Experimental Study on the Behavior of Reinforced Recycled Concrete Aggregate Beams under Direct Fire Flame

This study aims to analyze the structural behavior of reinforced concrete beams incorporating recycled concrete aggregate RCA subjected to direct fire flame. Evaluating the suitability of used in fire-prone structural environments. The experimental program was conducted using reinforced concrete specimens with standardized dimensions and reinforcement detailing. A constant concrete cover of 25 mm was maintained across all specimens to ensure uniform thermal exposure to the steel reinforced bars. The beams were divided into five primary groups based on two key parameters: the percentage of RCA and whether the beam was exposed to fire. Reference Group B0: Three beams made entirely with natural concrete aggregate NCA not exposed to fire, serving as the baseline for structural performance under ambient conditions. Group B1: Two beams with the same reference mix exposed to fire, intended to isolate the thermal effect from material substitution. Groups B2, B3, B4: Each group includes two fire-exposed beams with increasing recycled aggregate content—50%, 75%, and 100%, respectively designed to investigate the interaction between sustainability and thermal degradation, and to quantify the impact of aggregate replacement on fire resistance. The results revealed a marked reduction in peak load capacity and a significant increase in deflection due to fire exposure, even in beams made with ordinary concrete. As the recycled aggregate content increased, structural performance continued to decline, with peak load dropping from 41.375 kN at 0% RCA to 33.34 kN at 100%, indicating a progressive loss in flexural resistance under thermal stress. Maximum deflection values also varied, generally increasing with higher recycled content, suggesting a shift in failure mode and flexural behavior.