The effect of waste-expanded perlite on alkali activation of ground granulated blast furnace slag

The purpose of this study was to evaluate the possibility of using ground waste-expanded perlite (WP) as a sustainable replacement for ground granulated blast-furnace slag (GGBFS) precursor in alkali-activated systems. The nature and amount of hydration products, microstructure, and compressive strength development were investigated in mixtures where GGBFS was substituted with 10, 20 and 40% by weight of WP and activated by two alkali activators: sodium carbonate and sodium hydroxide. The results show that WP can be successfully used as a partial replacement for GGBFS in alkali-activated materials. Activation by the Na₂CO₃ solution was more profitable in terms of compressive strength than NaOH, as well as the amount of water bound in the hydration products was higher. Substitution of GGBFS with 20 wt.% of WP activated with sodium carbonate resulted in a compressive strength of 93 MPa at 90 days of hydration while for the equivalent sample activated by sodium hydroxide, 29 MPa. Further incorporation of WP into Na₂CO₃ activated systems resulted in a reduction in performance development, especially at the early age. In addition to C–S–H, hydrotalcite, and three different types of carbonates in the samples activated by NaOH solution, a rich in sodium C(–N)–S–H was found.