Eucalyptus ash from biomass combustion for energy as a partial replacement for sand in mortars: a sustainable alternative.

This study investigated the use of eucalyptus ash (EA) as a partial replacement for sand in mortar properties. The EA underwent particle size reclassification (ERA) to match the particle size distribution of the sand used in the mortar mixtures. Properties of the mortar in both fresh and hardened states were evaluated, as well as the microstructure of the mortars, with substitution levels of 15%, 30%, and 50% of sand by ERA. The experimental programme included the physical and chemical characterisation of eucalyptus ash and its derivatives, including X-ray diffraction (XRD), scanning electron microscopy (SEM), consistency index, density in fresh and hardened states, capillary absorption, immersion absorption, and compressive strength. The results indicated that EA has a crystalline nature with high hygroscopicity. The reclassification process significantly reduced carbonate and pulverulent material content in the ash. Mortars with ERA tended to have more voids and absorb more water than the control. However, the compressive strength of the mortars with ERA showed similar values to the control at 7 and 28 days of curing, reaching values of 48.55 ± 0.77 MPa and 46.44 (± 0.44) MPa for 30% and 50% of ERA substitution at 28 days, respectively. Therefore, ERA provided the production of mortars with higher sustainability, with replacements of 15% and 30% being the most recommended, without significant loss in properties in the fresh and hardened state of the mortar.