Sustainable Cementitious Materials: A Review of the Use of Palm Tree Ash and Titanium Dioxide Sludge in Concrete

The increasing demand for sustainable construction materials has driven extensive research into the partial replacement of cement with waste-derived supplementary materials. This review examines the feasibility of utilizing palm tree ash and titanium dioxide sludge as alternative cementitious components in concrete. Palm tree ash, obtained from biomass residues, is rich in silica and exhibits pozzolanic activity, while titanium dioxide sludge, an industrial byproduct, contributes filler and nucleation effects that promote microstructural densification. The review synthesizes experimental findings on the physical, chemical, and mineralogical characteristics of these materials and evaluates their influence on both fresh and hardened concrete properties, including workability, compressive strength, durability, and long-term performance. Key mechanisms such as pore structure refinement, secondary calcium silicate hydrate (C–S–H) formation, and the synergistic benefits of combined incorporation are comprehensively discussed. Challenges related to ash processing, variability in sludge composition, and effective dispersion techniques are highlighted, along with existing research gaps that limit large-scale adoption. Overall, the review concludes that, when optimized in blended systems, palm tree ash and titanium dioxide sludge can reduce cement usage, enhance environmental sustainability, and improve mechanical performance. Future research should prioritize advanced material characterization, performance-based mix design strategies, and comprehensive service-life assessments to enable their broader application in sustainable concrete production.