Hydration properties of mixed cement containing ground-granulated blast-furnace slag and expansive admixture

The hydration characteristics of mixed cement containing fine powder of blast-furnace slag and expandable material were examined by X-ray diffraction analysis, heat of microhydration, phase analysis, thermal analysis, and pore structure analysis. Unhydrated alite (C₃S, 3CaO·SiO₂) and belite (C₂S, 2CaO·SiO₂) were identified as the main hydrates in the specimens aged 1 h and 6 h, respectively, according to the replacement rate of fine blast-furnace slag powder cement. Moreover, the peak of unhydrated products decreased with increasing age (1 days, 3 days, 7 days, and 28 days). When the fine blast-furnace slag powder ratio was 10% and 20%, the peak corresponding to calcium hydroxide [Ca(OH)₂], a hydration product, tended to increase more than those at powder ratios of 30% and 40%. Considering the hydration characteristics of the mixed cement binder when applying the fine blast-furnace slag powder and expansion material, the hydration products were formed by the promotion of the reaction of unhydrated materials, which resulted in an increased amount of voids smaller than 0.05 μm. This is advantageous for high airtightness and stable drying shrinkage. In addition, ettringite, which is an expanding material that effectively acts on self-recovery, was actively formed within our samples.