Effects of metakaolin and nano silica on the compressive strength and microstructure of cement mortar

Abstract

This study examines the effects of metakaolin (MK) and nanosilica (nS) on the setting time, compressive strength, and microstructure of cementitious binders and cement mortar. Portland cement PC40 was partially replaced with MK at levels ranging from 5% to 20% by mass of the binder, while nS was added at concentrations of 0.25% to 0.75% in mixtures containing 10% MK. The results revealed that the inclusion of 10% MK boosted the 28-day compressive strength of the hardened binder from 50.98 MPa to 60.35 MPa. For cement mortar, the mixture with 10% MK and 0.25% nS achieved the highest 28-day compressive strength of 69.65 MPa, which is approximately 16.8% higher than the control mixture. Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) observations indicated a relatively dense microstructure, as well as the presence of silicon (Si) and aluminum (Al)-rich regions in the MK-nS-modified mortar. These findings suggest that an appropriate combination of MK and nS can enhance both the compressive strength and the microstructure of cement mortar.