Properties of Tensile Strength of Non-Cement Concrete using GGBS binder activated by Sodium Silicate Song, Jin-Kyu1, a, Yang, Keun-Hyeok2, b, Lee, Kang-Seok1, c, Kim, Geon-Woo1, d, Lee, Chan-Taek1, e, Kim, Byeong-Jo1, f 1 School of Architecture, Chonnam National University, Gwang-Ju, Korea, 500-757 2 School of Architecture, Mokpo National University, Jeollanamdo, Korea, 534-729 a jgsong@chonnam.ac.kr, b yangkh@mokpo.ac.kr, c kslnist@chonnam.ac.kr, d gwkim7210@lycos.co.kr, e tac3670@naver.com, f wwwjpnd@hanmail.net ABSTRACT

The purpose of this study is to establish the relationship between compressive strength and tensile strength for GGBS based non-cement concrete activated by sodium silicate. To accomplish this, compressive strength, splitting tensile strength and flexural tensile strength were measured in this study. Major variables in this test were alkali quality coefficient QA and water-binder ratio W/B.

Using the test results, the correlation between compressive strength and splitting tensile strength, compressive strength and flexural tensile strength were analyzed by the multiple regression analysis. Finally, equation to predict the tensile strength as a function of compressive strength was proposed similar to design code for OPC concrete. KEYWORDS: Sodium Silicate, Tensile Strength 1. INTRODUCTION

Recently, there has been a significant increase in the number of studies into GGBS- or FA-based alkali-activated binders. Through the previous research, the equation to predict the compressive strength of GGBS-based mortar activated by sodium silicate was proposed. To develop the structural material using these types of binder, various mechanical properties need to be investigated. Especially, the tensile strength is an important property in concrete design. In design code for OPC concrete, equation of flexural or splitting tensile strength is defined to be in proportion to compressive strength from various test results.

The tensile strength of concrete can also be evaluated by means of bending tests conducted on plain concrete beams. The beams normally have a 4 in(100mm) square cross section. The tensile strength in flexure, known as the modulus of rupture fr, is computed from the flexural formula M/Z, where M is the bending moment at the failure of the specimen and Z is the section modulus of the cross section. The split cylinder tensile strength usually ranges from 50 to 75% of the modulus of rupture. The difference is mainly due to the stress distribution in the concrete of the flexural member being nonlinear when failure is imminent. An approximate relationship for the modulus of rupture is fr=0.63 f

If Tensile stress occurring in bottom of beam is larger than modulus of rupture fr, cause cracks. These cracks proceed from extreme tension fibre to neutral axis just before fracture. Cracking of concrete means shortage of internal force and links directly structural safety. Therefore, tensile strength as well as compressive strength is important role in structural safety.

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In ACI code, relationship between flexural tensile strength fr and compressive strength fck of ordinary portland cement(OPC) concrete is proposed fr=7.5 f (1psi=0.00689MPa). In CEB-FIP, relationship between splitting tensile strength fsp and compressive strength fck is proposed fsp=0.282(fck)2/3-0.66. However, relationship between tensile strength and compressive strength of non-cement GGBS concrete activated by sodium silicate is not yet defined. In this study, compressive and tensile strength test is conducted according to Korean Standard to investigate the correlation of these two strengths. And relationship between compressive strength and tensile strength is made by multiple regression analysis.

2. EXPERIMENT

2.1 Materials

GGBS is an industrial by-product obtained from process of producing iron in the furnace, and this experiment used three kinds of fine powder of domestically produced GGBS. Additionally, because GGBS has the properties of latent hydraulic activity, it is added sodium silicate to activate for strength development. Calcium hydroxide is employed to develop water resistance. The chemical compositions of these materials are given in table.1. Table 1. Chemical Composition of Materials

Materials Chemical Composition

GGBS MgO Al2O3 SiO2 SO3 CaO Na2O TiO2 Fe2O3 5.2 13.8 31.5 2.8 44.4 0.18 1.0 0.53

Sodium Silicate

SiO2 Na2O 46.03 50.54

2.2 mix proportions

Two major variables which are water-binder ratio (W/B) and Alkali quality coefficient (QA) are used in this study. Table 2 refers to the details of mixing proportions for 9 different specimens. Table 2. Mixing Detail

Specimen Alkali Activator W/B QA S/A SS1

Sodium Silicate (Na2SiO3)

