Thin fly ash/ ladle furnace slag geopolymer: Effect of elevated temperature exposure on flexural properties and morphological characteristics.

The flexural properties and thermal performance of 10 mm-thin geopolymers made from fly ash and ladle furnace slag were evaluated before and after exposure to elevated temperatures (300 °C, 600 °C, 900 °C, 1100 °C and 1150 °C). Class F fly ash was mixed with liquid sodium silicate (Na 2 SiO 3) and 12 M sodium hydroxide (NaOH) solution using aluminosilicate/activator ratio of 1:2.5 and Na 2 SiO 3 /NaOH ratio of 1:4 to synthesise thin fly ash (FA) geopolymers. 40 wt% of ladle furnace slag was partially replacing fly ash to produce fly ash/slag-based (FAS) geopolymers. Thermal treatment enhanced the flexural strength of thin geopolymers. In comparison to the unexposed specimen, the flexural strength of FA geopolymers at 1150 °C and FAS geopolymers 1100 °C was increased by 161.3% to 16.2 MPa and 208.9% to 24.1 MPa, respectively. A more uniform heating was achieved in thin geopolymers which favoured the phase transformation at high temperatures and contributed to the substantial increase in flexural strength. The joint effect of elevated temperature exposure and the incorporation of ladle furnace slag further improved the flexural strength of thin geopolymers. The calcium-rich slag refined the pore structure and increased the crystallinity of thin geopolymers which aided in high strength development. [Display omitted] • Thermal treatment enhanced the flexural strength of 10-mm thin geopolymers. • FA geopolymers increased flexural strength by 161.3% to 16.2 MPa at 1150 °C. • FAS geopolymers increased flexural strength by 208.9% to 24.1 MPa at 1100 °C. • Uniform heating was achieved in thin geopolymers, aided the phase transformation. • Ca-rich LFS refined the pore structure and increased geopolymers' crystallinity. [ABSTRACT FROM AUTHOR]