Investigation of Alkaline Activator ratio on Geopolymer Concrete under Ambient Curing Regime

Geopolymerisation allows the reuse and refurbishment of an extensive range of waste materials into building elements with excellent mechanical and durability properties, giving it potential as an environmentally friendly alternative to conventional concrete. In this paper, ground granulated blast furnace slag (GGBFS) was blended with fly ash (FA) to form binder content (B) and combined at different ratios with a solution of various alkaline activators (ALA) to make Geopolymer concrete (GPC). The ALA solution consisted of a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), with a stable NaOH concentration of 12 M (Molar) and a Na2SiO3/NaOH mass ratio of 2.5. The GPC mixes were prepared with different ALA/B ratios (0.33, 0.375, 0.40 and 0.42), and a constant partial GGBFS/FA replacement ratio was used. All of the mixes were cured under ambient conditions. To analyses the impact of the ALA/B ratio on the GPC, the compressive and splitting tensile strengths of hardened GPC were investigated and the density was measured at two different ages, 7 and 28 days. The experimental results showed that varying the ALA/B ratio had an influence on the compressive strength of GPC. Compressive strength was higher at an ALA/B ratio of 0.375 than at both higher and lower ratios. At this optimum ALA/B ratio, compressive strength of up to 57.76 MPa was recorded on the 28th day. Additionally, the hardened density of GPC ranged between 2203 and 2279 kg/m3. Finally, a relationship is proposed between compressive strength and tensile strength