Effect of low temperature calcined electrolytic manganese residue on the early-age hydration of cement paste

Low temperature calcination is an appropriate method to pretreat the electrolytic manganese residue (EMR). 180℃ is selected as an optimal temperature to apply to the present study, since the hemihydrate gypsum formed at 180℃ can improve the reactivity of EMR at no expense of considerable energy consumption and environmental pollution. This study examines how 180 °C-calcined EMR affects the composition of the pore solution and solid phases of cement paste as well as the hydration kinetics at early ages. The results indicate that the inhibition of EMR on the early-age hydration of cement paste mainly results from the dissolution behavior of hemihydrate gypsum in 180℃-calcined EMR during the 6 h-12 h period. A large-scale dissolution of hemihydrate gypsum after 6 h, released from EMR, leads to an increased Ca and S concentrations at the expense of a postponed consumption of gypsum, thus a reduced C3A reaction and a lower ettringite formation rate. In addition, the adding EMR significantly decreases the degree of pore solution in supersaturated state concerning portlandite (CH) and calcium silicate hydrate (C-S-H) gel during the 6 h-12 h period, thus hindering the early formation of hydration products by an inhibited C3S reaction. Moreover, the inhibition mechanism of 180℃-calcined EMR during the 6 h-12 h period is further emphasized on the early-age hydration.