Evaluation of Age Strengths of Metakaolin Blend Pastes with Varying Fineness of Grind

The objective of the study was to evaluate the effect fineness of grind of metakaolin (MK) on age strength development of metakaolin/cement blend pastes. Five batches of metakaolin designated MK1, MK2, MK3, MK4 and MK5 were investigated. The metakaolins were each ground to three different fineness—95% passing 75 µm, 95% passing 53 µm and 95% passing 45 µm. Cement pastes containing 0 and 30% of MK were prepared at a constant water/binder ratio of 0.3. The compressive strengths of the cement pastes were determined at 2, 7, 14 and 28 days. The results indicated that the compressive strengths of the cement pastes with MK were not significantly affected by the fineness of grind of the MK between 75 and 45 µm particle sizes. The results showed that the highest compressive strengths were achieved with cement pastes that contained MK3 and MK5 which had the highest metakaolinite contents. MK1 which had the lowest metakaolinite content but the highest mullite and cristobalite contents exhibited the lowest compressive strength at all ages. Based on this study, it was concluded that the coarser MK can be utilized for partial replacement of OPC reducing grinding costs and ultimately market prize of the MK/cement blends.