

workability is in the order: P P N fiber>steel fiber> H P P fiber. The P P N fiber has the

greatest effect on workability due to its larger surface area and its special texture.

55

Table 5.8 Results of workability tests

Category Description Poly mer

Steel Fibe

r

HPP Fibe

r

P P N Fiber

Workability Category Description Poly mer

Steel Fibe

r

HPP Fibe

r

P P N Fiber Slump

(mm) VeBe time

(s) Control (Mix#l)

Plain — — — — 75 —

P M C (Mix#2) P M C 5 5% . . . — . . . 80 _._

(Mix#3) P M C 10 10% — . . . — 95 . . .

(Mix#4) P M C 15 15% _ _ _ — . . . 200 „ .

F R C (Mix#5) SFRC0.5 — 0.5% — — 65 2 (Mix#6) SFRC1.0 1.0% — — 60 3 (Mix#7) HPP-FRC0 .5 — — 0.5% — 70 1 (Mix#8) H P P - F R C 1 . 0 — — 1.0% — 70 2.5 (Mix#9) P P N - F R C 0 . 5 — — — 0.5% 70 3.5

(Mix#10) P P N - F R C 1 . 0 .__ . . . . . . 1.0% 80 5.5 P M - F R C (M ix# l l ) PM5-SF0.5 5% 0.5% — . . . 60 3 (Mix#12) PM5-SF1.0 5% 1.0% — — 52 4 (Mix#13) PM10-SF0.5 10% 0.5% . . . — 70 1 (Mix#14) PM10-SF1.0 10% 1.0% . . . — 50 3 (Mix#15) PM15-SF0.5 15% 0.5% — . . . 165 0 (Mix#16) PM15-SF1.0 15% 1.0% — — 145 0 (Mix#17) PM15-SF2.0 15% 2.0% . . . . . . 75 3

(Mix#18) PM5-HPP0.5 5% — 0.5% . . . 110 0 (Mix#19) PM5-HPP1 .0 5% . . . 1.0% — 70 2 (Mix#20) PM10-HPP0.5 10% — 0.5% — 115 0 (Mix#21) PM10-HPP1.0 10% — 1.0% — 70 2 (Mix#22) PM15-HPP0.5 15% — 0.5% — 180 0 (Mix#23) PM15-HPP1.0 15% — 1.0% . . . 150 0

(Mix#24) PM5-PPN0.5 5% — — 0.5% 60 2 (Mix#25) PM5-PPN1.0 5% — — 1.0% 85 3 (Mix#26) PM10-PPN0.5 10% — 0.5% 80 1.5 (Mix#27) PM10-PPN1.0 10% — — 1.0% 100 3 (Mix#28) PM15-PPN0.5 15% — 0.5% 160 0 (Mix#29) PM15-PPN1.0 15% — . . . 1.0% 168 0 Hybrid

(Mix#30) P M O - S F / P P N 0 0.5% 0.5% 110 3 (Mix#31) P M 1 5 - S F / P P N 15% 0.5% 0.5% 155 0 (Mix#32) P M 1 5 - S F / P P N 15% 1.0% 1.0% 70 4

56

Table 5.9 Admixture dosages


Steel Fiber

HPP Fiber

P P N Fiber

Admixture dosage Category Description Poly mer

Steel Fiber

HPP Fiber

P P N Fiber A E *

(%) SP* (%)

Control (Mix#l)

Plain — — — — 0.08 0.6

P M C (Mix#2) P M C 5 5% — . . . . . . 0 0.68 (Mix#3) P M C 10 10% — — . . . 0 0.18 (Mix#4) P M C 15 15% — . . . — 0 0

F R C (Mix#5) SFRC0.5 . . . 0.5% . . . — 0.08 0.61 (Mix#6) SFRC1.0 — 1.0% — — 0.08 0.70 (Mix#7) HPP-FRC0 .5 — — 0.5% — 0.08 0.52 (Mix#8) H P P - F R C 1 . 0 — — 1.0% . . . 0.08 0.56 (Mix#9) P P N - F R C 0 . 5 — — — 0.5% 0.08 0.64

(Mix#10) P P N - F R C 1 . 0 — — — 1.0% 0.08 0.73 P M - F R C (M ix# l l ) PM5-SF0.5 5% 0.5% . . . . . . 0 0.21 (Mix#12) PM5-SF1.0 5% 1.0% . . . — 0 0.42 (Mix#13) PM10-SF0.5 10% 0.5% — . . . 0 0.145 (Mix#14) PM10-SF1.0 10% 1.0% — . . . 0 0.28 (Mix#15) PM15-SF0.5 15% 0.5% — . . . 0 0 (Mix#16) PM15^SF1.0 15% 1.0% . . . . . . 0 0.17 (Mix#17) PM15-SF2.0 15% 2.0% . . . . . . 0 0.28

(Mix#18) PM5-HPP0.5 5% — 0.5% _ — • 0 0.20 (Mix#19) PM5-HPP1 .0 5% — 1.0% . . . 0 0.35 (Mix#20) PM10-HPP0.5 10% . . . 0.5% . . . 0 0.07 (Mix#21) PM10-HPP1.0 10% — 1.0% — 0 0.105 (Mix#22) PM15-HPP0.5 15% . . . 0.5% . . . 0 0 (Mix#23) PM15-HPP1.0 15% — 1.0% . . . 0 0

(Mix#24) PM5-PPN0.5 5% — — 0.5% 0 0.23 (Mix#25) PM5-PPN1 .0 5% . . . — 1.0% 0 0.48 (Mix#26) PM10-PPN0.5 10% — . . . 0.5% 0 0.17 (Mix#27) PM10-PPN1.0 10% — . . . 1.0% 0 0.30 (Mix#28) PM15-PPN0.5 15% — — 0.5% 0 0.07 (Mix#29) PM15-PPN1.0 15% — . . . 1.0% 0 0.14 Hybrid

(Mix#30) P M O - S F / P P N 0 0.5% 0.5% 0.08 0.61 (Mix#31) P M 1 5 - S F / P P N 15% 0.5% 0.5% 0 0.14 (Mix#32) P M 1 5 - S F / P P N 15% 1.0% 1.0% 0 0.35 *SP—Superplasticizer and A ' ',— air entaining agent, by weight of cementitious material

57

5.2.2 Density of concrete

The density of concrete both in the fresh state and after 28 day curing was

determined, as shown in Table 5.10 (Due to unavoidable equipment problems, some fresh

densities could not be measured.) Consistent results were observed, with only slight

changes for different fiber volumes and polymer contents. The minimum density in the

hardened state (2327 kg /m 3 ) was obtained for mix #10 with 1% of P P N fiber; and the

maximum density (2654 kg/m 3) was obtained for mix #12 with 5% polymer and 1% steel

fiber. A n increase of density was observed with an increase of steel fiber volume (see

mixes #15, #16 and #17). A lso, a higher polymer content seemed to reduce the density

(see mixes # 2, #3 and #4).

5.2.3 Compressive strength

Because an optimized curing procedure is essential for the production of high

strength P M C , all of the high strength concretes containing polymers in this program

were cured under the wet-dry condition described in Section 5.1.2. For those mixes

without polymer additions, the cylinders were subjected to normal water-curing method

for 28 days. Compressive strengths are shown in Table 5.11. The maximum compressive

strength was obtained for M i x #12 (PM5-SF1.0), 94.31 M P a , while the minimum

strength was for mix # 28 (PM15-PPN0.5), 62.53 M P a . The compressive strength trend

depends on the polymer content rather than the fiber content, since no more than 1.0% of

fiber was used. Although some increases may be observed for the mixes with steel fibers

(by comparing mixes #5 and #6, mixes #11 and #12, mixes #13 and #14), some decreases

may be observed for those mixes with polymeric fibers (by comparing mixes #7 and 8,

mixes #9 and #10, mixes #18 and #19, and mixes #22 and #23).

58

Table 5.10 Density of fresh and hardened concretes

Concrete code

Description Poly mer

Steel Fiber

HPP Fiber

P P N Fiber

Density (kg/m3) Concrete code

Description Poly mer

Steel Fiber

HPP Fiber

P P N Fiber In fresh

state Hardened

state Control (Mix#l)

Plain P M C O

— — — — 2387 —

P M C (Mix#2) P M C 5 5% . . . . . . . . . — 2545 (Mix#3) P M C 10 10% — — . . . . . . 2519 (Mix#4) P M C 15 15% — . . . — — 2480

F R C (Mix#5) SFRC0.5 0 0.5% . . . . . . _ _ _

(Mix#6) S F R C 1.0 0 1.0% — . . . 2442 —

(Mix#7) H P P - F R C 0 . 5 0 — 0.5% — — 2422 (Mix#8) H P P - F R C 1 . 0 0 — 1.0% — 2353 2401 (Mix#9) P P N - F R C 0 . 5 0 . . . . . . 0.5% . . . 2397

(Mix#10) PPN-FRC1.0 0 . . . — 1.0% 2327 2373 P M - F R C (M ix# l l ) PM5-SF0.5 5% 0.5% — — — 2562 (Mix#12) PM5-SF1.0 5% 1.0% . . .

