Compressive Strength, Hydration and Pore Structure of Alkali-Activated Slag Mortars Integrating with Recycled Concrete Powder as Binders

Recycled concrete powder (RCP) recycling can reduce the consumption of natural resources, which has been highlighted as an ecofriendly and sustainable approach. The alkali-activated slag (AAS) offers notable prospects for replacing conventional Portland cement binders. In this study, we partially replaced granulated blast furnace slag (GBFS) with RCP to prepare the AAS mortars. We evaluated the effect of RCP replacement levels and fineness levels on compressive strength, early hydration process, and pore structure pertaining to AAS mortars with RCP (RCP-AAS mortars). According to the experimental results, using 10–30% RCP inside AAS mortars enhanced the compressive strength at 1 day, and the improvement was obvious with increasing RCP fineness. The RCP delayed the early-age hydration of the GBFS, decreased the content of hydration products and increased the total porosity. Therefore, it exhibited a negative effect on 28-day compressive strength. These drawbacks of RCP however, could be modified by increasing its fineness.