Enhanced use of high-carbon content rice husk and sugarcane bagasse ashes in pastes and concrete through lends with a higly porous rice husk ash produced by controlled calcination

[EN] This study explores the potential of utilizing residual rice husk (RHA) and sugarcane bagasse (SCBA) ashes with high loss on ignition (LOI) in combination with a highly porous/amorphous RHA (calcination-controlled method) for the enhancement of cementitious properties. In order to do so, cement was replaced by 20 % in binary and ternary mixtures. The effects on hydration kinetics and product formation were assessed using isothermal calorimetry and thermal analysis. On concrete samples, compressive strength, total water absorption, voids index and water absorption by capillarity were evaluated. Results revealed that blending residual RHA and SCBA with high-porosity RHA eliminated the retarding effect typically associated with high-LOI ashes, and improved calcium hydroxide consumption compared to all-binary pastes. Besides, ternary concrete mixtures (OPC+residual ash+high-porosity RHA) exhibited superior compressive strength at all curing ages, outperforming binary concrete mixes (OPC+residual ash). Additionally, ternary blends resulted in denser matrix, as evidenced by lower total water absorption, reduced voids index, and decreased water absorption by capillarity. Furthermore, cluster analysis was used to identify similarities in behavior among pastes and concretes. For instance, it revealed that the paste with porous RHA exhibited distinct hydration kinetics (0% of similarity), emphasizing its accelerating effect on cement hydration reaction. Nonetheless, similarities of ~84 % (pastes) and ~68 % (concretes) were observed between blended systems with both RHAs, indicating porous-RHA enhanced homogeneity on paste/concrete properties. As a result, these findings highlight the potential of using high-LOI RHA and SCBA (considered ashes with low valorization potential) in concrete production without a detrimental effect on performance.