Effect of Polypropylene Fibres and Silica Fume on the Compressive Strength of Concrete Incorporating Recycled Aggregate

Abstract

This article evaluates the influence of polypropylene fibres (PPF) and silica fume (SF) on the mechanical properties of concrete with a design compressive strength of 210 kg/cm2 incorporating recycled coarse aggregate (RCA), as a sustainable alternative for reusing construction and demolition waste. The aggregates were characterised in accordance with ASTM standards, and the mix design was developed using the ACI 211.1 method. Nine concrete mixtures were prepared following a Taguchi L9 orthogonal array, combining three levels of RCA (20%, 50%, and 100%), PPF (0.3%, 0.5%, and 0.7%), and SF (5%, 7%, and 9%). The workability of the nine mixtures was evaluated through slump tests, and the compressive strength at 28 days was determined using 36 cylindrical specimens. The results indicate that the slump values ranged from 3.1 to 3.8 inches, slightly below the theoretical target slump of 4 inches. Furthermore, all mixtures exceeded the design compressive strength, with values between 225.95 and 295.08 kg/cm2, corresponding to increases of 7.6% to 40.5% relative to the target strength of 210 kg/cm2. In addition, the optimal mixture was identified as consisting of 50% RCA, 0.7% PPF, and 9% SF. In conclusion, the combined incorporation of RCA, PPF, and SF enables the production of concrete with a design strength of f′c = 210 kg/cm2, exhibiting controlled workability and mechanical performance superior to that of conventional concrete.