<![CDATA[Indonesia, located in a seismic-prone region, requires innovative concrete materials with high ductility and deformability, especially for critical elements such as beam–column joints. Crumb rubber concrete (CRC), produced by partially substituting fine aggregate with crumb rubber from recycled waste tires, offers this potential while supporting sustainable construction practices. This study aims to evaluate the effect of aqua-thermal treatment (washing and heating at 150°C for 1 hour) on the mechanical properties of CRC, including compressive strength, splitting tensile strength, elastic modulus, and Poisson’s ratio. The research method involved experimental testing on CRC cylindrical specimens with crumb rubber substitutions of 5% and 10% after 28 days of curing. Results show that CRC-5 achieved an average compressive strength of 34.25 MPa and splitting tensile strength of 2.74 MPa, higher than CRC-10. The elastic modulus of CRC-5 was 11,407.67 MPa, increasing to 12,843.33 MPa in CRC-10, although still lower than that of conventional concrete. Poisson’s ratio was recorded at 0.171 (CRC-5) and 0.230 (CRC-10), indicating greater deformability. Overall, CRC with moderate substitution (≈5%) and aqua-thermal treatment meets the structural concrete standard per SNI 2847:2019 and is considered effective for beam–column joints requiring good ductility. Further research is needed to optimize the balance between strength, stiffness, and ductility, for example through fiber reinforcement or additive materials.]]>