— 2566 2654 (Mix#13) PM10-SF0.5 10% 0.5% . . . 2500 2521 (Mix#14) PM10-SF1.0 10% 1.0% — — 2555 2594 (Mix#15) PM15-SF0.5 15% 0.5% — 2459 2471 (Mix#16) PM15-SF1.0 15% 1.0% — 2488 2501 (Mix#17) PM15-SF2.0 15% 2.0% — — 2578 2634

(Mix#18) PM5-HPP0.5 5% — 0.5% — . . . 2544 (Mix#19 PM5-HPP1.0 5% — 1.0% . . . 2497 2547 (Mix#20) PM10-HPP0.5 10% — 0.5% — . . . 2493 (Mix#21) PM10-HPP1.0 10% — 1.0% — . . . 2533 (Mix#22) PM15-HPP0.5 15% — 0.5% — — 2473 (Mix#23) PM15-HPP1.0 15% . . . 1.0% . . . 2416 2479

(Mix#24) PM5-PPN0.5 5% — . . . 0.5% 2494 2538 (Mix#25) PM5-PPN1 .0 5% — . . . 1.0% 2514 2521 (Mix#26) PM10-PPN0.5 10% . . . — 0.5% . . . 2502 (Mix#27) PM10-PPN1.0 10% — 1.0% 2462 2470 (Mix#28) PM15-PPN0.5 15% — . . . 0.5% 2419 2474 (Mix#29) PM15-PPN1.0 15% — — 1.0% . . . 2485 Hybrid

(Mix#30) P M O - S F / P P N 0 0.5 0.5 — 2419 (Mix#31) P M 1 5 - S F / P P N 15% 0.5 0.5 — 2528 (Mix#32) P M 1 5 - S F / P P N 15% 1.0 — 1.0 2476 2563

59

Table 5.11 Compressive strengths


Steel Fiber

HPP Fiber

P P N Fiber

Av Compressive strength (MPa)

Control (Mix#l)

Plain ( P M C O )

— — — — 89.03

P M C (Mix#2) P M C 5 5% — — 85.66 (Mix#3) P M C 10 10% — — — 81.64 (Mix#4) P M C 15 15% — . . . . . . 76.42

F R C (Mix#5) SFRC0.5 0 0.5% — — 85.03 (Mix#6) SFRC1.0 0 1.0% — — 88.04 (Mix#7) HPP-FRC0 .5 . . . . . . 0.5% . . . 75.10 (Mix#8) H P P - F R C 1 . 0 — — 1.0% — 71.08 (Mix#9) P P N - F R C 0 . 5 — — — 0.5% 71.25

(Mix#10) P P N - F R C 1 . 0 — — — 1.0% 69.64 P M - F R C (M i x# l l PM5-SF0.5 5% 0.5% — 87.24 (Mix#12) PM5-SF1.0 5% 1.0% — — 94.31 (Mix#13 PM10-SF0.5 10% 0.5% — . . . 74.76 (Mix#14) PM10-SF1.0 10% 1.0% . . . — 80.93 (Mix#15) PM15-SF0.5 15% 0.5% — . . . 69.89 (Mix#16) PM15-SF1.0 15% 1.0% — — 66.14 (Mix#17) PM15-SF2.0 15% 2.0% . . . — 71.51

(Mix#18) PM5-HPP0.5 5% . . . 0.5% — 89.05 (Mix#19) PM5-HPP1 .0 5% — 1.0% . . . 80.39 (Mix#20) PM10-HPP0.5 10% — 0.5% — 79.47 (Mix#21) PM10-HPP1.0 10% — 1.0% . . . 66.87 (Mix#22) PM15-HPP0.5 15% — 0.5% — 66.17 (Mix#23) PM15-HPP1.0 15% — 1.0% . . . 62.79

(Mix#24) PM5-PPN0.5 5% — — 0.5% 85.83 (Mix#25) PM5-PPN1.0 5% — . . . 1.0% 85.91 (Mix#26) PM10-PPN0.5 10% — — 0.5% 72.92 (Mix#27) PM10-PPN1.0 10% — — 1.0% 68.53 (Mix#28) PM15-PPN0.5 15% — 0.5% 62.53 (Mix#29) PM15-PPN1.0 15% — — 1.0% 63.31 Hybrid

(Mix#30) P M O - S F / P P N — 0.5 . . . 0.5 70.77 (Mix#31) P M 1 5 - S F / P P N 15% 0.5 — 0.5 68.17 (Mix#32) P M 1 5 - S F / P P N 15% 1.0 — 1.0 68.81

60

5.2.4 F lexura l behaviour of P M C , F R C and P M - F R C

Though some of the mixes with steel fibers showed an improvement in compressive

strength due to the inclusion of fibers, the P M C mixes tended to show a decrease in

compressive strength when higher dosages of latex were used. However, the compressive

strength of these materials is only of limited practical interest, except as one of the

quality control measures. The main benefits of fibers and polymers in cement-based

composite are not enhanced strength, but rather increased toughness and durability. These

are often determined using a flexural test.

(1) Stress vs. strain response

The load vs. deflection responses of the 32 different mixes were obtained using the

data acquisition system of an Instron testing machine, which was operated under open

loop conditions. Because of the brittle behaviour of concrete, some mixes failed in a

sudden manner, much faster than the data-acquisition rate. During this short period a

large amount of energy stored in the specimen and the test machine was released.

Accordingly, the measured load vs. deflection curves showed an instability just after peak

load. This occurred particularly when the load was high and the fiber volume fraction was

low. In order to correct for the energy stored in the specimen and machine, these curves

were modified by "mov ing" the deflection at break point (82, at point B) to the peak load

deflection (81, at point A ) , as schematically shown in Fig. 5.8. The flexural toughness for

all mixes, i f this kind of unstable manner was shown, was calculated based on the

modified curves.

Figs.5.9 to 5.40 show the individual load vs. deflection relationships for all of the

mixes in this study; in each figure, the dark line represents the average value.

61

L o a d *

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Unstable part, line C B , due to open-loop setup

81 82 Deflection

Fig.5.8 The Modification of Load-Deflection Curve in Flexural Toughness calculating

(2) First crack strength and toughness analysis

A s mentioned in Chapter 4, all of the load vs. deflection curves obtained were

analyzed to determine the toughness characteristics of these composites. Toughness

indices and residual strength factors according to A S T M C-1018, and the flexural

toughness factor according to J S C E SF-4 are shown in Table 5.12.

In order to provide a more rational means of characterizing the toughness, both at

small and large deflections, a modified method based on both A S T M and J S C E methods,

the P C S technique [60] was used to analyze all of the flexural load-deflection plots. The

results of the modulus of rupture (MOR) and post-crack strength values are reported in

Table 5.13. In this method, the P C S of each mix is shown for nine different deflection

values, i.e. L/m ratio ranges from 0.1 (PCS3000) to 2.0 (PCS 150).

62

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30

10

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0

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Figure 5.10 Load-deflection response of beams with 5% latex (mix#2 PMC5)

69

0.5 1.5 D e f l e c t i o n ( m m )

Figure 5.11 Load-deflection response of beams with 10% latex (mix#3 PMC10)

— 1 #

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70

30


Figure 5.13 Load-deflection response of beams with 0.5% of steel fiber (mix #5 SFRC0.5)

71

72

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2 5


Figure 5.18 Load-deflection response of beams with 1.0% PPN fiber (Mix#10 PPNFRC1.0)

73

7 4

75

0.5 1 1.5 D e f l e c t i o n ( m m )

Figure 5.23 Load-deflection response of beams with 15% of latex and 0.5% of steel fiber (Mix#15 PM15-SF0.5)

0 0.5 1 1.5 D e f l e c t i o n ( m m )

Figure 5.24 Load-deflection response of beams with 15% of latex and 1.0% of steel fiber (Mix#16 PM15-SF1.0)

76

0 0.5 1 1.5 2 D e f l e c t i o n ( m m )

Figure 5.25 Load-deflection response of beams with 15% of latex and 2.0% of steel fiber (Mix #17 PM15-SF2.0)

0.5 1 1.5 d e f l e c t i o n ( m m )

Figure 5.26 Load-deflection response of beams with 5% of Latex and 0.5% of HPP fiber (Mix #18 PM05-HPP0.5)

77

0.5 1 1.5 Deflection (mm)

Figure 5.28 Load-deflection response of beams with 10% of latex and 0.5% of HPP fiber (Mix #20 PM10-HPP0.5)

78

0 , — , j 0 0.5 1 1.5 2


Figure 5.29 Load-deflection response of beams with 10% of latex and 1.0% of HPP fiber (Mix # 21 P M 1 0 - H P P 1 . 0 )

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79

0.5 1 1.5 D e f l e c t i o n ( m m )

Figure 5.31 Load-deflection response of beams with 15% of latex and 1.0% of HPP fiber (Mix # 23 PM15-HPP1.0)

80

30

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Figure 5.33 Load-deflection response of beams with 5% of latex and 1.0% of PPN fiber (Mix #25 PM05-PPN1.0)

81

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0.5 1 1 5 Deflection (mm)

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0.5SF+0.5PPN)

83

0 I 1 1 1 0 0.5 1 1.5 2

Deflection (mm)

Figure 5.39 Load-deflection response of beams with 15% latex and hybrid 0.5% SF &PPN fiber (Mix #31 PM15--

SF0.5+PPN0.5)

50 T


Figure 5.40 Load-deflection response of beams with 15% of latex and hybrid 1.0% SF and PPN fiber (Mix #32 PM15-

SF1.0+PPN1.0)

84

CHAPTER 6 DISCUSSION

In this chapter, an analysis of the properties of the various composites is presented,

focusing on the influence of fibers and polymers on both the fresh and hardened concrete.

Compressive strength, flexural strength and especially flexural toughness are discussed,

based on the results given in Chapter 5.

