The escalating global production of waste tires exceeding 1.5 billion units annually presents an acute environmental challenge that demands integration with sustainable construction strategies. This study investigates the mechanical and physical performance of concrete incorporating heat-treated crumb rubber (CR) as a partial fine aggregate replacement at six substitution levels: 20%, 30%, 40%, 50%, 60%, and 70% by volume. A low-energy thermal pre-treatment protocol (100°C for 4 hours) was applied to modify CR surface morphology and enhance rubber-cement interfacial bonding without the use of hazardous chemical reagents. M25 grade concrete specimens (150 × 150 × 150 mm cubes) were prepared using the ACI 211.1 absolute volume method and evaluated for compressive strength at 7 and 28 days, fresh and hardened density, and workability (slump). The control mix achieved a 28-day compressive strength of 31.81 MPa and a hardened density of 2420 kg/m³. Compressive strength declined systematically with increasing CR content, reaching 5.57 MPa at 20% replacement (F20T) and 0.48 MPa at 70% replacement (F70T), representing reductions of 82.5% and 98.5%, respectively. Hardened density decreased from 2298 kg/m³ (F20T) to 1403 kg/m³ (F70T), corresponding to a maximum weight reduction of 42.0%. Workability decreased progressively, with slump values ranging from 156 mm (F20T) to 121 mm (F70T). The thermal treatment improved rubber surface conditions but was insufficient to restore structural-grade strength at high replacement levels. Nevertheless, heat-treated crumb rubber concrete (HTCRC) exhibits considerable potential for non-load-bearing, lightweight applications including partition walls, sound barriers, and insulation elements, offering substantial waste diversion and resource conservation benefits. This study extends the existing knowledge base previously largely confined to ≤30% replacement ratios by providing systematic performance data across a wider range (20–70%) under tropical climatic conditions relevant to developing nations.