Abstract
Concrete manufactured using the SEC method─a two-stage mixing method in which primary mixing using primary water is followed by secondary mixing using secondary water─exhibits less bleeding and higher strength after curing. The SEC method was found to enhance filling ability under vibration of concrete in the fresh state, and to contribute to the reduction of variations in strength properties as well as the reduction of shrinkage cracks after curing. To elucidate the mechanism behind such performance improvements, microstructural analyses using SEM and EPMA were conducted for the quantitative evaluation of the reaction rate of cement in the paste and the transition zone at the cement-aggregate interface. As a result, the SEC method was found to contribute to the reduction of average thickness of the transition zone around aggregate. Further, reduction of transition zone thickness was determined to be linked to higher density, and thus durability, of concrete.