6.1 Fresh concrete

6.1.1 Workab i l i t y of P M C

As m entioned i n S ection 5 .1.1, t he w orkability o f h igh s trength P M C i s d ifferent

from that of conventional concrete in terms of appearance, viscosity, and slump. The

water-reducing effects of S B R latex are very important as it improves concrete

workability considerably. Fig.6.1 shows the effects of polymer dosage on the slump and

VeBe time of fresh concrete ( P M C ) when the water/cement ratio was held constant. The

results indicate that the polymer played the same role as a superplasticizer, markedly

increasing the slump and decreasing the VeBe time for fresh concrete.

Alternatively, the admixture requirement to achieve similar consistencies can also be

used out to characterize the effects of the polymer. The results show that much smaller

dosages of superplasticizer (SP) and no air-entraining agent (AE) for P M C were needed

to achieve the target slump values when more polymer was added (Table 5.3 and

Fig.6.2). A s an approximation, the superplasticizing effect o f 15% o f latex is equivalent

to 0.85% SP and 0.08% A E for a target slump of 200mm, while 10% of latex is

equivalent to 0.5% SP and 0.08% A E for a target slump of 100mm. The equivalent

dosage of superplasticizer decreased by about 0.050% for every 1% of additional latex,

though it would appear that latex is slightly more effective as a superplasticizer for P M C

at higher target slump values (Fig.6.2).

85

250

0 2 4 6 8 10 12 14 16 P o l y m e r d o s a g e (%)

Figure 6.1 Effects of polymer dosage on workability of PMC

0.9

P o l y m e r d o s a g e (% w t )

Figure 6.2 Effect of superplacizer on workability of PMC for different polymer dosages

86

6.1.2 Workab i l i t y of F R C and P M - F R C

The workability of F R C mixes is summarized in Fig.6.3 (see also Table 5.8), in

which VeBe times and admixture dosages are shown for comparison. The results

indicate that both fiber type and. admixture dosage have significant influences on the high

strength F R C mixes studied here. The effects of different fibers on workability can be

evaluated by comparing the admixture dosage and /or workability data for similar mixes,

such as mixes #5, #7 and #9.(FRC0.5%), or mixes #6, #8 and #9 (FRC1.0%). Clearly, for

the same fiber volume fraction, F R C with HPP fibers has the lowest VeBe time, and is

thus the most workable mix, even though the admixture dosage (SP) was lower than that

of the other mixes; F R C with P P N fibers gave the highest VeBe time values. The effects

of the fibers on workability are in the following order:

P P N fiber > steel fiber > H P P fiber.

The P P N fiber has the greatest effect on workability due to its larger surface area and its

special texture after mixing.

When polymers were added to the F R C s , as expected, less superplasticizer was

required, and better characteristics resulted, such as less mixing friction, greater ease of

casting and better fmishability. Fig.6.4 shows the relationship between superplasticizer

and polymer dosages in P M - F R C s for a particular target slump (50mm ~ 80mm). As

mixes containing 15% polymer (PM15-FRCs) had slumps far beyond the target slump,

the polymer dosages listed in Fig.6.4 range only from 0 to 10%.

Even more effective effect of polymer on P M - F R C workability was observed when

15% polymer was added (Fig.6.5). Clearly, VeBe times for all mixes were reduced to

zero (Fig.6.5b), while the slump increased by 70 to 90 mm (Fig.6.5a). This may be

because the polymers not only increased the workability but also led to better fiber

distribution and decreased of balling of the fibers.

87

• A i r e n t a i n i n g a g e n t

s u p e r p l a s t i c i z e r

• V e B e t i m e



• V e B e t i m e



• V e B e t i m e

SFRC0.5 SFRC1.0 HPP-FRC0.5

HPP-FRCl.O

PPN-FRC0.5

PPN-FRC1.0

Figure 6.3 Workability of FRC

PMO PM5 PM10

Figure 6.4 Effects of polymer on dosage of superplacizer (PM-FRC mixes with target slump 50~80mm)

88

Slump (mm)

200 • "i PMO • PM5 UPM10 • PM15

SF0.5 SF1.0 HPP0.5 HPP1.0 PPN0.5 PPN1.0

Figure 6.5(a) Slump results of PM-FRC mixes

Vebe time (s)

PMO • PM5 • PM10 • PM15

SF0.5 SF1.0 HPP0.5 HPP1.0 PPN0.5

Figure 6.5(b) VeBe time for PM-FRC mixes

PPN1.0

89

6.2 Hardened concrete

6.2.1 Effects of cur ing method on compressive strength of P M - H S C

Test results on the effect of different curing methods on compressive strength have

been given in Section 5.1.2. The relationship between the strength o f polymer modified

high strength concrete ( P M - H S C ) and the curing method is re-plotted in F ig . 6.6. The

reasons for selecting the optimum curing procedure, with the objective o f high strength in

mind, are discussed in this section.

120

~ 100 ra

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40

20

• method #1-Wet

• method #2-Wet-then-dry

• method #3-dry

P M C 0 5 PMC10 Concrete type (latex content %)

P M C 1 5

Figure 6.6 Effects of curing method on compressive strength of P M C

From these results, it would appear that curing method #2 (wet, then dry) is better

than either continuous wet or dry curing (though the differences are not so large). This

can b e e xplained b y t he " self-desiccation" p roblem u nder c ontinuously dry c onditions

and the difficulty for polymer f i lm formation under wet conditions. For high strength

concrete with a very low w/c ratio, this problem is critical in the first few days after

casting, when the polymer f i lm is still not effectively formed and the moisture inside the

specimen is not easily maintained by the polymer f i lm, therefore negatively affecting the

90

cement hydration due to insufficient water. As would be expected, this is made even

worse i f t he e ntire curing p rocedure i s d ry. O n t he o ther h and, w hile c ontinuous w et

curing is good for conventional concrete with little or no polymer, it is harmful for the

fi lm formation of latex, especially when "f i lm-swel l ing" phenomena may occur for some

polymer after the formation of the f i lm.

It has been observed that, at a high dosage of polymer, a decrease of mechanical

strength occurs. This trend is clear when the polymer content reaches 15%. It may also be

noted that for high strength concrete c ontaining t he S B R latex used here, compressive

strength at the age of 14 days was equal to or greater than 90% of the 28 day strength,

which suggests that cement hydration has been accelerated compared to conventional

high strength concrete, but without any fast-setting problems. This property may be

helpful in repair projects such as bridge decks, which need to be re-opened to traffic as

quickly as possible.

6.2.2 Compressive strength of latex modified composites

Although compressive strength may be less important than properties such as

adhesion for polymer modified concrete, or toughness for fiber reinforced concrete, it is

still an important parameter for quality control and mix characterization. The

compressive strengths for the mixes in this study are summarized in Table 6.1 and Figs.

6.7 to 6.9, in which the results are organized based on the polymer content (from 5% to

15%), compared to plain high strength concrete without latex.

91

Table 6.1 Concrete compressive strength (MPa)

Fiber type and volume fraction

(%)

Polymer cement ratio (wt%)

Fiber type and volume fraction

(%) 0 5 10 15

Fiber v f Plain HSC PMC05 PMC 10 PMC15 No 0 89.0 85.7 81.6 76.4

Steel Fiber

v f SFRC PM05-SFRC PM10-SFRC PM15-SFRC Steel Fiber

0.5 85.0 87.2 74.8 69.9 Steel Fiber 1.0 88.0 94.3 80.9 66.1

Steel Fiber

2.0 — — — 71.5

P P N fiber

v f PPNFRC PM05-

PPNFRC PM10-

PPNFRC PM15-

PPNFRC P P N fiber 0.5 71.3 85.8 72.9 62.5 P P N fiber

1.0 69.6 85.9 68.5 63.3

H P P fiber

v f HPPFRC PM05-

HPPFRC PM10-

HPPFRC PM15-

HPPFRC H P P fiber 0.5 75.1 89.1 79.5 66.2 H P P fiber

1.0 71.1 80.4 66.9 62.8

Hybrid SF and P P N

v f PPN-SFRC PM5-

PPN-SFRC PM10-

PPN-SFRC PM15-

PPN-SFRC Hybrid

SF and P P N

0.5+0.5 70.8 — — 68.2

Hybrid SF and P P N 1.0+1.0 — — — 68.8

.0

P M O P M 0 5 P M 1 0 P M 1 5

Polymer cemetn ratio (%)

Figure 6.7 Compressive strength of concrete with steel fiber and latex

92

Compressive

HPP1.0 0.5

P M O P M 0 5 P M 1 0 P M 1 5

Polymer /cement ratio (%)

Figure 6.8 Compressive strength of concrete with latex and HPP fiber

Compressive strength (MBaf

PPN1.0 PPN0.5

HPPO

PMO PM05 PM10 PM15

Polymer cement ratio (%)

Figure 6.9 Compressive strength of concrete with latex and PPN fiber

9 3

These results indicate that at the same water/cement ratio the compressive strength

decreases w i th 1 atex additions. A t polymer: cement ratios greater than 1 0%, this trend

becomes particularly clear. This is due to the fact that the latex film itself has a low

compressive strength, as wel l as a low stiffness relative to the cement paste and aggregate

[65]. When the polymer: cement ratio is 15% or more, this dosage is sufficient for the

polymer to form a continuous phase with lower elastic modulus. When the concrete is

under load, the differences of the deformation of this extra "soft" phase (cement paste

with polymer) and other component could lead to high stress concentrations, though the

bonding may be improved in the interface. Consequently a significant decrease in the

compressive strength w i l l occur, even when enough antifoam agent is used.

When steel fibers were incorporated, the compressive strength increased somewhat,

but there was no significant effect on the concrete when polymeric fibers were used. For

the latex modified fiber reinforced concrete, the compressive strength ranged from 65

M P a to 94 M P a , which fit the design objective of this program.

