Urban waste to construction material: Casuarina equisetifolia cone ash in coating mortars

This study investigates the potential use of Casuarina equisetifolia cone bottom ash (CC-BA) as an additional material in rendering mortars for wall and ceiling applications. A bibliometric analysis revealed a significant lack of research on the topic. Casuarina cones, widely dispersed in urban areas, pose a public maintenance burden but can be used as fuel, producing ash with potential applications in construction. Mortars were prepared with a 1:6 cement-to-sand ratio, incorporating 5 to 25% CC-BA by weight relative to the mass of cement, in addition to a reference mix (CPII-00). The materials underwent physical, chemical, and microstructural characterizations. Fresh-state testing indicated satisfactory workability up to 15% CC-BA, with CPII-10 yielding the best results. All compositions met the consistency index requirements, although water demand increased with higher CC-BA content. Calorimetry results highlighted CPII-05 and CPII-15 as thermally satisfactory, indicating accelerated hydration kinetics. Air content decreased with CC-BA addition, suggesting a filler effect. After 28 days, mechanical strength remained favorable up to CPII-15. Water absorption and void index increased with 20-25% CC-BA, while lower contents showed comparable or improved values relative to CPII-00. Microstructural analysis, particularly via micro-computed tomography (μ-CT), confirmed the filler effects of CC-BA, enhancing performance up to CPII-15. Overall, CPII-10 demonstrated the most promising balance of properties, with CPII-15 also suitable for the proposed applications.