Effect of C12A7 in steel slag on the early-age hydration of cement

Steel slag retards the early-age hydration of cement. However, the key component which plays a major role in steel slag is still unclear. In this paper, it was identified that C12A7 in steel slag plays a major role in retarding the early-age hydration of cement by selective treatment methods such as sieving, calcination, water washing and carbonation. The pure C12A7 was mixed with cement to confirm this retarding effect. Results show that the early-age hydration of C3S is significantly retarded with the increase of C12A7 content. In most of cement-steel slag composite binders, the C12A7 content is usually at a low level, and the retarding effect of C12A7 on the early-age hydration of C3S leads to prolonged setting time. When the C12A7 content is high enough, it leads to fast setting due to a large number of products with large specific surface areas produced by the rapid reaction of C12A7.