M i x # 12 PM5-SF1.0 showed the highest compressive strength value, 94.3 M P a ;

M i x #28 showed the lowest value, 62.5 M P a . Over all, the polymer content played the

most important role in determining compressive strength.

6.2.3 Damage pattern of concrete cylinders under compression

The various concrete cylinders prepared for this study displayed different crack

modes and failure patterns. P M C s broke in a sudden and brittle manner, similar to plain

concrete, due to the high strength. The typical concrete "failure cone" can be observed,

and some cylinders spalled into many pieces. Fig.6.10 shows some typical broken

specimens of polymer modified concrete.

For the fiber reinforced concretes, the crack and damage patterns changed

considerably. After the peak load, the specimens still retained some residual strength,

since cracks were bridged by the fibers. Typical failure patterns o f the F R C s are shown in

Fig.6.11.

When latex and fibers were incorporated into the concrete, the P P N fiber specimens

showed a softer and more ductile mode of failure with an increase of polymer dosage. No

significant change of failure pattern could be observed for P M - H P P F R C , which was very

94

6.10(a) Typical failure cone 6.10 (b) PMC specimens Figure 6.10 P M C cylinders after compression

--v.™. . ™ ™ ™ ™ ™ ™ ™ ^ ^ ™ * - , . • . ,. ^ ^ ,

6.11(c) PPN-FRC0.5 6.12(c) PM10-PPN0.5 Figure 6.11 F R C cylinders after failure Figure 6.12 P M - F R C cylinders after

failure

95

similar to that without polymer. However, by comparing the effects of different

reinforcement types on the failure patterns of P M - F R C (Fig.6.11 and 6.12), it was found

that the cylinders with steel fibers and P P N fibers exhibited more ductility and greater

integrity after testing.

6.2.4 Elastic modulus and Water absorption ability

As noted in Chapter 5, the properties of the matrix are very important for all

composites, especially with regard to the deformability and the interfacial properties.

These properties must therefore be considered when explaining the performance of P M C

itself and of P M - F R C in which the P M C acts as the matrix.

The deformability of the matrix can be characterized by the elastic modulus, and

changes in pore structure can be obtained using various direct or indirect tests such as the

water absorption test used here [56]. The elastic modulus data are re-plotted in Fig. 6.13,

which shows that the elastic modulus in compression decreases with increasing polymer

dosage, although it may not be significantly a ffected by low dosages of polymer; at a

dosage of 5%, for instance, a small (3.7%) increase occurred. The decrease of E was

found to be 16.6% and 21.5% for P M C 1 0 and P M C 1 5 , respectively, when compared to

plain high strength concrete (HSC) (Table 6.2). In normal strength P M C (fc'=30 MPa) ,

the elastic modulus loss is only around 10% [12], which implies that high strength P M C

is more sensitive to elastic modulus change due to the inclusion of a "softer" phase.

Accordingly, this stiffness reduction may enable P M C (with 10 to 15%> of latex) to

withstand more deformation than normal high strength concrete.

Table 6.2 Compressive elastic modulus

Concrete type PMCO P M C 5 PMC10 P M C 15

Relative percentage of E over Plain H S C (%) 100 103.7 83.4 78.5

Relative change of E (%>) N / A +3.7 -16.6 -21.5

96

The water absorption of the different mixes showed an obvious decrease with

increasing polymer/cement ratio (Fig.6.14). The minimum value o f the 48-hour water

absorption for all of these mixes is 0.358% (PM15%), only 263% that of the plain high

strength concrete. This may be explained by the fact that some voids were fdled, perhaps

only partially, with a polymer f i lm which is always hydrophobic, leading to decreased

water absorption for P M C s . Similar tendencies have been found by other researchers [12,

65], though with much smaller absolute values because they used normal strength

conventional mortar which is more porous than concrete containing coarse aggregate. A s

well , the paste in H S C is less permeable due the lower water/cement ratio. This

significant decrease in water absorption implies that a matrix containing polymer is more

cohesive, with a smaller volume of voids relative to plain high strength concrete. Thus

higher durability, due to the lower permeability and good mechanical properties, is to be

expected.

97

Elastic modulus

50

40

30

20

10

(GPa)

PMCO PMC5 PMC10 PMC15

PMC type Figure 6.13 Effects of polymer content on elastic

moudulus of PMC

0 2.5 6 26

Time (hour) Figure 6.14 Time dependence of water absorption (wt %) of

PMC with different P/C ratio

98

6.2.5 F lexura l propert ies

6.2.5.1 Polymer modif ied concrete ( P M C )

Representative load-deflection curves for the four polymer dosages are shown in Fig.

6.15. Flexural properties of the PMCs are given in Table 6.3.

0.1 0.4 0.2 0.3 Deflection (mm)

Figure 6.15 Average flexural response of PMC and plain concrete

0.5

Table 6.3 F lexura l properties of P M C *

Descript ion Po lymer Deflection Toughness Relat ive F lexura l of concrete cement at peak Factor* toughness strength

rat io(%) (mm) (MPa) rat io (MPa)

Plain 0 0.05625 0.1138 100 6.307 PMC-05 5% 0.05567 0.1304 114.6 6.722 PMC-10 10% 0.06733 0.1661 145.9 5.550 PMC-15 15% 0.08025 0.2685 235.9 4.863

*Using JSCE-SF4 method

The results indicate that the initial slopes of the load-deflection curves for the four

mixes tended to decrease with increasing polymer content, (or with decreasing matrix

99

strength). This implies that concretes with polymer inclusions are less stiff than

conventional concretes under flexural loading. This is similar to the tendency found for

the compressive elastic modulus discussed above, because although the latex emulsion

forms a continuous f i lm after the hydration of the cement i f the polymer content is high

enough in the mix, the polymer itself is an organic material which is much softer than

concrete.

The flexural strength of P M C with 5% of polymer was similar to that of the plain

concrete. Concretes with higher polymer dosages show a decrease in strength, which

seems to be contrary to some of the findings reported in the literature [1, 12]. A lso , higher

flexural strengths than those of plain concrete have been reported in the case of normal

strength concrete. The flexural strength decrease found here may be explained by the

following observations:

1. The same water/cement ratio was used for all of the specimens used in this study;

This w i l l yield d ifferent r esults f rom t hose t ests r eported i n t he 1 iterature w hich w ere

based on maitaining the same consistency. Because of the decreased water requirement

for P M C , previous researchers have generally compared results for specimens with

different water/cement ratios, which is "unfair" to the plain mix.

2. The flexural strength of high strength concrete may be more sensitive to polymer

additions than that of normal strength concrete due to the larger decrease in stiffness.

3. The various polymers used by different researchers have different parameters

such as the chemical components, f i lm hardness, elongation at failure, particle size in

aqueous dispersions and temperature of f i lm formation [66]. This may lead to different

compatibilities between the cement and the polymers.

The deflection at failure of P M C , however, increased significantly, leading to more

than a doubling of the total toughness, although a similar failure mode to that of plain

high strength concrete was seen with the naked eye. This increase in toughness is helpful

for increasing the energy absorption of the concrete, which may increase the efficiency of

fiber reinforcement when the matrix is P M C .

100

6.2.5.2 Effects of polymer additions on F R C

It is commonly accepted that the flexural behaviour of a fiber reinforced concrete

beam can be described as consisting of three stages [6]: first, the load increases almost

linearly with the displacement up to some critical value near to the peak load, at which

the first major crack occurs. Second, either strain-softening or strain-hardening behaviour

is then observed after the first crack. The strain-hardening occurs i f there are enough

fibers, i f they are wel l anchored into concrete matrix, and i f their ability to transfer load

across cracks is higher than that of the matrix itself. That is, a multiple cracking process

occurs, due to the ease of formation of the new cracks compared to the difficulty of

propogating the existing cracks where fibers play a bridging role. The third step involves

the post-crack behaviour, which depends strongly on both the fibers and the matrix. It is

this part of the performance that is of particular interest. It represents the toughness of

the material. In what follows, a description of the above three stages for each type of mix,

together with toughness characterization using different approaches are discussed.

For ease in analyzing the effects of polymer addition on F R C , representative flexural

load-deflection curves are re-plotted in Figs. 6.16, 6.20, 6.24, 6.28, and 6.32 for the same

volume fraction of fibers. It may be seen that there is a significant influence not only of

fiber type but also o f matrix type on the flexural properties of the composites. The

following discussion deals with specific fiber types in a P M C matrix, i.e., steel fiber

reinforced concrete — S F R C , P P N fiber reinforced concrete — P P N F R C and H P P fiber

reinforced concrete — H P P F R C .

(1) P M - S F R C

Figs.6.16 and 6.20 show the flexural responses of P M - S F R C for 0.5% and 1.0% fiber

volumes, most of these load-deflection curves show a strain-hardening trend with the

incorporation o f polymer; after first crack, the flexural load still increases with increasing

deflection, displaying properties of high performance F R C (HPFRC) . The effect of

polymer additions on the Toughness Index ( A S T M C1018), P C S strength, and toughness

factor TF (JSCE SF-4) are compared in Figs 6.17 and 6.21, 6.18 and 6.22, and 6.19 and

6.23, respectively.

