Reusing thermoactivated waste paste/concrete powder for sustainable alkali-activated materials: Effects of thermoactivated temperature

The construction waste powder encompasses waste paste powder (WPP) and waste concrete powder (WCP), exhibiting an irregular microstructural morphology and containing mineral constituents like portlandite, C-S-H gel, calcite and quartz. Under the influence of thermal activation, certain hydrated products within construction waste powder undergo decomposition, concurrently generating new substances like CaO and C2S, which contribute to enhanced reactivity. Minerals within construction waste powder participate in polymerization reactions under alkali activation. Furthermore, alkali-activated mortar produced from thermally treated construction waste powder generate an increased quantity of C-A-S-H/N-A-S-H gel, resulting in a denser microstructure. When construction waste powder is thermally treated at temperatures ranging from 600°C to 800°C, the resulting alkali-activated construction waste powder mortar (AAWM) exhibits higher compressive strength. For example, the 28d compressive strength of AAWM prepared with WCP subjected to heat treatment at 800°C increased by 195.69 % compared to AAWM prepared with untreated WCP. With the increase in thermal treatment temperature of construction waste powder, the drying shrinkage of the resultant AAWM progressively diminishes, along with a gradual reduction in porosity and water absorption. For instance, the porosity and water absorption of AAWM prepared with WCP treated at 800°C decreased by 15.58 % and 18.67 % respectively compared to AAWM prepared with untreated WCP. At a thermal treatment temperature of 800°C, AAWM exhibits strong resistance to chloride penetration. Particularly, AAWM containing WPP outperforms that containing WCP in terms of chloride resistance. Consequently, this study reveals that alkali-activated materials prepared using thermally treated waste powder exhibit commendable mechanical and durability properties.