Investigation on strengths and hydration products of portland cement blending with dolomite powder and metakaolin at 20 °C and 60 °C

Abstract

This study aimed to understand the synergistic effect of dolomite powder (DM) and metakaolin (MK) on the strengths and hydration products of Portland cement (PC), then facilitating DM application in PC. Results showed that the combination of DM and MK improved the flexural and compressive strengths of mortars at 20 °C and 60 °C markedly. This was mainly due to that the combined effect of DM and MK improved the pore structure. At 20 °C, the incorporation of MK in the PC-DM pastes stimulated the generation of calcium carboaluminate including hemicarbonate (Hc) and monocarbonate (Mc). An increase in the MK to DM ratio resulted in the increment of Hc at the early age. At the later age, further dissolution of DM promoted the transformation of Hc to Mc. At 60 °C, hydrotalcite (Ht) was found in the pastes with low MK dosages (≤5 wt%), and Ht was mainly distributed in the DM particle surface. However, the additions of high MK dosages (≥10 wt%) restricted the formation of Ht. The lack of portlandite might be the major reason for the limitation of Ht formation. In addition, iron containing calcium carboaluminate could be identified in the PC-DM-MK system cured at 60 °C, especially with high MK dosages.