101

0.5 1 1.5 2 Deflection (mm)

Figure 6.16 Effects of latex on flexural response of PM-SFRC beams (Vf=0.5%)

• PMO • PM5 • PM10 • PM15

I5 110 '20 '30 '60

Figure 6.17 Toughness indices (ASTMC1018) of concrete with 0.5% steel fiber and different dosages of latex

102

6.816 6.981

4.843

P M C O P M C 5 P M C 1 0 P M C 1 5

Figure 6.19 J S C E toughness factor for beams with 0.5% steel fibers and different dosages of latex

103

0 0.5 1 1-5 Deflection (mm)

2

Figure 6.20 Effects of latex on flexural response of P M -SFRC beams (Vf=1.0%)

80 i

I 5 J-io I20 I30 *60

Figure 6.21 Toughness indices(ASTMC1018) of concrete with 1.0% steel fibers and different dosages of latex

104

re CL

— * — i

— — • -/

i

• — • - — ! < •

i - • - P M O

• P M 5

- A - P M 1 0

X P M 1 5

- • - P M O

• P M 5

- A - P M 1 0

X P M 1 5

_ . i

- • - P M O

• P M 5

- A - P M 1 0

X P M 1 5

0 0 . 2 0 . 4 0 . 6 0 .8 1 1.2 1.4 1.6 1.8 2 2 . 2

L /m ( m m )

Figure 6.22 PCS values of beams with 1.0% steel fibers and different dosages of latex

1 2

^ 1 0 re

CL

8

o to 6 (A 0 c D) 4 3 O

7T292

9 . 9 2 8

8 . 3 7 3 8 . 0 6 7

P M C O P M C 5 P M C 1 0 P M C 1 5

Figure 6.23 JSCE toughness factors for beams with 1.0% steel fibers and different dosages of latex

105

In Fig.6.16, for mixes with a relatively low volume fraction of steel fibers, 0.5%, the

three stages of flexural behaviour mentioned above are very clear. There was strain-

softening behaviour for the composite without polymer (SFRC0.5 or PM0-SFRC0.5 ) , in

which all of the released strain energy became localized at a single crack and fibers

across this crack progressively pulled out. The 5% dosage of polymer had less effect on

strain hardening than the 10%> dosage. A t a polymer dosage of 15%, the first crack load

was reduced, but beyond that point the load continued to increase with increasing mid-

span deflection.

The toughness indices determined according to A S T M C 1018 (Fig.6.17) show that

I5 and Iio are similar for all levels of polymer addition, but with I2o and I3o showing

differences due to polymer addition. These differences, however, are not very significant;

only the index I60 of PM15 (i.e., for a large deformation) is much higher than that of any

of the others. However, the J S C E and P C S methods (Figs.6.18 and 6.19) do provide a

clear differentiation: J S C E method indicates a remarkable improvement in toughness and

PCS method shows a significant increase of post crack strength when the matrix changes

from P M C 5 to P M C 10, though there is no toughness increase beyond this dosage (at

15%>). This can be explained by the balance between improved bonding and decreased

flexural strength due to the inclusion of a greater volume of a "soft" phase in the concrete

at the same water: cement ratio.

In composites with a fiber volume fraction of 1.0% without polymer modification

(PM0-SF1.0 in Fig.6.20), the post-crack curve showed a greater load-carrying capacity

than for PM0-SF0.5 . This can be attributed to the fiber contribution in carrying the loads:

After the maximum tensile stress reaches the tensile strength of the concrete matrix,

cracking occurs and the load carried by matrix is transferred to the fibers. If the number

of fibers is sufficient to carry a higher portion of the tensile force, the post-crack

performance is better than at a lower volume fraction of fibers. Further, i f both the

number of fibers and the bonding between fibers and matrix are good enough to generate

a resistance force equal to or greater than that of the matrix in the tension zone of beam,

the post-crack of load-deflection curve does not decline, leading to higher performance

characteristics of the concrete. Here, with the fiber volume fixed at 1.0%>, any changes in

flexural properties can be attributed to the polymer addition.

106

Polymers appear to increase the efficiency of steel fibers in concrete at higher fiber

volumes, thus giving these composites the characteristics of high performance F R C ( P M -

SF1.0 in Fig.6.20). A t a fiber volume fraction of 1.0%, both the peak load and the post-

crack behaviour (i.e., the toughness) were significantly improved for composites P M 5 -

SFRC1.0 and PM10-SFRC1 .0 , compared to the 1.0% S F R C mix without polymer. This

observed strain-hardening performance would be preferred for various practical structural

applications [67].

When the polymer/cement ratio reached 15%, only a marginal toughness

improvement of the S F R C was observed, similar to the case of composite PM15-SF0.5.

This implies that there is an upper bound for the latex dosage used in this polymer

system, while at the low dosage of 5% the amount of polymer was insufficiant to change

the bonding properties significantly, even though the flexural strength (peak load) was

very high.

Quite interestingly, different methods of analysis can lead to different conclusions

regarding the toughness. Toughness parameters calculated according to A S T M CI018

and J S C E SF-4 (Figs. 6.21 and 6.23) showed that all toughness indices (I5 to T 6o ) and TF

values increased up to 15% polymer addition; in this series, mix PM10-SF1.0 was

superior to the others. However, it is not easy to decide which mix is "best" using P C S

method. The results (Fig.6.22) indicate that the post-crack strengths for PM5-SF1.0 and

PM10-SF1.0 are quite similar, with the former higher than the latter up to a deflection of

0.9 mm. P C S curves for PM0-SF1.0 and PM15-SF1.0 were also similar, with the former

having a better P C S when the deflection reached 1.0 mm.

(2) P M - H P P F R C

The load-deflection curves all showed strain-softening behaviour with the

incorporation of polymers in H P P fiber reinforced concrete (HPPFRC) at 0.5% and 1.0%

fiber additions. Figs. 6.24 and 6.28 show flexural responses o f H P P F R C . The effects of

polymer additions on Toughness Index ( A S T M CI018), P C S strength and TF (JSCE SF-

4) are compared in Figs 6.25 and 6.29, 6.26 and 6.30, and 6.27 and 6.31, respectively.

107

0 0.5 1 1.5 Deflection (mm)

Figure 6.24 Effects of latex on flexural response of PM HPPFRC beams (Vf=0.5%)

I io I 20 I 30

Figure 6.25 Toughness indices(ASTM C1018) of concrete with 0.5% HPP fibers and different dosages of latex

108

1 1.2

L/m (mm)

Figure 6.26 PCS values of beams with 0.5% HPP fibers and different dosages of latex

_^2.5

a.

£ 2

o •S to w OJ c x: O) 3

o

1.5

0.5

2.233 2.252 2.104 2.152

PMCO PMC5 PMC10 PMC15 Figure 6.27 JSCE toughness factor for beams with 0.5% HPP

and different dosages of latex

109

0 0.5 1 1.5 Deflection (mm)

Figure 6.28 Effects of latex on flexural response of PM-HPPFRC beams (Vf=1.0%)

40 n

•5 IlO ho I 3 0 ho

Figure 6.29 Toughness indices(ASTMC1018) of concrete with 1.0% HPP fibers and different dosages of latex

110

4 . 0 5 4

3 . 7 8 2

3 . 2 4 8

2 . 7 7 9

P M C O P M C 5 P M C 1 0 P M C 1 5

Figure 6.31 JSCE toughness factor for beams with 1.0% HPP and different dosages of latex

111

In all of the H P P mixes, a sudden load drop was observed after the peak load

(Figs.6.24 and 6.28). The curves for PM-HPP0 .5 , regardless of the polymer content,

showed almost the same characteristics (Fig.6.24), which implies that polymers do not

have much effect on the flexural properties of H P P - F R C at low volume fractions

(Vf=0.5%).

Toughness analyses all showed very similar trends for the P M - H P P 0 . 5 series, except

for composite PM15-HPP0.5 . Quite different conclusions about this composite can be

reached from the different toughness characterizations: using the A S T M toughness index

(Fig.6.25), PM15-HPP0.5 appeared to be better than others. Obviously, however, this is

an unreasonable conclusion when one considers the load-deflection curve. The P C S

method (Fig.6.26) shows almost no difference within the PM-HPP0 .5 series, particularly

beyond a deflection of 0.2 mm. On the other hand, the sequence of enhancement due to

the polymer (from the J S C E SF-4 method, Fig. 6.27) is:

P M 5 « PM10 >PM15 > PMO

Even when more fiber was added (Vf=1.0%), a sudden load drop was also found

after peak load, but the post-crack load carrying capacity was greater than that for the

fiber volume of 0.5%. A l l of the toughness approaches showed the same trend with the

following sequence of enhancement:

P M 5 > PM10 > PM15 > PMO

In summary, it can be concluded that H P P fibers showed a lower compatibility

(compared to steel fibers) with the polymer used in this program. The optimum polymer

cement ratio was 5% from considerations of toughness.

(2) P M - P P N F R C

Polymer modification also affected the flexural properties of the F R C containing

P P N fibers. A l l P P N F R C mixes, with or without polymer additions, showed different

load-deflection responses from the mixes with steel fibers (Figs. 6.32 and 6.36). After the

composite reached the peak load, a sudden drop of load occurred, as with the H P P fibers.

The effects of the polymer on the toughness indices, TF and P C S strength are compared

112

in Figs. 6.33 and 6.37 (ASTMC1018) , Figs. 6.34 and 6.38 (PCS method), Figs. 6.35 and

6.39 (JSCE-SF4), respectively.

Results from the J S C E method (Fig.6.35) indicate that the T F of mix PM5-PPN0.5

was very close to that of the composite PM15-PPN0.5 , but both of these were much

lower than that of PM10-PPN0.5 . The P C S strength of PM10-PPN0.5 was higher than

PM5-PPN0.5 and PM15-PPN0.5 , but was lower than that without polymer (PMO-

PPN0.5) up to a deflection of 1.2 mm (Fig.6.34). Information from A S T M CI018

method was quite consistent with that from the J S C E SF-4 method. The reason why

PM05-PPN0.5 performed worse than PPNFRC0 .5 without polymer is not clear.

