Advancements in materials development continue to drive innovations in sustainable and resource-efficient construction materials. Coconut shell ash (CSA), a byproduct of using coconut shells as fuel in industries, is a good resource to utilize because of its abundance. This study explores the potential of waste-derived coconut shell ash (CSA) as a material resource-based micro-filler for concrete, aligning with emerging frontiers in waste resource utilization. CSA was incorporated at 10% by volume as a partial sand replacement to evaluate its influence on the physical, mechanical, and thermal performance of the composite. Comprehensive chemical, mineralogical, and morphological analyses were conducted on both CSA and CSA-modified concrete.

Results show that CSA addition slightly reduced concrete density from 1.813 to 1.760 g/cm³ and increased apparent porosity and water absorption to 1.77% and 7.68%, respectively. Mechanical performance decreased moderately, with flexural strength declining from 4.60 MPa to 4.02 MPa and compressive strength from 6.76 MPa to 6.04 MPa. Thermal conductivity, on the other hand, increased from 0.451 to 0.490 W/mK, attributed to the intrinsic porous microstructure of CSA, as shown in Figure 1.

Overall, CSA incorporation significantly influences the physical and thermomechanical behavior of concrete. While the mechanical properties slightly decrease, the findings highlight the potential of CSA as a viable waste-derived resource for developing greener, low-impact construction materials, contributing to breakthrough directions in sustainable material/mineral engineering.