Kaolin which is theoretically known having low reactivity during geopolymerization will be used as a source of aluminosilicate materials in this study. Current research had pretreated the kaolin via thermal, mechanical and chemical treatment before geopolymerization. Due to this concern, it becomes a challenge to directly produce kaolin geopolymer without pre-treatment. Hence addition of ground granulated blast furnace slag (GGBS) will accelerate the geopolymerization process. Kaolin-GGBS geopolymer ceramic can be prepared at low sintering temperature due to the reaction of chemical composition during the initial stage of geopolymerization. The objective of this work is to study the influence of the chemical composition in raw materials, curing temperature and sintering temperature on the sintered kaolin-GGBS geopolymer. The ratio of solid-to-liquid chosen were 1:1, 1.5:1, and 2:1 to analyze the contribution of chemical composition. The effect of curing temperature will be a study based on four different temperature, which is, room temperature, 40 °C, 60 °C and 80 °C. The last parameter chosen was the sintering temperature varied at 800 °C, 900 °C, 1000 °C and 1100 °C. The optimum ratio of solid to liquid obtained was 2:1 (SL 2) with densified microstructure. The addition of GGBS to the kaolin geopolymer slurry did not only hasten the hardening process during geopolymerization, the presence of CaO, and MgO in GGBS had accelerated the formation of nepheline, gehlenite, akermanite, and albite phase after sintering. Elemental distribution from micro-XRF investigation proves the high concentration of Ca in a localized area and uniformly distribution of Si aligned with the phase of akermanite in SL 2. The curing temperature at 60 °C had resulted the highest compressive strength after the sintering process. This is due to the densified microstructure with open pores in the structure of sintered kaolin-GGBS geopolymer. It can be clearly seen the phase transformation from as-cured to sintered geopolymer. Transformation of the main crystalline phase which is kaolinite to nepheline phase due to reaction with alkali activator. Kaolin-GGBS geopolymer was prepared with a ratio of solid to liquid 2:1 and 60 °C of curing temperature were prepared for the last parameter varied, which are sintering temperature. Sintering at 900 °C had resulted in the highest compressive strength due to the formation of densified microstructure. The formation of akermanite phase had contributed to the densification. The sintering temperature exceeds than 900 °C had led to the formation of interconnected pores due to the decomposition and vapourisation of CaCO3. Meanwhile, sintering at 800 °C indicates an incomplete geopolymerization process. Thermal analysis shows the stability of sintered kaolin-GGBS geopolymer when being exposed to 1100 °C. Therefore, it proves that kaolin can be directly used without heat treatment in geopolymer. The geopolymerization process had facilitated the stability of as cured samples to be directly sintered besides playing a significant role as a self-fluxing agent to reduce the temperature in producing sintered kaolin-GGBS geopolymer.