However, with higher dosages of polymer, the observed phenomena may be explained by

two factors:

(1) The lower strength of the P M C matrix with a higher polymer cement ratio of

15%;

(2) The improved bonding between P P N fibers and the P M C matrix, (confirmed by

examination of the cracked beams), which caused more fibers to break than to pull out.

When V f was increased to 1.0%, the mixes with a polymer: cement ratio of 5% and

10% showed a slight increase in toughness (Fig.6.39), unlike the PM-PPN0 .5 series.

Similar performance can be observed for PM15-PPN1.0 , in which the toughness tended

to decrease no matter which analysis method was used. Thus the optimum dosage of

polymer for the P P N fiber used here is about 10%.

113

Is I 10 I 20 I 30 J-60

Figure 6.33 Toughness indices(ASTMC1018) of concrete with 0.5% PPN fibers and different dosages of latex

114

3 . 5 1 9

3 . 2 2 6

2 . 6 2 7 2 . 6 5 7

P M C O P M C 5 P M C 1 0 P M C 1 5

Figure 6.35 JSCE toughness factor of beams with 0.5% PPN fibers and different dosages of latex

115

30

25

116

8

7 4

0 \ 1 ; j j i i 1 ; i 1 1 0 0 . 2 0 . 4 0 .6 0 . 8 1 1.2 1.4 1.6 1.8 2 2 . 2

L/m (mm) Figure 6.38 PCS values of beams with 1.0% PPN fibers and

different dosages of latex

CO Q.

o 3 4 42 to to 3 CD J

4.516 5 . 0 6 6

4 . 6 9 7

4 . 2 0 5

If 2 o

P M C O P M C 5 P M C 1 0 P M C 1 5

Figure 6.39 JSCE toughness factor for beams with 1.0% PPN fibers and different dosages of latex

117

(3) Summary of polymer effects on PM-FRC

Overall, the toughness characteristics of S F R C , H P P - F R C and P P N - F R C are

improved by an optimum polymer dosage of about 5-10%. The effect of the polymer is

especially significant for steel fiber reinforced concrete. The toughness improvements

due to the polymer latex at lower dosages are due to the fact that latex modification helps

the matrix not only by reducing moisture evaporation and hence reducing plastic

shrinkage cracking but also because the latex f i lm acts to bridge cracks and thus to

prevent the propagation of micro-cracks, unlike conventional concrete or mortar matrix

which is held together by relatively weak Van der Waal 's forces, and in which

microcracks develop at early ages due to the stresses induced by drying shrinkage [1].

The function of the latex f i lm is similar to that of a "micro fiber" in concrete, even

though this f i lm by itself provides only a limited contribution to toughness improvement.

However, there is a synergy when the latex is used in combination with macro fibers.

Further, the lower elastic modulus of the interface due to the addition of the latex, as

indicated by the lower elastic modulus under compressive load and the reduced initial

slopes o f the flexural curves, may be one of the factors contributing to the improved

performance. Reduced stiffness of the interface leads to an increase in the deformability

of the interface and thus some stress relaxation under load, therefore enhancing the

properties of the system.

Most important, the interactions between the fibers and the matrix are stronger

because of the latex. In other words, the bonding between fibers and matrix is enhanced.

Also, the fiber-matrix and the aggregate-matrix interfaces are not as brittle at the same

water/cement ratio as those of ordinary high strength concrete. Less brittle, but stronger,

bonds gave the composite an increased load-carrying capacity, and therefore more

ductility and higher peak loads were observed, particularly for steel fibers. Similar effects

of polymers had been observed b y Z h o n g et al.[69], who suggested that the improved

interface between steel fibers, aggregate and matrix was because the new matrix was

more cohesive than the conventional matrix, and that the latex f i lm, partially formed on

the fiber s urface, m ay function a s a b onding agent. S tudies o n P M - G F R C ( glass fiber

reinforced concrete with polymer) have also shown that coverage by a latex f i lm, even

118

partially, is helpful in increasing the bond and the durability of the glass fibers as well

[70],

6.2.5.3 Effects of f iber volume in the P M C system

Figs. 6.40 to 6.43, 6.45 to 6.48, and 6.50 to 6.53 show flexural load-deflection curves

for composites with different fiber reinforcements, where the fiber volume fraction is the

variable. Flexural Toughness (FT) comparisons based on J S C E - S F 4 are shown in Figs.

6.44, 6.49 and 6.54. The increase in toughness with increasing fiber volume (from plain

to 0.5%, and 1.0%) is shown in Table 6.4.

119

45

0 0.5 1 1.5 2 D e f l e c t i o n ( m m )

Figure 6.41 Flexural responses of beams with different fiber volume fractions (PM5-SFRC)

120

0.5 1.5 D e f l e c t i o n ( m m )

Figure 6.43 Flexural responses of beams with different fiber volume fractions (PM15-SFRC)

• M a t r i x P M C O • M a t r i x P M C 5 • M a t r i x P M C 1 0 • M a t r i x P M C 1 5

0.5%SF 1.0%SF

Figure 6.44 Toughness factors (JSCE SF-4) of PM-FRC with different Vf of steel fibers

121

Vf=0.5%

Vf=1.0%

Vf=0.5%

Vf=1.0%

Vf=0.5%

Vf=1.0%

1 0 0.5 1 1.5 2

Deflection (mm) Figure 6.45 Flexural responses of beams with different fiber

volume fractions (PMO-HPPFRC)

o

_Vf=0

Vf=0.5%

_Vf=0

Vf=0.5%

Vf=1.0%

i —


Figure 6.46 Flexural responses of beams with different fiber volume fractions (PM5-HPPFRC)

122

V f = 0

V f = 0 . 5 %

V f = 1 . 0 %

V f = 0

V f = 0 . 5 %

V f = 1 . 0 %

V f = 0

V f = 0 . 5 %

V f = 1 . 0 %

( 0 0.5 1 1.5 2


Figure 6.47 Flexural responses of beams with different fiber volume fractions ( P M 1 0 - H P P F R C )

30 t


Figure 6.48 Flexural responses of beams with different fiber volume fractions ( P M 1 5 - H P P F R C )

123

6


0.5%HPP 1.0%HPP

Figure 6.49 Toughness factors (JSCE SF-4) of PM-FRC with different Vf of H P P fibers

30

25

20

15

10

5 I

- V f = 0

• V f = 0 . 5 %

V f = 1 . 0 %

0.5 1 D e f l e c t i o n ( m m )

1.5

Figure 6.50 Flexural responses of beams with different fiber volume fractions (PM0-PPNFRC)

124

~ 2 0 /I — — -

f Vf=0

Vf=0.5%

Vf=1.0% f Vf=0

Vf=0.5%

Vf=1.0%



125

30

25

10

5

Vf=0

Vf=0.5%

Vf=1.0%

Vf=0

Vf=0.5%

Vf=1.0%

j 1 ____ ^ j vv

1 , ,




Figure 6.54 Toughness factors(JSCE SF-4 ) of PM-FRC with different Vf of PPN fibers

126

It should be noted that the toughness increases for both F R C and P M - F R C with

increasing fiber volume; the absolute values of toughness for the steel fibers are higher

than those for the two synthetic fibers, and there is an optimum P M C matrix with

approximately 10% of latex.

Polymer additions can serve the same purpose as fiber volume increases in terms of

improving toughness. The ratio of T F P M - F R C 0.5 to T F F R C I . O ( JSCE SF-4) are shown in

Table 6.4 (the individual TF data are shown in Table 6.5). Significantly, the toughness

for beams PM10-SF0.5 and PM15-SF0.5 reached 93.5% and 95.7%, respectively, of the

toughness of PMO- F R C 1.0 (steel fiber in H S C matrix without polymer modification),

while the corresponding toughness ratio of PM0-SFRC0 .5 to P M 0 - S F R C 1 . 0 was only

61.9%. Similarly for the P P N fibers, the toughness of P M 1 0 - P P N F R C 0.5 (V f =0.5% with

10%o latex) reached 77.9% that o f PMO- P P N 1.0 (PPN fiber without polymer), and 71.4%

that of PM0-PPN1.0 for the mix PM0-PPN0 .5 ; For the H P P fibers, the toughness of

PM0-HPP0.5 and PM10-HPP0.5 were 75.7% and 81% of that for PM0-HPP1 .0 ( F R C

with 1.0% fiber only).

Table 6.4 Ratio of TF P M - F R C O . 5 to TF F R C i .o (JSCE SF-4)V

Mixes with steel fibers

Ratio <%)

Mixes with PPN fibers

n O X T T7 O 1 A

Ratio (%) 100

Mixes with HPP fibers H P P F R C 1.0

Ratio (%) 100

S F R C l . O S F R C 0 5

100 61.98

P P N r K U l . U

PPNFRC0 .5

1 \}\J

71.43 HPPFRC0 .5 75.71

PM5-SF0.5 66.42 P M 5 - PPN0.5 58.17 P M 5 - HPP0.5 80.35 X. i T l v ' fcVA v • fc*

PM10-SF0.5 93.47 P M 1 0 - PPN0.5 77.92 P M 1 0 - HPP0.5 81.04 X 1V l A \S V—J ' • fc'

PM15-SF0.5 95.73 P M 1 5 - P P N 0 . 5 58.83 P M 1 5 - H P P 0 . 5 77.44

*the toughness of FRC1.0 (PM0-FRC1.0) with the same type of fiber is used as a reference

To illustrate the toughness increase due to the fibers themselves, define Ai,j as the

difference in toughness factors due to different fiber volumes in the same type of concrete

matrix. Here, we have i or j =lfor V f =0, 2 for 0.5%> and 3 for 1.0% respectively.

