Mechanical and mineralogical performance of sustainable cement composites with calcined palm oil leaf and calcined pine leaf Ash as supplementary cementitious materials

The construction sector exerts a profound environmental burden, largely attributable to cement production, which represents a major source of global carbon emissions. In pursuit of sustainable alternatives, this study explores the utilisation of agricultural by-products specifically calcined palm oil leaf ash (POLA) and calcined pine leaf ash (PLA) as novel supplementary cementitious materials (SCMs). Both ashes, when thermally processed, exhibit considerable potential to enhance the mechanical performance and sustainability of cementitious composites. An experimental programme was undertaken to evaluate mortars incorporating 5-30% POLA or PLA, in 5% increments, as partial cement replacements. Mechanical, microstructural, and phase-characterization studies were performed on both fresh and hardened states. Results demonstrated that high replacement levels of PLA (30%) severely compromised compressive strength, With reductions of 72.27%, 69.87%, and 67.64% at 7, 14, and 28 days, respectively. By contrast, equivalent POLA mixtures exhibited more moderate declines of 43.54%, 32.05%, and 32.72% over the same periods. At low incorporation (5%), both ashes fostered compact, homogeneous microstructures enriched in calcium silicate hydrate gel, reflecting robust pozzolanic activity and accelerated hydration. X-ray diffraction and Fourier-transform infrared spectroscopy confirmed these observations, revealing depletion of calcium hydroxide phases and significant modifications in Si-O-Si and O-H vibrational bands at optimal substitution levels. Conversely, excessive ash loadings impeded hydration, with persistent residues, peak broadening, and attenuated CH intensities. Overall, this study demonstrates the valorisation of calcined POLA and PLA as previously unreported SCMs, establishing their potential to reduce cement's carbon footprint while maintaining microstructural integrity and mechanical viability at optimal dosages.