Properties of Tensile Strength of Non-Cement Concrete using GGBS binder activated by Sodium Silicate

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1 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, School of Architecture, Mokpo National University, Jeollanamdo, Korea, 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 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 =0.63 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. 763

2 In ACI code, relationship between flexural tensile strength f r and compressive strength f ck of ordinary portland cement(opc) concrete is proposed f r =7.5 (1psi=0689MPa). In CEB-FIP, relationship between splitting tensile strength f sp and compressive strength f ck is proposed f sp =0.282(f ck ) 2/ 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 GGBS Sodium Silicate Chemical Composition MgO Al 2 O 3 SiO 2 SO 3 CaO Na 2 O TiO 2 Fe 2 O SiO 2 Na 2 O mix proportions Two major variables which are water-binder ratio (W/B) and Alkali quality coefficient (Q A ) 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 Q A S/A SS SS SS Sodium Silicate SS (Na 2 SiO 3 ) SS SS SS SS

3 2.3 casting, curing and testing Concrete is mixed forcefully in a mixer of 60 litre capacity as shown in figure.1. Cylindrical test specimens of Φ100mm 200mm size dimension are produced by each age in accordance with KS F 23. The fine/coarse aggregate, source material, alkali activator are dry mixed in a mixer pan for 30second and water is then added and mixed for a Figure.1 Process of Specimen Production further 30second. Each mix is poured in steel mould to measure the compressive strength, flexural tensile strength, splitting tensile strength. Immediately after casting, all the specimens are cured at a constant temperature and relative humidity of 20±2 and 60±5%, respectively, until they are tested at an age schemed to measure compressive strength, flexural tensile strength and splitting tensile strength of concrete mixed. According to the concrete compressive strength test specification of KS F 25, compressive strength test are performed at ages of 3, 7, 28, 56, 91days. Tensile strength test are performed according to KS F 28 and KS F 2423 at ages of 7, 28, 91days. 3. Results and Analysis 3.1 Compressive Strength Table.3 gives the summary of test result of compressive strength f ck and flexural tensile strength f r, splitting tensile strength f sp of hardened concrete at different age. Compressive strength of concrete at 3days is about 80% of compressive strength at 28days. The compressive strength of concrete is high at early setting time. Table.3 Compressive strength of non-cement concrete Speci Compressive Strength Slump men 3Day 7Day 28Day 56Day 91Day SS SS SS SS SS SS SS SS Compressive Strength SS3 SS SS9 SS6 SS8 SS5 30 SS7 SS Time(days) Time(days) Time(days) Figure.2 Compressive Strength of Concrete 765

4 3.2 Tensile Strength Table.4 Tensile strength of non-cement concrete Specimen Splitting Strength Flexural Strength 7Day 28Day 91Day 7Day 28Day 91Day SS SS SS SS SS SS SS SS 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. Splitting Strength SS3 SS2 SS6 SS5 SS4 SS9 SS8 SS7 Flexural Strength SS3 SS2 SS6 SS5 SS4 SS9 SS8 SS Time(days) Time(days) Time(days) Time(days) Time(days) 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 to compare and to apply with CODE. Coefficient which expressed relationship between f r and, f sp and is defined A, Β, respectively. Coefficient A which expressed relationship between f r and expressed relationship between f sp and is ranged from to 89. Coefficient B which is ranged from to Coefficient B is increased with age. Coefficient A is smaller than 0.63(f r / of OPC). Multiple regression analysis is performed with variables. As a result, relationship between compressive strength and flexural tensile strength is compressive strength and split tensile strength is , relationship between 766

5 Table. 5 Coefficient A of Concrete Specimen A(f r / ) 7Day 28Day 91Day SS SS SS SS SS SS SS SS f r f r =0.70 f ck f ck Figure.5 Relationship between f ck and f r Table.6 Coefficient B of Concrete Speciemen B(f sp / ) 7Day 28Day 91Day SS SS SS SS SS SS SS SS f sp f sp =5 f ck f ck Figure.6 Relationship between f ck and f sp 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 f r = , relationship between compressive strength and split tensile strength is f sp = 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. 767

6 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, Li, Y. and Sun, Y., 2000, Preliminary study on combined-alkali-slag paste materials, Cement and Concrete Research, 30(6), Kivenko, P. V., 1992b, Special Slag Alkaline Cements(Kiev:Budivelnik Publisher), 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), Keun Hyeok Yang, Jin Kyu Song, Eun Taik Lee. Properties of Cementless Mortars Activated by Sodium Silicate. Construction and Building Materials, 22,