45 0.024995

40

SS2 50 0.024995 SS3 55 0.024995 SS4 45 0.029583 SS5 50 0.029583 SS6 55 0.029583 SS7 45 0.032685 SS8 50 0.032685 SS9 55 0.032685

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measure

casting,

60±5%,

tensile st

Accord

strength

accordin 3. Resul 3.1 Comp

Table.3splitting 3days is early set Table.3 C

Specimen

SS1 SS2 SS3 SS4 SS5 SS6 SS7 SS8 SS9

the compres

all the speci

respectively

trength and s

ding to the

test are pe

ng to KS F 24

lts and Anal

mpressive Stre

3 gives the stensile strenabout 80% o

tting time.

Compressive str

Slump 3Da

215 20.245 17.290 14.215 31.230 27.265 16.210 31.225 21.230 22.

Figure.1 P

ssive strength

imens are cu

y, until they a

splitting tensi

concrete co

rformed at

408 and KS F

lysis

ength

summary of ngth fsp of haof compressi

rength of non-

F

Compray 7Day 0 25.9 7 22.3 9 19.1 8 31.9 3 28.7 6 20.2 6 36.0 5 30.3 0 23.3

Process of Spe

h, flexural te

ured at a con

are tested at

ile strength o

ompressive

ages of 3,

F 2423 at age

test result ofardened concive strength a

cement concre

Figure.2 Comp

ressive Strength28Day 56D28.2 3324.1 2720.5 2331.7 3926.5 3221.5 2540.4 4833.6 3731.1 28

cimen Product

ensile strengt

nstant tempe

an age schem

of concrete m

strength test

7, 28, 56, 9

es of 7, 28, 9

f compressivcrete at diffeat 28days. T

ete

pressive Stren

h Day 91Day.8 35.3

7.6 28.7.4 23.5

9.9 40.72.4 32.35.0 23.38.0 45.07.7 35.88.0 27.2

tion

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Concrof 60 litCylindriΦ100mproduceKS F 2source mmixed iwater ifurther

Each

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med to measu

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91days. Ten

91days.

ve strength frent age. Cohe compress

0 200

10

20

30

40

50

Tim

Com

pres

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treng

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mm×200mm ed by each ag2403. The fimaterial, alkin a mixer ps then adde30second.

h mix is pour

ensile streng

relative hum

ure compress

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nsile strength

fck and flexurompressive stsive strength

40 60 80 100

SS3

SS2

SS1

me(days)0 2

0

10

20

30

40

50

T

te

and testing

forcefully inas shown in

specimesize dimen

ge in accordafine/coarse akali activatorpan for 30seced and mix

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gth. Immedia

midity of 20±

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F 2405, com

h test are p

ral tensile sttrength of coof concrete

20 40 60 80 100

SS6

SS5

SS4

Time(days)0

0

10

20

30

40

50

n a mixer figure.1.

ens of nsion are ance with ggregate, r are dry cond and ed for a

mould to

ately after

±2℃ and

h, flexural

mpressive

erformed

trength fr, oncrete at is high at

20 40 60 80 100

SS9

SS8

SS7

Time(days)

515

3.2 Tensile Strength Table.4 Tensile strength of non-cement concrete

The flexural tensile strength of non-cement concrete at 7 days is about 80% of strength at 91days. The splitting tensile strength of non-cement concrete at 7days is about 70~90% of strength at 91days, the splitting tensile strength is lower than flexural tensile strength. Split tensile strength of OPC concrete is about 1/7~1/10 of compressive strength as literatures proposed. Splitting tensile strength of non-cement concrete is about 1/10 ~ 1/14 of compressive strength.

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

SS3

SS2

SS1

Time(days)

Split

ting

Stre

ngth

(MPa

)

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

SS6

SS5

SS4

Time(days)0 20 40 60 80 100

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

SS9

SS8

SS7

Time(days)

Figure.3 Splitting Strength of concrete Figure.4 Flexural Strength of concrete

4. Regression Analysis 4.1 Correlation between Compressive Strength and Splitting Tensile Strength

Relationship between compressive strength and tensile strength is proposed using multiple regression analysis. Tensile strength is assumed α f to compare and to apply with CODE. Coefficient which expressed relationship between fr and f , fsp and f is defined A, Β, respectively. Coefficient A which expressed relationship between fr and f is ranged from 0.352 to 0.589. Coefficient B which expressed relationship between fsp and f is ranged from 0.290 to 0.491. Coefficient B is increased with age. Coefficient A is smaller than 0.63(fr/ f of OPC).