A 1,2 = toughness factor ( V f = 0.5%) - toughness factor (Vf = 0)

A 1,3 = toughness factor ( V f = 1.0%) - toughness factor (Vf = 0)

127

A 2,3 = toughness factor (Vf = 1.0%) - toughness factor (Vf = 0.5%>)

Relative percentages of this increase, A i,j (together with the individual TF values),

were calculated for comparison (Table 6.5). Clearly, the efficiency of adding fibers

decrease with increasing fiber volume based on the comparison of A 1,2 (TF due to the

first 0.5%) fiber) and A 2, 3 (TF due to the second 0.5% fiber), the former being

considerably larger than the latter.

Assume that each A 2,3 (the toughness increase of F R C without polymer modification

due to a fiber volume increase from 0.5% to 1.0%) is 100% for the same type of fiber.

From the data in column A 2 ,3 (also relative increase of toughness) and Figs.6.55 to 6.57,

it can be concluded that the increase in toughness was affected in a positive way for the

P M C matrices. It is clear that fibers are more effective in a P M C matrix than in a plain

high strength concrete matrix. The only exception is the case of steel fibers in the P M C 1 5

matrix, where the increase of toughness (A 2,3) is less than that in the plain H S C matrix

(only 39%) of that value due to the inclusion of another 0.5% steel fiber). The

contribution of fibers and polymers to toughness w i l l be discussed in Section 6.2.5.5.

128

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130

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Figure 6.57 A 2,3 for the PM-PPN system

6.2.5.4 Effects of f iber types — comparison of H P P with P P N and steel fibers

It is generally accepted that steel fibers perform better than a similar volume of

polymeric fibers under static loading, due to the elastic modulus difference [64].

However, amongst polymer fibers, fiber efficiency can be quite different due to surface

properties and aspect ratios, even for the same type of raw material. The question here is

which of the two synthetic fibers performed better in the same matrix, with or without

polymer additions. To answer this question, the P P N fibers were compared with the HPP

fibers. The comparisons are based on flexural toughness and post crack strength of the

different mixes with the same fiber volume fraction and concrete matrix, with and

without polymers. To make the comparison complete, data on the P M - S F R C system are

also listed along with the data on these two synthetic fibers.

Typical load-deflection plots are shown in Figs.6.58, 6.60, 6.62, 6.64, 6.66, 6.68,

6.70, and 6.72. Both composites show a sudden load drop after peak load. However, the

131

data indicate that the P P N fibers outperformed the H P P fibers based on both P C S and

JSCE methods. From P C S strengths plotted in Figs.6.59, 6.61, 6.63, 6.65, 6.67, 6.69,

6.71 and 6.73, It can be seen that the composites with P P N fibers can carry more stress at

large deflections than those with the H P P fibers. J S C E toughness factors indicate that the

total toughness increase of P P N F R C is higher than that o f H P P - F R C , as shown in

Fig.6.74.

Quite clearly, P P N fibers play a more effective role in both the H S C matrix and the

P M C matrices, without exception, in term of the J S C E - S F 4 toughness factor and P C S

method. That is, they better toughen the composites; this may be due to the larger aspect

ratio and better surface properties of the P P N fiber.

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132

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0.5 1 Deflection (mm)

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Figure 6.60 Effect of fiber type on flexural response (PMO-FRC1.0)

133

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beams (PM0-FRC1.0)

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0.5 1.5 Deflection (mm)


137

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139

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Figure 6.74 Effect of fiber type on flexural toughness (JSCE-SF4)

140

6.2.5.5 Combined effects of fibers and polymers —Synergy analysis (JSCE-SF4)

The synergy, i f any, between the fiber and the polymer is of interest as a secondary

benefit of the polymer modification of cementitious materials, even though the polymer

itself does not have a major effect on the toughness of P M C . Synergy may be defined as

occurring when the whole is more than just the sum of the parts and can be simply

expressed as follows [71]:

F (A ,B) = F(A)+F(B)+F(A)*F(B)

That is, the synergistic effects = F(A)*F(B) = F (A ,B) - (F(A)+F(B))

where " F " represent a material property as a function of two components " A " and " B " . If

these effects are negative, the contribution of the components on the material property F

may go in the opposite direction to that which we hope to achieve. On the contrary,

positive synergy may also be observed, and is clearly to be preferred.

The following analysis w i l l be helpful to an understanding the contributions of the

individual components and the effectiveness of the interactions between the different

components, i.e., polymers and fibers. In this study, a synergy analysis of flexural

toughness was performed based on the data from the JSCE-SF4 method.

Results of the synergy analysis based on toughness factor (TF) are shown in Table

6.6, where " A " represents the fibers and " B " the polymer. Both synergistic effects

(synergy values) and the synergy ratio, defined as a ratio of a specific synergy value -—

{F(A)*F(B)} to the toughness of F R C with the corresponding type of f iber—F(A), were

calculated.

As stated earlier, the polymer itself plays a smaller role in P M C than do fibers in

F R C . Clearly from the column F(B) of Table 6.6, the contribution of the latex itself to

the toughness of P M - F R C ranged from only 1.5% to 12.5% (mostly less than 3.8%o for

P M - S F R C , less than 4.9% for P M - P P N F R C , and less than 7.4% when the polymer

cement ratio was less than 15%>). For a polymer: cement ratio of 15%>, a somewhat larger

contribution was observed, with values of 10.1% and 12.5% for PM15-PPN0.5 and

PM15-HPP0.5 respectively, However, the contribution of fibers in these composites was

141

close to or more than 100% (the corresponding data in column F(A) of Table 6.6), which

means less, or even negative synergy occurred.

Thus, as expected, fiber reinforcement contributes more than polymer addition does

to the toughness of P M - F R C . For the c ombination here of steel fibers and S B R latex,

fiber reinforcement contributed 64.6 % to 93.2 % of the total flexural toughness; the P P N

fiber contributed at least 86.1% of the toughness; and the H P P fiber contributed 66.9% to

97.7%o. These percentages vary with both fiber content and polymer/cement ratio, and are

also linked to the synergy effects between fibers and polymers.

Clearly, synergy effects are different for different fiber types, as shown in Fig.6.75.

A l l composites with steel fibers showed positive synergy, while synthetic fibers only

showed positive synergy in certain conditions, e.g, PM-HPP1 .0 , P M 1 0 - P P N and PM05 -

PPN0.5. Specifically, for steel fibers at a volume fraction 0.5%, the maximum synergy

ratio reached 48.9%> at a with 15% latex content (PM15), slightly higher than the case of

PM10-SF0.5 , where the ratio reached 47.4%. At a fiber volume fraction of 1.0%, the

maximum synergy ratio of the composites reached 33.8% (PM10-SF1.0), showing an

optimum value for all of the concretes tested for PM-SF1.0 . These trends are further

illustrated in the pie chart (Fig.6.76), which shows toughness contributions due to the

three "components" fiber, polymer and synergy.

Therefore, steel fibers show more compatibility with polymer modified high

strength concrete than do synthetic fibers. These results in terms of synergy may be

explained by the relatively poor surface properties of synthetic fibers compared to steel

fibers, and the effects of different dosages of polymer on the concrete matrix itself.

142

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6.2.5.6 Hybrid macro-fiber systems in high strength concrete (HSC) and P M - H S C

Hybrid fibers systems (combinations of two or more fibers of different types and /or

geometries) may be used to try to optimize the properties of an F R C mix [64]. Previous

studies on hybrid fiber reinforced concrete have indicated that macro - macro hybrids

(i.e., fibers of the same size but different types) are not as effective as other hybrids [68].

However, in the present study, the P P N fibers were combined with steel fibers to form a

hybrid fiber system. In particular, the question was how would this hybrid fiber system

work in a P M C matrix.

To answer the question "what works and what does not?" three tentative mixes were

produced to obtain their flexural performance: PMO-hybrid (0.5SF +0.5PPN), PM15-

Hybrid (0.5SF+0.5PPN), and PM15-Hybr id (1.0SF+1.0PPN). Figs. 6.77, 6.80, and 6.83

present average load-deflection curves for these systems together with their related

counterparts. To analyze the total toughness and Post crack performance of H y - F R C

with and without polymer additions, both J S C E and P C S approaches were used. The

results were compared with the mix having the same volume of steel fibers.

With the combination of 0.5% steel fibers and 0.5%> P P N fibers without polymer

addition (Fig.6.77), there was no obvious increase in the first peak compared to S F - F R C

0.5 and P P N - F R C 0 . 5 , but the H y - F R C showed strain hardening after the first peak, and

the load-carrying capacity was close to that of S F - F R C 1.0 after the deflection reached

1.5mm. The total toughness of this mix was still less than that of SF -FRC1.0 (Figs.6.78

and 6.79), which is in accordance with the findings on other macro-poly and macro-steel

fiber reinforced concretes [68]. This is mainly due to the lower stiffness of the P P N

fibers.

