<p>The widespread use of firewood in blacksmith forges, dairy processing plants, indoor heating systems, and food industries in Nepal generates large quantities of wood-based charcoal ash powder (WBCAP), which is commonly discarded as waste and presents environmental management challenges. To address this issue, this study evaluates the feasibility of using WBCAP as a partial cement replacement and examines its effects on the physical, mechanical, and durability properties of concrete. A control mix with a water–cement ratio of 0.48 (cement: sand: coarse aggregate = 1:1.44:3.03) was prepared, and cement was replaced with WBCAP at 0%, 5%, 7.5%, 10%, and 15% by weight. Tests were performed to assess workability, density, compressive strength, flexural strength, splitting tensile strength, and water absorption. The results indicate that 7.5% WBCAP provides optimal performance, enhancing 28-day compressive, flexural, and splitting tensile strengths by 8.9%, 7.1%, and 11.7%, respectively, with comparable gains also achieved at 10% replacement. However, increasing WBCAP content reduced workability and density and slightly increased water absorption due to its porous structure and low specific gravity. These outcomes demonstrate that WBCAP’s pozzolanic activity contributes to strength improvement, while its physical characteristics influence fresh and durability-related properties. In conclusion, WBCAP can be effectively utilized in concrete at 7.5–10% replacement, offering mechanical benefits and supporting sustainable waste management. Future research should aim to enhance WBCAP reactivity through finer grinding and carbon reduction, and to investigate long-term durability and microstructural characteristics.</p>