Properties of Tensile Strength of Non-Cement Concrete using GGBS binder activated by Sodium Silicate Song, Jin-Kyu 1, a , Yang, Keun-Hyeok 2, b , Lee, Kang-Seok 1, c , Kim, Geon-Woo 1, d , Lee, Chan-Taek 1, e , Kim, Byeong-Jo 1, 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 [email protected], b [email protected], c [email protected], d [email protected], e [email protected], f [email protected]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 Q A 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 f r , 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 f r =0.63ඥf ୡ୩ If Tensile stress occurring in bottom of beam is larger than modulus of rupture f r , 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. 513
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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 [email protected], b [email protected], c [email protected], d [email protected], e [email protected], f [email protected] 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
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
Concrof 60 litCylindriΦ100mproduceKS F 2source mmixed iwater ifurther
Each
th, splitting t
erature and r
med to measu
mixed.
t specificatio
91days. Ten
91days.
ve strength frent age. Cohe compress
0 200
10
20
30
40
50
Tim
Com
pres
sive S
treng
th(M
Pa)
gth of Concret
ting, curing a
ete is mixed tre capacity ical test
mm×200mm ed by each ag2403. The fimaterial, alkin a mixer ps then adde30second.
h mix is pour
ensile streng
relative hum
ure compress
on of KS F
nsile strength
fck and flexurompressive stsive strength
40 60 80 100
SS3
SS2
SS1
me(days)0 2
0
10
20
30
40
50
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te
and testing
forcefully inas shown in
specimesize dimen
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midity of 20±
sive strength
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 .
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.
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