Optimization of lightweight GGBFS and FA geopolymer mortars by response surface method

•Fly ash and GGBFS based geopolymer lightweight mortars were produced.•Compressive strength development of fourteen different mixtures were evaluated.•Full factorial experimental program was adopted for optimization study.•Response surface method was used as optimization technique.•The proposed optimum parameters were tested by experimental verification. In the first stage of the paper, the effect of binder content, curing temperature and curing time on the compressive strength of light-weight geopolymer mortar (LWGM) was investigated. The base materials used for LWGM are ground granulated blast furnace slag (GGBFS) and fly ash (FA). The main components of LWGM are lightweight pumice aggregate and alkali activated FA or GGBFS binder. Effectiveness of aforementioned parameters was examined in terms of variation of the compressive strengths of LWGMs. The experiments were performed on LWGM cubes under curing temperatures of 60, 80, 100 and 120°C with curing period of 2, 6, 8, 24, 48 and 72h. The alkaline activator is a mix of 12M NaOH solution with sodium silicate in ratio of 1:2.5. The ratio of alkaline solution to binder was taken as 0.50. 7 binder contents were taken between 650 to 1250kg/m3 with 100kg/m3 increment. Full factorial experimental program was adopted to observe compressive strength development of LWGMs. Therefore, 336 data samples were obtained. The second stage of the paper is to optimize those experimental parameters through response surface method. Test results indicate that the increment in the binder content increases the compressive strength of LWGM. The strength increases with the increase of curing temperature and curing period of LWGM. The experimental verification indicated a good agreement with optimized results.