Multi-technique investigation of metakaolin and slag blended portland cement pastes

Increasing incorporation of metakaolin (MK) into field concrete mixtures necessitates careful study of the portland cement/MK hydrating systems. While a number of studies have been conducted on MK blends with cement, the current knowledge on its effect on hydration products and paste microstructure remains incomplete. This study evaluated the effect of MK on the nature of hydration products through X-ray diffraction, while the effect on microstructure was assessed by measuring porosity with nitrogen adsorption and determining nanoindentation modulus as well as volume fractions of CSH with varying packing densities. The 10MK paste hydrated for 7 days was compared to the plain ordinary portland cement (OPC) paste as well as to paste containing 52% slag (52SL). No significant effect was observed on the nature of hydration products with MK or SL addition. However, nitrogen-accessible porosity increased with MK and SL addition, the increase being larger with SL. The average indentation modulus for hydration products decreased with addition of MK and SL which corresponded to increasing nitrogen accessible pores.