Multi-Objective Optimization of Alkali Activator Agents for FA- and GGBFS-Based Geopolymer Lightweight Mortars

Abstract

This article presents the effect of different sodium hydroxide (NaOH) concentrations and sodium silicate-to-sodium hydroxide (Na2SiO3/NaOH) ratio on the fresh and some hardened properties of lightweight geopolymer mortar (LWGM). The main components of LWGM are lightweight pumice aggregate, crushed limestone aggregate, and alkali-activated FA or GGBFS. Effectiveness of aforementioned parameters was tested in terms of variation of the workability, fresh unit weight, absorption and strength of LWGM. The curing parameters were taken from a previous study conducted by the authors. The alkaline activator is a mix of 8, 10, 12 and 14 molar (M) of NaOH solution and Na2SiO3 with the following ratios 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. Full factorial experimental program was adopted to observe strength development, water absorption and sorptivity of LWGM. Therefore, 256 data samples were obtained for strength and absorption properties. Optimum alkaline agent ratios and NaOH molarity were obtained from analysis of the experimental data using response surface method. 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 the workability and water absorption of LWGM. The strength of GGBFS-based LWGM with different NaOH concentrations and Na2SiO3/NaOH ratio is greater than that of FA-based GPLWM.