Rice hush ash as supplementary cementitious material for calcium aluminate cement – Effects on strength and hydration

Abstract

Replacing part of calcium aluminate cement (CAC) with reactive rice husk ash (RHA) can directly reduce the impact of rice husk disposal on environment and lower the CO2 footprint of cement. RHA is comparable in chemical composition to silica fume, and thus has the potential to similarly improve the hydration of CAC. In the present study the development of strength and hydration of CAC with various amount of RHA was investigated. By means of calorimetry, X-ray diffraction analysis, 27Al magic-angle spinning-nuclear magnetic resonance spectroscopy, mercury intrusion porosimeter (MIP) and high-resolution scanning electron microscopy (SEM), a detailed insight on the changes of CAC hydration by addition of RHA is gained. Results indicate that RHA does not only accelerate hydration but also improve the early strength of CAC. A high dosage (60%) of RHA densifies the microstructure locally, but the dilution effect induces the decrease of strength. The formed hydrates are C-A-S-H phases with smaller size than CAH and thus a refined pore size develops. Considering the effect of RHA on strength, the amount of substitution should be less than 40%.