Effect of Metakaolin Sand on Properties of Cement Composites

The Slovak natural raw material kaolin sand containing 36 wt.% of kaolinite from Vyšný Petrovec deposit was thermally transformed at 650 °C for 1 hour to the metakaolin sand with relevant content of metakaolinite. Behaviour of cement composites having replacement of Portland cement with metakaolin sand including 0; 5; 10 and 15 wt.% of metakaolinite and water to solids ratio of 0.5 cured in water for 28 days and 90 days was studied by thermal analysis, X-ray diffraction analysis and mercury intrusion porosimetry analysis. The study concerned calciumsilica hydrate and calcium aluminate hydrate formation, portlandite dehydroxylation and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The replacement of Portland cement by metakaolin sand led to positive effect on relevant compressive strengths. The changes in microstructure involved especially reduction in portlandite content and pore structure refinement.