Abstract
The cement industry is a major producer of CO2 gas during cement production. Replacing cement by blast－furnace slag is an effective method for reducing CO2 cement gas exhaust. In this study we investigated the reaction and the microstructure of cement containing more than 70％ blast－furnace slag. We analyzed products produced from Blast－Furnace Slag（BFS）－Anhydrate（CS）－Ordinary Portland Cement（OPC）and the product’s ability to immobilize Cr（VI）with samples of various compositions and w/p, adding lime stone powder（LSP）. The hydration reaction and immobilization mechanism of Cr（VI）in this type of cement were analyzed by measuring heat of hydration by using a sandwich calorimeter. To determine, the reaction ratio of BFS, X－ray diffraction was used. The sample was observed by SEM and chemical analysis was determined by inductively－coupled plasma optical emission spectrometry. The hydrated cement products are ettringite, monosulfate, and Ca（OH）2. When the cement immobilizes Cr（VI）, monosulfate is usually formed. Monosulfate is known to exchange its SO42－ ions to Cr（VI）ions based upon a previous study. This study considers how the existence of monosulfate in the structure contributes to the immobility of Cr（VI）. For example, by adding LSP to the samples it change monosulfate to monocarbonate or hemicarbonate and hemicarbonate has the abilty of immobilizing Cr（VI）whereas monocarbonate does not. We propose that hemicarbonate has sufficient space to incorporate Cr（VI）ions into its structure more so than that of monocarbonate.
