Durability study of Portland cement blended with metakaolin from thermodynamic modeling

Abstract

The addition of metakaolin to Portland cement (PC) can increase chloride binding but is vulnerable to carbonation. The durability issues against such a coupled effect remain uncertain although chloride ingress and carbonation can occur simultaneously. This study investigated the effect of carbonation on chloride resistance in PC blended with metakaolin through thermodynamic modeling. The results showed that chloride binding increased with metakaolin replacement in the absence of carbonation. However, as carbonation progressed, the chloride binding decreased with metakaolin replacement. It is because (1) metakaolin substitution decreases calcium content in the binder and (2) calcite formation also leads to the lack of calcium for the later formation of Friedel's salt. Therefore, metakaolin-blended cement certainly lost chloride binding capacity with carbonation which should be carefully considered in the design of durability performance of metakaolin blended cement.