Properties and characterization of ground granulated blast furnace slag geopolymer at high temperature exposures

Abstract

Geopolymerization process using ground granulated blast furnace slag (GGBFS) as aluminosilicate sources was performed. The utilization of GGBFS as an alternative and renewable material for Portland cement is growing due to global awareness towards environmental issues. Research on ground granulated blast furnace slag as a sole binder in geopolymer production is limited throughout the world. Hence, this study is essential to evaluate the physical and mechanical characterizations of GGBFS for the potential use in construction fields. The geopolymers paste was produced from the mixing of GGBFS powder, sodium hydroxide and sodium silicate solution. The slurry pastes were compacted in acrylic plastic and cure at room temperature for 28 days. Shortened setting times leads to higher reactivity of GGBFS, thus becomes the major limitation in this study. The aim of this study is to investigate the effect of NaOH concentration, solid-to-liquid ratio and Na2SiO3/NaOH ratio on GGBFS geopolymer compressive strength. The results exhibited that 10 M of NaOH concentration, solid-to-liquid ratio of 3.0, and sodium silicate-to-sodium hydroxide ratio of 2.5 at room temperature and cured until 28 days were the optimum mixing conditions for GGBFS geopolymers synthesis.The highest compressive strength of GGBFS geopolymer was achieved at 168.71 MPa. Calcite (CaCO3) and calcium silicate hydrate (C-S-H) appeared in GGBFS geopolymers after the geopolymerization reaction as determined by phase analysis. Functional group indentification shows the formation of more geopolymer bonding in GGBFS geopolymer at optimal mixing designs. In order to determine the correlation of the processing parameters in the formation of GGBFS geopolymer, a statistical design of experiment (DOE) was approach. The analysis of the experiment results through ANOVA revealed that solid-to-liquid ratios was the highest influenced with the result of 0.00 compared to NaOH concentration and sodium silicate-to-sodium hdyroxide ratios. The GGBFS geopolymer paste was exposed to elevated temperatures up to 1000 °C. The exposed GGBFS geopolymers samples indicated a compressive strength degradation of 8.9 MPa. In contrast, the GGBFS geopolymers samples had an increasing of compressive strength up to 19.8 MPa after being exposed at 1000 °C with the formation of crystallization phases. Despite strength increment, GGBFS geopolymer samples remained in cubic shape with no spalling occurred when exposed at high temperature. Furthermore, the formation of gehlenite, mayenite, and larnite phases exhibited rugged geopolymer surface with cavern appearance. As a conclusion, this study provides a better understanding of the properties and characteristic of GGBFS geopolymers. Hence, for future research, it is suggested to apply the GGBFS material in mortar, lightweight concrete and geopolymer foam in order to analyze the performance at high temperature environments.