Mechanical properties and microscopic characterization of waste perlite powder as supplementary cementitious material.

In this study, we conducted a comprehensive investigation on the influence of waste perlite powder (WPP) on the various properties of mortar and paste, including slurry performance, mechanical strength, hydration products, and microstructure. Additionally, we also aimed to uncover the underlying mechanism behind these effects. It was found that WPP reduced the workability and facilitated the setting process of cement-WPP pastes. WPP decreased the mechanical strength of mortar, but it exhibited significant strength enhancement during the subsequent stages. The incorporation of WPP worsened the water absorption behavior; however, this negative effect was mitigated as the curing age of the mortar was prolonged. The drying shrinkage cement-WPP binary system was significantly improved, with the prolongation of curing age. Moreover, WPP reduced the early heat release of the binary system, which may be beneficial for reducing the temperature gradient in mass concrete. It was confirmed that WPP accelerated the transformation from AFt to AFm, promoted the formation of C-A-S-H and optimized the pore structure of the system. It was confirmed that WPP was involved in the hydration reaction, which accelerated the transformation from AFt to AFm and promoted the formation of C-A-S-H. Such results suggested that the reuse of WPP in concrete production was technically feasible owing to its high pozzolanic reactivity.