Design and characterisation of ternary cements containing rice husk ash and fly ash

This study explored the interaction between rice husk ash (RHA) and fly ash (FA) as partial (0%, 15% or 30%) additions in new ternary cements designed to reduce cement industry energy consumption and greenhouse gas (GHG) emissions by lowering their clinker content. To that end, the effect of the introduction of mixed RHA and FA on the pozzolanicity of the RHA-FA/lime system was assessed and its impact on the chemical, physical, rheological, mechanical, calorimetric and microstructural properties of the new ternary cements analysed. The joint use of these additions revealed mixture synergies, with an initial rise in FA pozzolanicity in the presence of RHA, although this effect declined over time. The inclusion of the RHA-FA mixture prompted changes in the pore structure of mortars that after 90 d translated into 2% lower compressive strength than the control in mortars with 15% addition and a 19% decline in materials containing 30% waste. That notwithstanding, the new cements were European standard EN 197-1-compliant for cement types II/A-M, II/B-M and IV-A. Furthermore, the mortars prepared with 15% RHA-FA released 5.67% less total of hydration than OPC and the materials containing 30% of the addition 13.54% less than the reference. In light of the foregoing, the new cements were found to be apt for use in construction, particularly in structures where large volumes of concrete are needed, for the reduction of the thermal gradient lowers the likelihood of surface cracking.