Behavior of concrete with recycled concrete aggregate and admixtures of coconut fiber and rice husk ash at room temperature and under fire conditions

Abstract

Abstract The civil construction sector significantly impacts the environment, mainly through the generation of construction and demolition waste. Recycling and reusing such waste, particularly through the incorporation of recycled concrete aggregate (RCA), has become an effective strategy to mitigate those effects. This study investigates the mechanical behavior of concrete produced with RCA and sustainable admixtures of coconut fiber (CF) and rice husk ash (RHA) under both room temperature and fire exposure conditions. Seven concrete mixtures were prepared - a reference mix with no admixtures, three with CF (2.5%, 5%, and 10%), and three with RHA (5%, 10%, and 20%), all with a 30% replacement of natural coarse aggregate by RCA. The experimental program included consistency tests in the fresh state and compressive, splitting tensile, and dynamic modulus of elasticity tests at 14 and 28 days and after exposure to peak temperatures of 200°C, 400°C, and 600°C. The results indicated higher admixture contents reduced consistency, whereas RHA20 mix achieved the best overall mechanical performance, particularly after fire exposure. According to the findings, the incorporation of RHA and CF can improve sustainability and, when combined with further optimization of the mix design, particularly regarding the water-to-cement ratio, shows potential for the development of eco-efficient concretes for structural applications, including those subjected to elevated temperatures.