Multiple regression analysis is performed with variables. As a result, relationship between compressive strength and flexural tensile strength is -0.610+0.545 f , relationship between compressive strength and split tensile strength is -0.963+0.695 f .

Specimen Splitting Strength Flexural Strength

7Day 28Day 91Day 7Day 28Day 91DaySS1 2.5 2.6 2.9 3.0 3.1 3.4 SS2 2.0 2.2 2.5 2.4 2.6 2.8 SS3 1.8 2.0 2.2 2.0 2.4 2.6 SS4 2.5 2.7 3.0 3.0 3.2 3.5 SS5 2.2 2.3 2.6 2.6 2.8 3.1 SS6 1.7 1.8 2.0 2.0 2.2 2.4 SS7 2.5 2.7 3.0 3.0 3.3 3.6 SS8 2.2 2.5 2.7 2.7 3.2 3.5 SS9 1.4 1.7 2.3 1.7 2.1 2.4

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

SS3

SS2

SS1

Time(days)

Flex

ural

Stre

ngth

(MPa

)

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0SS6

SS5

SS4

Time(days)0 20 40 60 80 100

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0SS9

SS8

SS7

Time(days)

516

Table. 5 Coefficient A of Concrete

20 30 40 501.5

2.0

2.5

3.0

3.5

4.0

fr=0.70 fck - 0.96

f r(MPa

)

fck(MPa)

Figure.5 Relationship between fck and fr

Table.6 Coefficient B of Concrete

15 20 25 30 35 40 45 501.0

1.5

2.0

2.5

3.0

3.5

4.0

fsp=0.55 fck - 0.61

f sp(M

Pa)

fck(MPa)

Figure.6 Relationship between fck and fsp

5. Conclusion

Strength test of non-cement concrete is performed according to Korean Standard. Test results are analyzed using multiple regression analysis. Compressive strength and tensile strength of non-cement concrete are shown high at early age. Relationship between compressive strength and tensile strength are analyzed using multiple regression analysis. As a result, relationship between compressive strength and flexural tensile strength is fr = 0.70 f - 0.96, relationship between compressive strength and split tensile strength is fsp = 0.55 f - 0.61. Acknowledgements

This work was supported by the Grant of the Korean Ministry of Education, Science and Technology(The Regional Core Research Program/Biohousing Research Institute) and The Biohousing Research Center.

Specimen A(fr/ f ) 7Day 28Day 91Day

SS1 0.589 0.584 0.572 SS2 0.508 0.530 0.523 SS3 0.458 0.530 0.536 SS4 0.531 0.568 0.549 SS5 0.485 0.544 0.545 SS6 0.445 0.474 0.497 SS7 0.5 0.519 0.537 SS8 0.491 0.552 0.585 SS9 0.352 0.376 0.460

Speciemen B(fsp/ f ) 7Day 28Day 91Day

SS1 0.491 0.490 0.488 SS2 0.424 0.448 0.466 SS3 0.412 0.442 0.424 SS4 0.442 0.480 0.470 SS5 0.410 0.447 0.458 SS6 0.379 0.388 0.414 SS7 0.417 0.425 0.447 SS8 0.4 0.431 0.452 SS9 0.290 0.305 0.441

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References Keun Hyeok Yang, Jin Kyu Song, Kang Seok Lee,, Ashour, A. F., 2009, Flow and Compressive

Strength of Alkali-Activated Mortars. ACI Materials Journal 106-M07, 50-58. Li, Y. and Sun, Y., 2000, Preliminary study on combined-alkali-slag paste materials, Cement and

Concrete Research, 30(6), 963-966. Kivenko, P. V., 1992b, Special Slag Alkaline Cements(Kiev:Budivelnik Publisher), 19-54. Jin Kyu Song, Keun Hyeok Yang. Workability Loss and Compressive Strength Development of

Cementless Mortars Activated by Combination of Sodium Silicate and Sodium Hydorxide. Journal of Materials. 3(119), 119-127

Keun Hyeok Yang, Jin Kyu Song, Eun Taik Lee. Properties of Cementless Mortars Activated by Sodium Silicate. Construction and Building Materials, 22, 1981-1989

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