Mix optimization and experimental evaluation of lightweight geopolymer mortars

The main purpose of this thesis is to propose a comprehensive procedure to obtain optimum mixture proportions for lightweight geopolymer mortar (LWGM) through experimental evaluation and analytical optimization method. In the first stage of the study, the effect of binder content, curing temperature and curing time on the compressive strength of LWGM were 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 oC with curing period of 2, 6, 8, 24, 48 and 72 h. The alkaline activator is a mix of 12 M 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 1250 kg/m3 with 100 kg/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 study is to optimize those experimental parameters through response surface method (RSM). 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. The third stage of the study is to examine the effect of different sodium hydroxide concentration and sodium silicate to sodium hydroxide (Na2SiO3/NaOH) ratio on the workability and strength properties of LWGMs. Moreover, this stage covers another optimization study by RSM. The experiments were performed on LWGM cubes under curing temperatures and curing periods obtained from optimization study in the second stage. The alkaline activator is a mix of 8, 10, 12 and 14 M NaOH solutions with sodium silicate in ratio of 1:0.5, 1:1, 1:1.5, 1:2 and 1:2.5. The ratio of alkaline solution to binder was taken as 0.50. A fixed binder contents were taken 950 kg/m3 for the base materials. Test results indicate that the increment in the Na2SiO3/NaOH ratio up to an optimum value increases the strength and decreases water absorption of LWGM. The increment in NaOH concentration from 8 to 14 M increases the strength and decreases water absorption of LWGM. The strength of GGBFS-based LWGM with different NaOH concentration and Na2SiO3/NaOH ratio is greater than that of FA-based LWGM.