MASTER'S THESIS DEFENSE PRESENTATION (Sept 16)

US Army Corps of Engineers

BUILDING STRONG®

Innovative solutions for a safer, better worldBUILDING STRONG®

Background: The State of the Art &

Path Moving Forward Issues Surrounding Portland

Cement Concrete

► Reduced Carbon Footprint

► High Firing Temperature• Approximately 1400°C

Alternative Binding Materials

► Geopolymers

Motivations

► Weak Chemical Bonding

► Corrosion Mitigation

2

Figure 1. Corrosion of steel reinforcement bar

(courtesy of buildingfacades.com)

Figure 2. “The Concrete of Tomorrow.” By-

products of other processes and materials

serving as reasonable alternatives to PCC.

(courtesy of civilengineeringforums.com)


Scope of Current Research

Previous Research Efforts

► Weiss et al. (2009)

► Allison et al. (2012)

► Moser et al. (2013)

Objective of This Study

► Study interaction between novel

enamel coatings and various

geopolymeric matrices

3

Vitreous Enamel

Pozzolanic Materials

Novel Material

Figure 2. Vitreous

enamel coated pin

(courtesy of Moser

et al. (2013)

Figure 1. Test rods having cement

applied to melted glass at the

surface of the rods (courtesy of

Weiss et al. (2009)


Materials Utilized During This Research Fiber Types

► Straight

• Fibercon International

CAR-25-CDM

► Kinked

• Dramix ZP 305

► Undulated

• Nycon-SF Type V High

Performance Steel Fiber

Coatings

► Ferro SI-677 A Black Ground

Coat

Matrix Materials

► Fly Ash

► Metakaolin

► Portland Cement

4

Figure 1. CAR-25-CDM

(straight fibers)

Figure 3. Dramix ZP 305

(kinked fibers)

Figure 2. Type V High Performance

(undulated fibers)

Figure 4. Matrix materials were fly ash (left),

metakaolin (middle), and portland cement (right)


Specimen Preparation: Application

of Reactive Vitreous Enamel Coating

5

Fibers were cleaned using ethyl alcohol to remove oils and impurities

Fibers then dipped in fresh enamel for a vitreous coating. Afterwards, pozzolans were applied for RVEC fibers.

Placed in furnace at 811°C for 2.5 minutes to harden to coating


Specimen Preparation: Embedment

of Coated and Uncoated Fibers

6

Coated and uncoated fibers mounted onto fiber platform

Mounting cups filled with fresh

mortar and fibers embedded

Fiber embedded specimens cured

for 28 days


Experimental Methods: Mechanical

& Chemical Characterization

Pullout Testing (mech.)

Push-out Testing (mech.)

Scanning Electron

Microscopy (SEM)

Energy Dispersive X-ray

(EDX) (chem.)

7


Experimental Methods: Fiber Pullout

Testing Instron 4206 30k Universal

Testing Machine

► 1kN Load Cell

Pullout rate of 0.05 inch min-1

(0.021 mm sec-1 )

Failure of fibers prior to failure of

the bond between the fiber and

matrix

Push-out testing was then

considered as a potential

alternative.

8

Figure 1. Overall setup

employed to perform

pullout testing

Figure 2. Fiber remaining in

grips of Instron machine

once the pullout test had

concluded


Experimental Methods: Push-out Testing

Fiber Push-Out Test

9

A mechanical test performed to measure the

matrix/fiber interface de-bonding energy and the

effects of frictional sliding between the matrix and

the fiber.


Experimental Methods: Push-Out

Testing (cont.)

10

Struers DuraScan-70 Fully

Automatic Hardness Tester

► 0.098 N (10 gf) to 98.10 N (10 kgf)

load capacity

Interface 1500 Low Capacity

LowProfile™ Load Cell

► 250 N load capacity

Aluminum Platen

ecos Workflow software

package

MicroPunch data acquisition

script (developed by ERDC

personnel)Struers DuraScan-70

hardness tester

Interface 1500 Load Cell

(blue) with aluminum platen

mounted atop (silver)



Testing (cont.)

