Hydro-thermal reaction according to the CaO/SiO₂ mole-ratio in silico-manganese slag

SiMn slag is a by-product of the production of ferroalloy, and has a chemical composition that could be used as a cement admixture. It is not currently being used in this way due to its low reactivity. The reason why SiMn slag shows this low chemical activity is that it becomes crystalline during slow cooling after it is discharged. In this study, rapid cooling was achieved by a water quenching method (the slag was dumped into water) so that the amorphous content would be high. Then its hydration activity was experimentally verified. Mortar-bars of ordinary Portland cement (OPC), cured under three conditions, were used as standards for comparison with those of SiMn-slag powder cured under dry-air, wet and autoclave conditions. Though the SiMn bars showed very low activity at first, they showed outstanding hydration activity after autoclaving. This indicated that using SiMn slag as a Si source for hydro-thermal reactions is appropriate. In addition, from the results of tests evaluating the optimum amount of slag proper for a hydro-thermal reaction, it was confirmed that cement of the greatest strength developed under the condition that CaO/SiO₂ at a mole-ratio of 1.0, was used to replace 83 % of the OPC.