Strength improvement of M20 concrete using acid treated recycled coarse aggregate with fly ash

Abstract

Concrete, recognized for its strength and durability, poses significant environmental challenges due to natural aggregate depletion and emissions from cement production. This study investigates the potential of Recycled Coarse Aggregate (RCA) as a sustainable alternative to Natural Coarse Aggregate (NCA) and examines the synergistic effects of hydrochloric acid (HCl) treatment and fly ash incorporation on the performance of M20 grade concrete. Findings reveal that RCA can effectively replace NCA without compromising mechanical properties; however, acid treatment enhances RCA's bond with the cement matrix, leading to improved strength and durability. Furthermore, optimal mixes achieve a 25,7 % reduction in cement content when incorporating HCl with 25 % fly ash, alongside minor reductions in coarse and fine aggregates. Experimental results show that NCA achieves the highest compressive strength of 30,7 MPa, while untreated RCA shows a strength of 25,4 MPa. With HCl treatment, RCA reaches 30,0 MPa, and the optimal mix of 1,25 M HCl and 25 % fly ash yields the best performance at 32,6 MPa due to enhanced pozzolanic effects. This research emphasizes the importance of optimizing concrete mix designs through innovative treatments and sustainable materials, contributing to environmentally friendly construction practices.