Influence of the levels of replacement of portland cement by metakaolin and silica extracted from rice husk ash in the physical and mechanical characteristics of cement pastes

The present research aimed to study the replacement of ordinary Portland cement (OPC) by metakaolin (MKL) and silica extracted from rice husk ashes (SRHA) in binary mixtures. To investigate the pozzolanic reactivity, thermal and microstructural analyses were performed in binary mixtures. To understand the physical effect of these blends, the packaging density was calculated according to the model of compressible packaging (MCP) and the compatibility/saturation levels of superplasticizers was studied with cementitious materials. Considering the substitution levels adopted, the results indicated that the paste with 40% of MKL provided a total consumption of calcium hydroxide to 28 days; however, the packaging density of the particles was reduced, while the compressive strength was maintained. The addition of 16% of SRHA in binary mixtures showed partial consumption of calcium hydroxide; nevertheless, this effect, together with the physical effect, led to an increase in the compressive strength for the same age.