Valorization of Calcium Hydroxide-Rich Industrial Solid Wastes as Multifunctional Admixture for Enhanced Performance in Portland Cement-Fly Ash-Slag Systems

To address the slow early-age strength development common in ternary binder systems, this study developed a waste-derived Composite Functional Admixture (CPA) from calcium hydroxide-rich industrial solid wastes to enhance the performance of ternary Portland cement-fly ash-blast furnace slag (PC-FA-BFS) systems. By simultaneously supplying reactive Ca(OH)2 and anhydrite, CPA significantly accelerated early FA/BFS dissolution and hydration, yielding > 6.5% improvement in 1–3 day flexural/compressive strength and refined 3-day paste pore structure. Long-term analyses confirmed CPA maintained 56-day mechanical properties and hydration products, achieving comparable pore refinement (most probable pore size: 17.7–46.2 nm) to controls. Crucially, sulfate resistance exhibited particle-size dependency: Under 5% MgSO4 attack, CPA-D demonstrated 24% higher corrosion resistance than controls, outperforming CPA-B. Mechanistic studies revealed CPA-D’s superiority stemmed from its composition/size-modulated formation of stable sulfate phases (e.g., ettringite), enhancing durability. The CPA technology delivers triple sustainable advantages: industrial waste valorization, early-age performance enhancement, and cost efficiency, offering a viable pathway for high-stability green construction materials.