Concrete remains the most widely used construction material for buildings and infrastructure because of its high compressive strength, durability, and cost-effectiveness. However, fire exposure can significantly impair its structural performance through moisture loss, thermal cracking, spalling, and the degradation of cement hydration products. Although the fire behavior of normal- and high-strength concrete has been extensively studied, experimental evidence on low-strength concrete (f’c ≈ 10–15 MPa), which is still common in older buildings and public facilities in Indonesia, remains limited. This study investigates the effects of elevated temperatures on the residual compressive strength and visible deterioration of low-strength concrete with a target compressive strength of 12.5 MPa. A narrative literature review was combined with controlled laboratory experiments using cylindrical specimens exposed to temperatures of 200°C, 300°C, 400°C, and 500°C. Residual compressive strength was determined through standard compression testing, while surface deterioration was assessed by visual inspection. The results showed progressive strength reductions of 4.8%, 13.6%, 28.0%, and 42.4%, respectively, with one-way ANOVA confirming a significant effect of temperature on residual compressive strength (F (4,10) = 1015.07, p < 0.001). More severe deterioration was observed above 300°C, characterized by color changes, crack propagation, and friable concrete surfaces. These findings provide practical experimental evidence to support post-fire structural assessment and decision-making for the repair, strengthening, or demolition of low-strength concrete structures in Indonesia.
