THE TRANSITION ZONE BETWEEN AGGREGATE AND TYPE-K EXPANSIVE CEMENT

In the case of expansive cement it is confirmed that the modified transition zone is responsible for improved strength of concrete. The modified transition zone contains more ettringite and a discontinuous CH film. Compared to the typical transition zone in portland cement concrete, it is obvious that the modified transition zone in expansive cement concrete would resist crack propagation and would therefore be stronger. Thus both the high concentration of ettringite and the CH grain-refinement in the transition zone satisfactorily explain why, with a given w/c ratio, concrete is considerably stronger when made with an expansive cement instead of a portland cement.