Reactivity pozzolans from agro-industrial waste: A circular economy approach using cane biomass ashes

The partial replacement of Portland cement with supplementary cementitious materials (SCMs) is a key strategy to reduce the environmental impact of cement-based composites. This study evaluated the pozzolanic activity and performance of ashes derived from sugarcane and energy cane biomass, agro-industrial residues obtained by combustion. Stalks and leaves were calcined at 600 °C, washed to remove soluble compounds that negatively affect cement hydration and durability, and milled. The ashes were characterized by X-ray fluorescence, X-ray diffraction, thermogravimetry, particle size distribution, real specific mass, and determination of amorphous and crystalline silica. Pozzolanicity was assessed in calcium hydroxide pastes and suspensions, by thermogravimetry and electrical conductivity. In cement–ash pastes, the Frattini method and scanning electron microscopy were also performed. Mortars with partial cement replacement by mass (5 %, 10 %, 20 %), using sugarcane or energy cane ashes as well as 10 % silica fume, were tested for bulk density, water absorption, compressive strength, and accelerated carbonation. The results showed that both ashes exhibit significant pozzolanic activity, with energy cane ash presenting higher reactivity due to its greater amorphous silica content (up to 83.6 % calcium hydroxide (CH) fixation after 28 days). Mortars with 10 % cement replacement by mass achieved optimal performance: compressive strength reached 102 % of the reference mortar, while carbonation depth was reduced by up to 60 % compared to the control. These findings confirmed that sugarcane and energy cane ashes are effective SCMs, contributing to reduced carbon dioxide emissions, improved durability, and valorization of agro-industrial residues within a circular economy approach.