Effect of rice husk ash on mechanical properties, fracture energy, brittleness and aging of calcium aluminate cement concrete

The calcium aluminate cement (CAC) is considered as eco-cement due to the reduced carbon emission during its production; it has various applications due to its high early age strength and enhanced durability in harsh environments. However, the initial hydration products of CAC concrete are temperature dependent and meta stable that will gradually convert to more stable phases. Such transition from an initial product that are dense and strong to more stable phases that are weaker and more porous, causes a reduction in strength and durability over time. This article discusses the results of a comprehensive study on incorporating rice husk ash (RHA) in CAC concrete in order to limit the phase transition of CAC hydration product and stabilize its long-term properties. Various concrete mixtures with different contents of RHA (0, 2.5, 5, 7.5, and 10%) as a cement replacement material were examined. In addition to the workability properties of the fresh concrete, the microstructural and mechanical properties of hardened concrete are characterized at the ages of 7, 28 and 90 days. The findings indicate that, at 90 days, the mechanical strengths of the mixes containing RHA were higher than those of the control mix, with the maximum improvement occurring at the substitution percentage of 5%. In accordance with TGA analysis the substitution of 5% RHA in CAC concrete led to a higher hydration level, which in turn improved the mechanical properties relative to the specimen without RHA at 90 days.