The hydration, strength and deformation of Portland composite cements containing light-burnt dolomite and metakaolin

Light-burnt dolomite (LBD) as a compound magnesium oxide (MgO) expansive agent can compensate for the shrinkage of concrete effectively at early ages. However, in terms of strength, the replacement amount of Portland cement with LBD is limited due to the low reactivity of calcite in LBD. In this study, metakaolin used as a modified material was incorporated into blended cements containing LBD to improve the reactivity of calcite in the LBD. The results showed that the incorporation of LBD and metakaolin decreased the hydration heat and strengths of Portland cement at early ages, but the strength increased with increasing the mass ratio of metakaolin to LBD at later ages. In particular, the strengths of the blended cement containing 20% metakaolin and 20% LBD were even higher than those of Portland cement. This was mainly related to the formation of a compact pore structure with decreased porosity owing to the improvement of the reactivity of calcite in LBD and the pozzolanic reactivity of metakaolin. In addition, in comparison to Portland cement, the incorporation of LBD and metakaolin could produce a certain expansion due to the high hydration reactivity of magnesium oxide in LBD, and mitigated the shrinkage.