Mechanical-thermal activation of pretreated electrolytic manganese residue for P·I 42.5 cement: Performance, hydration kinetics, and sustainability

This study investigates the effects of mechanically-thermally activated pretreated electrolytic manganese residue (AEMR) on P·I 42.5 cement. Activation mechanism, workability, mechanical properties, hydration heat, kinetics, leaching toxicity, and sustainability were systematically evaluated. Mechanical activation leads to a reduction in particle size, while thermal treatment at 700°C promotes dehydration, dehydroxylation, and the formation of an amorphous phase, thus improving pozzolanic activity. The optimal activation condition is determined as 3 h of ball milling followed by calcination at 700°C for 1 h based on mortar fluidity, strength, hydration characteristics, leaching safety, and sustainability. Mortars incorporating up to 10% AEMR exhibit improved fluidity and 28 d compressive strength exceeding 50 MPa, which is slightly lower than that of P·I 42.5 cement. Both BM3 (ball milling for 3 h) and BM3-C7 (BM3 calcination at 700°C for 1 h) prolong the hydration induction period and reduce cumulative heat release. BM3 shows retarded early hydration but higher ultimate hydration heat (Q max ) due to the micro-aggregate filling effect and sufficient late-age pozzolanic reaction. Whereas BM3-C7 accelerates early hydration, characterized by higher rate constants, shorter t 50 , and a smoother phase transition, owing to the rapid reaction between anhydrite and reactive aluminosilicates. All samples follow the NG-I-D kinetic mechanism identified by the Krstulovic-Dabic model. Leaching tests confirm negligible heavy metal and NH 4 + leaching. The optimized mixtures lead to a reduction in carbon emissions by around 9%, a decrease in material costs by approximately 6%, and a 10% reduction in clinker usage, offering a sustainable approach for the large-scale EMR utilization in low-carbon cementitious materials. However, the parameters for industrial thermal activation and the long-term durability of AEMR cement necessitate further optimization and validation in field conditions.