Determine the site where

testing will be conducted

Push-out test is perform on the

fiber at the center of a sample

Verification of push-out by

visual inspection

11

Specimen during Push Out

testing

Specimen after testing


Experimental Methods: SEM and

EDX Spectroscopy

Polished sample

► Requires special

preparation

FEI Nova NanoSEM 630

field emission SEM

► 15 kV voltage source

► Backscattered electron

detector

Bruker Quantax AXS

solid-state EDX detector

12


Results & Discussion: Pullout

Testing

13

Comparison of the pullout testing results of

uncoated and coated kinked fibers embedded

in metakaolin and fly ash-based geopolymer

mortars.

Comparison of the pullout testing results of

uncoated and coated undulated fibers

embedded in metakaolin and fly ash-based

geopolymer mortars.


Results & Discussion: Pullout Testing (cont.)

14

Comparison of the pullout testing results of uncoated and coated

straight fibers embedded in metakaolin and fly ash-based

geopolymer mortars.


Results & Discussion: Optical

Microscopy of Fibers Post-Pullout Test

15

An uncoated straight fiber that had been

embedded in fly ash-based geopolymer

mortar and pulled out completely during

pullout testing.

A reactive vitreous enamel coated kinked

fiber that had been embedded in fly ash-

based geopolymer mortar and exhibited

necking during pullout testing.



Microscopy of Fibers Post-Pullout Test

(cont.)

16

A reactive vitreous enamel coated undulated fiber that had been embedded in

fly ash-based geopolymer mortar and exhibited necking during pullout testing.

(a) Flat, rigid side of the undulated fiber and (b) the undulated, smooth side of

the same fiber.

a b


Small Study: Tensile Tests Performed on

Each Fiber Type Under Various Treatments

Three treatment

configurations

► Untreated (no heat)

► Annealed (811ºC)

► Quenched in tap water

immediately following

heat exposure (811ºC)

Exposure to heat resulted in

approximately 40 – 60%

decrease to tensile strength

for each fiber type.

17


Lessons Learned from Pullout

Testing…

18

• Not the most efficient method of

evaluating bond strengths

• Heat exposure decreased fiber

tensile strengths

• Fibers failed prematurely

• Evident by necking of fibers

• Find an alternative technique of

evaluating bond strength


Results & Discussion: Push-Out

Testing

19

Uncoated straight fibers embedded in fly ash-based geopolymer

mortar that has undergone push-out testing.

Reactive vitreous enamel coated straight fibers embedded in

fly ash-based geopolymer mortar that has undergone push-

out testing.

Fly Ash Specimens, Uncoated, 1.0 mm Fly Ash Specimens, Coated, 1.0 mm


Results & Discussion: Push-Out

Testing (cont.)

20

Note the change in behavior of curves a & b versus that of curves c & d.

a

b d

c



Microscopy of Push-Out Specimens

21

An uncoated straight fiber embedded in metakaolin-based

geopolymer mortar that has undergone push-out testing.

A reactive vitreous enamel coated straight fiber embedded in

metakaolin-based geopolymer mortar that has undergone

push-out testing.


Results & Discussion: Avg. Bond Strengths of Fibers

(Fly Ash-Based Geopolymer Mortar)

22

0.00

5.00

10.00

15.00

20.00

25.00

1.00 1.50 2.00

Avg

. B

on

d S

tre

ng

th (

MP

a)

Sample Thickness (mm)

Uncoated Fibers

Coated Fibers


Results & Discussion: SEM Imaging of Sample

(Metakaolin Coated)

23

Overview of metakaolin-based geopolymer mortar

(200x mag.)

Interface between metakaolin-based geopolymer paste and

sand particle

(1,000x mag.)



(Metakaolin Coated) (cont.)

24

Reactive vitreous enamel coated fiber

(Overview of entire site of embedment)

(200x mag.)

Matrix-coating Interfacial Transition

Zone (ITZ) of a coated fiber

(1,000x mag.)

Microcracking at the matrix-coating ITZ

of a coated fiber

(4,000x mag.)



(Metakaolin Coated) (cont.)

At the matrix-coating interface,

pronounced chemical shrinkage is

observed.

Shrinkage is not isolated only to

this interface. This characteristics

to prevalent throughout the entire

matrix.

This shrinkage is the main reason

for the decreased bond strength

values.► The shrinkage cracking is effectively

de-bonding the coated fiber from the

metakaolin matrix at the interface.