When the polymer: cement ratio was 15% for the H y - F R C with 0.5%> steel fiber and

0.5% P P N fiber, the first peak was slightly reduced compared to the same H y - F R C

without polymer, but continued to strain-harden after multi-cracking occurred. It showed

better performance after the deflection reached 0.75 mm, as shown in Fig.6.80. The P C S

of this mix was higher at larger deflections and the total toughness TF (JSCE-SF-4) was

higher than that without polymer addition. Specifically, the toughness ratios, a ratio of

toughness v alues o f t he mixes w ith p olymer t o t hat o f m ix S F-FRC1.0 , i ncrease from

146

88.4% to 93.8%. Although this increase is not large, based on the previous study

(Section 6.2.1.1), a more significant increase of flexural toughness should be expected i f

the polymer is used at lower dosages (-10%). •

Similar trends were observed for the mixes (PM15-SF1.0/PPN1.0) with higher fiber

volume fractions (2%>) when 15% polymer was used in the matrix (Fig.6.83 to Fig.6.85),

the only difference from the above H y - F R C being that this fiber hybrid showed both

strengthening and toughening. Clearly, the synergy of this mix is remarkable compared

to PM15-SF1.0 and PM15-PPN1.0 . Again, the total toughness is less than that of mix

PM15-SF2.0 for the same reasons described above.

In summary, hybrid fiber reinforced concretes with two types of macro-fibers, with

or without polymer, show synergy in terms of toughness. Polymer additions yield

positive effects on H y - F R C . This may be due to the polymer itself which can be

considered as a micro-fiber in the matrix (polymer net) in addition to the improved

bonding property and lower modulus of the matrix. However, to understand in detail the

effects of polymers on hybrid fiber systems, more tests need to be done.

147

P P N O . 5 % S F O . 5 % — — H y b r i d 0 . 5 S F + 0 . 5 P P N S F 1 . 0 %

0.5 1 1.5 D e f l e c t i o n ( m m )

Figure 6.77 Flexual performance of HSC beams with hybrid fibers (PM0-Hybrid0.5SF+0.5PPN)

• 0 . 5 % P P N » 0 . 5 % P P + 0 . 5 % S F

0 . 2 0 . 4 0 . 6 0 . 8 1 1 .2 1 .4 1 .6 1 .8

L / m ( m m )

Figure 6.78 PCS for beams with Hybrid fibers (PM0-Hybrid0.5SF+0.5PPN)

148

P P N 0 . 5 S F 0 . 5 H y b r i d

0 . 5 S F + 0 . 5 P P N

S F 1 . 0

Figure 6.79 Toughness (JSCE-SF4) of hybrid fiber reinforce concrete (PMO-FRC)

3 5 !


Figure 6.80 Effects of polymer addition on load-deflection response of beams with hybrid fibers

149

P M 1 5 - S F 0 . 5 + P P N 0 . 5

P M 1 5 - S F 1 . 0

P M 0 - S F 1 . 0

- * - P M 0 - S F 0 . 5 + P P N 0 . 5

-4

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

L /m (mm)

Figure 6.81 Effects of polymer on PCS of beams with hybrid fibers (PM15-Hybrid SF0.5+PPN0.5)

9

8

7

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P M 0 - S F 1 . 0 P M 1 5 - H y b r i d

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P M 1 5 - S F 1 . 0

Figure 6.82 Effects of polymer on flexural toughness (PM15-hybrid)

150

151

14

1 2

10

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P M 1 5 - S F 1 . 0 P M 1 5 - P P N 1 . 0 P M 1 5 - S F 2 . 0 P M 1 5 -

S F 1 . 0 + P P N 1 . 0

Figure 6.85 Toughness of hybrid-FRC beams with higher volume fractions (JSCE-SF4)

152

Chapter 7 Conclusions and Recommendations

7.1 Conclusions

The aims of this research were to provide a fundamental understanding of the

flexural properties of polymer modified fiber reinforced concrete, to optimize a

high strength polymer modified concrete matrix (PMC) , to evaluate a new type of

synthetic fiber, and to study a high performance concrete system incorporating

both fibers and polymer ( P M - F R C ) in terms of toughness. Based on the

experimental investigation and toughness analyses, the following conclusions may

be drawn:

7.1.1 P M C optimization

1. Polymer latex improves the workability (slump and VeBe time)

significantly. The addition of 15% latex can produce a high strength P M C with a

water/cement ratio of 0.28 having self-compacting characteristics.

2. The water-reducing ability of the polymer is affected by the slump; it is more

effective at higher than at lower slumps. This should be considered for mix

designs or mix optimization when both a superplasticizer and a polymer are used

to obtain a particular workability together with other objectives.

3. Compressive strength reduction is more sensitive to increased dosages of

latex for high strength P M C than for normal strength P M C . To achieve high

strength concrete with latex, a suitable curing procedure is essential. The optimum

procedure is 2-day moist-curing (or under a plastic sheet) followed by 5 days in

water, and then dry curing. This achieves the necessary balance between

conditions suitable for f i lm formation and hydration o f concrete with a low water/

cement ratio.

4. The elastic modulus of high strength P M C decreased with increasing

polymer/cement ratio, which may contribute to the enhancement of the flexural

behaviour of P M - F R C in which P M C plays a role in the matrix.

153

5. The flexural strength of P M C tended to decrease with increasing

polymer/cement ratio. The P M C s still failed in a brittle manner under both

compressive and flexural loading, although a marginal increase in ductility was

observed.

6. The water absorption capacity of high strength concrete with latex

decreased significantly with inclusion of the latex. This implies a refined pore

structure and/or lower porosity for the high strength P M C , which should

improved the durability of bulk concrete as wel l as an improvement in interface

properties between paste and aggregate (or between paste and fiber for P M - F R C ) .

7.1.2 Fiber reinforced concrete and Polymer modified fiber reinforced

concrete

1. P P N fibers bought about the greatest reduction on the slump and increase

in the VeBe time of the F R C , followed by steel fiber and H P P fibers. This can be

attributed to the increased surface area of P P N fibers after they are mixed in fresh

concrete.

2. The workability of the F R C s increased to varying degrees with increasing

polymer dosage. To get a workable low w/c ratio mix, additional superplasticizer

was required for polymer: cement ratios less than 15%.

3. Steel fibers were more effective than polymeric fibers in terms of flexural

strength and toughness in F R C without polymer; the P P N fibers were more

effective than the H P P fibers.

4. Three approaches were used to analyze the flexural toughness of the mixes:

A S T M C1018, JSCE-SF4 and the P C S method. A S T M C1018 appeared least able

to distinguish properly amongst the various mixes. The "best" mix was found to

be PM10-SF1.0 , which showed high strength and strain-hardening characteristics;

this mix would be promising for structural applications of P M - S F R C . The

superior performance can be mainly explained by the observation that the

polymer-cement co-matrix increases the overall binding capacity of the cement,

154

that is, the synergistic effect of the co-matrix, while additional gains are due to the

increased ability to deform under load and relieve stress at the interface.

5. Polymer latex showed different effects on flexural behaviour depending on

the fiber type. Generally, steel fiber reinforced concretes were more l ikely to be

improved by polymer additions than synthetic fibers. The optimum dosage was

10% for S F R C and 5%-10% for P P N - F R C and H P P - F R C . Steel fibers appeared

to b e more compatible with the polymer 1 atex than the synthetic fibers. T hus,

polymer modified synthetic fiber reinforced concrete is not recommended, at least

from the toughness point of view.

6. Fibers play a dominant role in P M - F R C s , and thus the contribution of the

fibers to toughness is much larger than that of the polymer. More importantly, the

toughness increase due to increasing fiber volume in the P M C matrix is different

from that in the H S C matrix. Fibers are more efficient in the P M C matrix than in

the H S C plain matrix.

7. Toughness synergy analysis, based on the J S C E - S F 4 method, showed the

most synergy for polymer modified steel fiber reinforced concrete ( P M - S F R C ) ,

and less or even negative synergy for the synthetic fibers in P M C matrices. The

latter may be due to a greater volume of soft phase in the concrete or the relatively

weaker bond with the synthetic fibers.

8. The hybrid mix containing macro polymeric fibers (PPN) and macro steel

fibers showed improvement in flexural toughness compared to the same mix with

the individual fiber types, but it was still less than that with the same total volume

of steel fibers. Positive synergy could be seen in the presence of the polymer latex

addition. This may be because the latex f i lm, at least partially, plays the role of

"micro polymeric fiber".

155

7.2 Recommendations

The experimental program carried out here has provided a better

understanding of the properties of fiber reinforced concrete with latex

modification ( P M - F R C ) compared with P M C and F R C . However, because the

combined use of polymer and fiber is a relatively new concept, there still are a

number of areas related to the current study which need to be explored further.

The following suggestions are made for further work:

1. Different polymer types such as redispersible polymer, single component

epoxies, and so on, should be explored.

2. The synergy between steel fibers and polymer for low strength matrices

needs to be investigated.

3. To further understand the performance of P M - F R C , S E M examination of

the interface or interface hardness tests should be carried out, in conjunction with

fiber pull out tests.

4. Previous studies have shown that both F R C and P M C have good impact

resistance. To make full use of P M - S F R C , dynamic tests including fatigue tests

should be carried out.

5. More detailed and extensive studies of hybr id systems, such as macro-

fiber and micro fiber need to be carried out with a P M C matrix to understand the

synergy between fibers and polymer.

6. As one of the main advantages of polymer modification in concrete is its

excellent bonding properties to other materials, bonding between P M - F R C and a

substrate should be studied.

7. Since shrinkage is the biggest problem with repairs, a study characterizing

shrinkage cracking in the P M - F R C system is suggested.

8. Durability of concrete is a major concern. Though P M C has shown

increased durability, the durability of P M - F R C has still not been extensively

studied. Some accelerated durability tests should be undertaken.

156

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PROPERTIES OF FIBER REINFORCED CONCRETE WITH LATEX