Effect of Alkaline Activator, Water, Superplasticiser and Slag Contents on the Compressive Strength and Workability of Slag-Fly Ash Based Geopolymer Mortar Cured under Ambient Temperature

Geopolymer (cement-free) concrete is the mostpromising green alternative to ordinary Portland cement concrete andother cementitious materials. While a range of different geopolymerconcretes have been produced, a common feature of these concretesis heat curing treatment which is essential in order to providesufficient mechanical properties in the early age. However, there areseveral practical issues with the application of heat curing in largescalestructures. The purpose of this study is to develop cement-freeconcrete without heat curing treatment. Experimental investigationswere carried out in two phases. In the first phase (Phase A), theoptimum content of water, polycarboxylate based superplasticizercontents and potassium silicate activator in the mix was determined.In the second stage (Phase B), the effect of ground granulated blastfurnace slag (GGBFS) incorporation on the compressive strength offly ash (FA) and Slag based geopolymer mixtures was evaluated.Setting time and workability were also conducted alongside withcompressive tests. The results showed that as the slag content wasincreased the setting time was reduced while the compressivestrength was improved. The obtained compressive strength was in therange of 40-50 MPa for 50% slag replacement mixtures.Furthermore, the results indicated that increment of water andsuperplasticizer content resulted to retarding of the setting time andslight reduction of the compressive strength. The compressivestrength of the examined mixes was considerably increased aspotassium silicate content was increased.