The authors examined the influence of the preparation method of free lime-hauyne-anhydrite system expansive additive on its performance. The result showed that even though the same composition of additives were used, the expansive additive that was prepared by dispersing the above three compounds into clinker had more excellent expansion performance than the expansive additive that was prepared by mixing the same three compounds. In addition, if the preparation condition was different, the compressive strength when the same rate of expansion was given showed a large difference. It was considered that these phenomena were originated from differences in the reaction velocity of free lime and formation mechanism of ettringite.
