It was found that the self-compacting concrete added with the slowly cooled blast furnace slag powder has a better property of fluidity retention than the self-compacting concrete added with the granulated blast furnace slag powder or the lime stone powder. As for the mortar added with slowly cooled blast furnace slag powder, the greater the Blaine specific surface is, the better the fluidity retention is obtained. The fluidity retention mechanism of the ordinary portland cement - slowly cooled blast furnace slag powder system was shown to be resulted from that the initial hydration of C3A is suppressed by the thio-sulphate ion released from the slowly cooled blast furnace slag powder
