MECHANICAL PROPERTY EVOLUTION DURING AUTOCLAVING PROCESS OF AERATED CONCRETE USING SLAG .1. TOBERMORITE FORMATION AND REACTION BEHAVIOR OF SLAG

The chemical reactions in the formation of autoclaved aerated concrete (AAC) block were investigated. The samples were prepared using blast furnace slag at 180-degrees-C under saturated steam pressures for vari ous times from 1 to 128 h. Autoclaving for 1 h yielded 1.1-nm tobermor ite with higher Al substitution and lower Ca/(Al + Si) ratio than that made without slag, due to the high solubility of the slag during the initial stage of reaction. This suggests that the utilization of slag has an advantage of reducing processing time. On further reaction, the crystallinity of the tobermorite increases and its Ca/(Al + Si) ratio decreases, becoming constant after 64 h. After a long period of autoc laving, thick reaction rims are formed around unreacted slag particles , interrupting the diffusion of Ca from slag to matrix.