Investigation of effect of mixing procedure and alkaline solution to binder ratio on the strength of geopolymer concrete

Abstract

This paper presents research on the influence of mixing and adding extra water on the strength of geopolymer concrete blended with 10% of 43-grade OPC. Two mixing methods were investigated. NaOH flakes were added in the first method; during dry mixing, heat generated by NaOH - water reaction was used to accelerate the setting time of OPC and geopolymerisation reaction. The second method was adding NaOH solution of molarity 12 M prepared 24 h before mixing concrete. In the first method, the heat generated was insufficient, and increased molarity was needed to achieve the required heat, which proved uneconomical and unsafe for the user. Also, the compressive strength of concrete prepared by adding NaOH flakes was noted to be lower than that of concrete prepared with the addition of NaOH solution. The addition of extra water in concrete was also investigated by considering two different water-to-binder ratios. During experiments, the water-to-binder ratio was initially established as 0.25 so that excess water obtained from the mix design is assumed to be utilized by OPC, making both the water-cement ratio and water-binder ratio 0.25. And again, the water-to-binder ratio was established as 0.7 to avoid extra water in the mix design. It was observed that geopolymer concrete without extra water increased its initial strength more than geopolymer concrete with extra water. But the 28th day strength of both the concrete was observed to be almost the same. It is concluded that the mixing method and extra water influence the early gain of strength and cost of concrete.