<![CDATA[Concrete is one of the most widely used construction materials in infrastructure development, yet the extensive use of Portland cement contributes substantially to carbon dioxide emissions from cement production. This study investigates grouting cement and wood charcoal as partial cement substitutes in K-300 concrete to reduce conventional cement consumption while utilizing wood-derived waste. An experimental study was conducted at the Material Mechanics Laboratory, Faculty of Engineering, Universitas Islam Sultan Agung, using substitution levels of 0%, 5% (2.5% grouting cement and 2.5% wood charcoal), and 10% (7.5% grouting cement and 2.5% wood charcoal). Cylindrical specimens measuring 150 × 300 mm were used for compressive and splitting tensile tests, while 600 × 150 × 150 mm beams were used for flexural testing at 7 and 28 days. The results showed that the 5% substitution provided the best mechanical performance at 28 days, achieving an average compressive strength of 19.398 MPa, an 18.26% increase over normal concrete, splitting tensile strength of 2.900 MPa, a 45.73% increase, and flexural strength of 3.029 MPa, a 3.73% increase. The 10% substitution reduced mechanical performance, indicating that excessive carbonaceous material may hinder effective cementitious matrix development. The findings identify 5% substitution as the most favorable composition under the investigated conditions. The results provide an empirical basis for optimizing alternative cementitious materials while maintaining acceptable fresh-concrete workability and mechanical performance. ]]>
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