Natural and synthetic fiber reinforced recycled aggregate concrete subjected to standard fire temperature.

The increasing scarcity of natural materials and rising construction costs have prompted the need for alternative materials that can match the performance of conventional aggregates. This study explores the use of recycled aggregate concrete (RAC) as a sustainable alternative, supplemented with natural and synthetic fibers to overcome the inherent strength limitations caused by the residual cement paste on the aggregate surface. To enhance the mechanical and thermal stability of RAC, steel, polypropylene, and coconut fibers were incorporated. The rheological, hardened, and post-fire properties of fiber-reinforced RAC were thoroughly investigated. After 28 days, the porosity of RAC with fiber reinforcement was observed to be less than 2 %. The concrete was also exposed to elevated temperatures as per ISO 834 guidelines to assess its thermal performance. Key parameters such as mass loss, crack width, porosity, and strength degradation were analyzed. Image analysis was used to track surface modifications and measure surface porosity after heating. Among the fiber types, steel fiber reinforced concrete exhibited superior mechanical and thermal performance, followed by coconut fiber reinforced concrete, making coconut fibers a viable natural alternative to synthetic fibers. RAC without fibers displayed the highest porosity (20 % and 32 %) after exposure to 821 °C and 1029 °C, respectively. Strength degradation ranged from 40 to 50 % after heating to 821 °C, increasing to 74-80 % at 1029 °C, irrespective of fiber type. This research highlights the potential of fiber-reinforced RAC for structural applications, offering a sustainable solution with comparable strength and durability to conventional concrete.