Experimental investigations on mechanical properties of normal and high strength high calcium geopolymer concrete

Abstract

lkali activated (Geopolymer) concrete is an excellent and viable alternative to Portland cement based concrete as it can be produced using industrial by-products such as Ground Granulated Blast Furnace Slag (GGBS) and fly ash (source of reactive alumino-silicates) along with less energy craving ingredients such as alkali activators. In this study, slag based geopolymeric concrete mixes of M40 and M80 grade were prepared using GGBS and fly ash in proportion of 70:30 by weight. Geopolymeric binder was activated using combination of Sodium hydroxide and Sodium Silicate. Activator modulus (i.e. SiO2 / Na2O) was maintained as 1 and Na2O was kept as 7% and 8% by weight of total binder respectively for M40 and M80 grade geopolymeric concrete mixes. Both the concrete mixes were evaluated for fresh properties of concrete (slump and air content) along with mechanical properties of hardened concrete. Performance of geopolymeric mixes was compared with two conventional concrete mixes of equivalent grade (i.e. M40 and M80) in terms of aforementioned mechanical properties. Study concludes that slag based geopolymer concrete mixes of a particular strength were developed at significantly lower total binder content in comparison to cementitious binder required for development of conventional Portland cement based concrete of equivalent strength. Early age compressive strength of normal strength geopolymeric concrete mixes is higher in comparison to conventional concrete mix. Modulus of elasticity and Poisson’s ratio of geopolymeric mixes of both normal and high grade are observed to be lower in comparison to their corresponding conventional concrete mixes of equivalent strength.

Short-term mechanical performance and flexural behavior of reinforced slag-fly ash-based geopolymer concrete beams in comparison to OPC-based concrete beams

“…For concrete mixes equivalent to M40 grade, the flexural and split tensile strength values of M40 RGC are slightly higher in comparison to M40 RCC. This observation is supported by the previous findings [30] also reported that flexural strength of alkali activated concrete is higher in comparison to flexural strengths of conventional Portland cement concrete of similar grade. However, in case of high strength concrete mixes equivalent to M70 grade, trends are opposite to the observations made for flexural and split tensile strength of mixes equivalent to M40 grade.…”

“…Modulus of elasticity of both M40 RGC and M70 RGC are observed to be lower than their corresponding conventional concrete mixes of similar grade. This observation is supported by observations of research studies carried out by past researchers [30,31,32].…”

“…This increase in flexural and split tensile strength of high strength conventional Portland cement concrete is similar to findings of Arora et.al [16,40,41] wherein it was reported that flexural strength of silica fume concrete was higher by 10-15% as compared that of Portland cement concrete for about 12-15 % silica fume addition. The addition of silica fume in concrete mix leads to reduction in the development of cracks at micro level near the interface of cement paste and unreacted cement or pozzolans [30,42,43,44,45]. Modulus of elasticity of M40RGC is about 70.00 % of modulus of elasticity of M40RCC and Modulus of elasticity of M70RGC is about 77 % of Modulus of elasticity of M70RCC.…”

“…But the intrinsic modulus of N-A-S-H gel formed in low-calcium fly ash gel based geopolymer concrete is much smaller than that of the C-S-H gel formed in cement. The lower value of modulus of elasticity for geopolymer concrete than conventional concrete can be attributed to the low intrinsic modulus of N-A-S-H gel and higher initial micro-cracks formulation in geopolymer concrete [30,31,32]. Yield point was determined visually from load deflection curve and the yield point is stage where no significant increase in load was observed and deflection was increasing continuously.…”

“…The difference in the gel systems formed in these two variation of the mixes can be attributed as a possible explanation of the observed trend which is not much significant in the normal strength concrete. Findings in the literature [30] suggests that the C-S-H gel formed in OPC concrete and the N-A-S-H gel primarily found in fly ash based geopolymer have variations in their intrinsic modulus which is well reflected in high strength concrete. The past literature has also shown the similar trends which validates the findings of this paper.…”