25

Chemical Shrinkage Crack

Metakaolin Matrix Vitreous Enamel


Results & Discussion: Energy Dispersive X-ray

(EDX) Spectroscopy

(Metakaolin Specimen)

26

Line scan and elemental mapping of Matrix-Enamel-

Fiber Interfacial Transition Zones (ITZs)



(Cement Coated)

27

Straight Steel FiberVitreous

EnamelReactive Topcoat

(cement)

The image above is an expanded

view of the portland cement control

matrix.



(Cement Coated) (cont.)

28

Fiber-Vitreous Enamel Interface

Straight Steel Fiber Fiber-Enamel

InterfaceVitreous Enamel

Reactive Vitreous Enamel-Cement Matrix

Interface

Vitreous Enamel

Reactive

Vitreous

Enamel CoatingCoating-Matrix

Interface

Portland

Cement Matrix



(EDX) Spectroscopy

(Cement Specimen)

29

Line scan and elemental mapping of Matrix-Enamel-Fiber

Interfacial Transition Zones (ITZs)



(Fly Ash Coated)

30

Overview of fly ash-based geopolymer mortar matrix

(200x mag.)

Reactive vitreous enamel coated fiber (Overview of entire

site of embedment)

(200x mag.)



(Fly Ash Coated) (cont.)

The white particles throughout

the enamel have elemental

compositions consistent with

that of chromium.

► Chromium oxide particles

The appearance of separation

at the Enamel-Matrix ITZ is

actually less than perfect

polishing.

31



(EDX) Spectroscopy

(Fly Ash Specimen)

32

Line scan and elemental mapping of Fiber-Enamel-

Matrix Interfacial Transition Zones (ITZs)


Results & Discussion: Energy Dispersive

X-ray (EDX) Spectroscopy

33


Conclusions Reactive vitreous enamel coating enhances bond strength on

the order of up to 5.7 times

EDX spectroscopy shows smoother transitions in elemental

composition across the ITZs of coated specimens, translating to

these higher bond strengths

Overall toughness is increased in cementitious samples

containing coated fibers versus those with uncoated fibers

Higher standards of deviation in coated samples are as a result

of the non-uniformity of the coating

Overly thick coating negates mechanical anchorage in fibers of

deformed geometries

34


Future Work

Nanomechanical

characterization of

reactive vitreous enamel

coated fibers

Uniform application of

coatings to fiber

reinforcement

Effects of pore size

distribution on bond

strength

35

Nanoindentation of ITZ between fly ash-based geopolymer and

steel (courtesy of Allison et al. (2015))


Acknowledgements

U.S. ERDC Personnel

Dr. Charles A. Weiss, Jr., GSL

Dr. Robert D. Moser, GSL

Henry Blake, ITL

Kevin Torres-Cancel, GSL

Brett A. Williams, GSL

Jason Morson, GSL

Wendy Long, GSL

Stephen Murrell, GSL

Jackson State Personnel

Dr. Lin Li

Dr. Fashard Amini

Dr. Wei Zheng

Shanetta Cristler

36

I’d like to thank the ERDC 6.1 Military Engineering Basic Research

Program for providing the funding necessary to execute the research

presented herein.


Thank You For Listening!

Questions???

Comments???

37



Testing (cont.)

Using the EcoWorks software,

center the platen underneath

the Overview Camera (OC).

After naming the sample and

indicating testing parameters

(i.e. load), use the Evaluation

Camera (EC) to focus and find

center of hole in platen.

The hole was drilled in an

effort to insure that the bottom

of a fiber isn’t obstructed

during push out testing.

38

Evaluation Camera view of the center of hole in platen


Push Out Test Procedure Overview

(cont.)

The EC is then raised and the

push out specimen is placed

on the platen with the fiber

positioned over the hole.

Afterwards, the site of

indentation is established

using the program. Should be

as close to the center as

possible.

39

Evaluation Camera view of the center of

a fiber.

Overview of push-out test setup

including a sample prepared for testing.



(Metakaolin-Based Geopolymer Mortar)

40

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

1.00 1.50 2.00

Avg

. B

on

d S

tre

ng

ths

(M

Pa

)


Uncoated Fibers

Coated Fibers



(Portland Cement Mortar)

41

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

1.00 1.50 2.00

Avg

. B

on

d S

tre

ng

ths

(M

Pa

)


Uncoated Fibers

Coated Fibers

Documents

MASTER'S THESIS DEFENSE PRESENTATION (Sept 16)