Revolutionizing Recycled Aggregate Concrete: A Dual Approach Using HCl Treatment and Silica Fume

Debris from building and demolition projects, as well as the shortage of natural resources, have become more pressing issues on a global scale in recent times. Even though concrete, the utmost adaptable building material, is a vital factor in the development of the infrastructural and industrial sectors, it has been claimed that it is not an environmentally friendly material due to its potential for profound environmental influence beyond its use and critical resource-consumption nature. Nevertheless, it will continue to be the dominant building material utilized globally. The present research aims to investigate the synergistic effects of the treatment of recycled concrete aggregate (RCA) by hydrochloric acid (HCl) and the replacement of cement by silica fume (SF) on the mechanical properties of produced concrete. Four groups of concrete mixes were prepared: (1) untreated recycled concrete aggregate (URCA), (2) HCl-treated recycled concrete aggregate (TRCA), (3) URCA with SF replacement, and (4) TRCA with SF replacement. The HCl treatment was applied at four molarities (0.2M, 0.4M, 0.6M, and 0.8M), while SF was used to replace cement by weight at four ratios (5%, 10%, 15%, and 20%). The results were evaluated in terms of the 7, 14, and 28-day compressive strength. The findings indicated that TRCA mixes significantly outperformed URCA mixes in terms of the mechanical properties, namely the 28-day compressive strength, in which the optimal mix was that with 100% TRCA by 0.4M HCl combined with 5% SF replacement. The results also demonstrated that 0.6M HCl treatment significantly enhanced the quality of RCA by removing weakly adhered mortar, leading to a nearly 21% rise in the 28-day compressive strength compared to URCA with complete replacement. Indeed, adding further SF enhanced the performance, as using 75% of TRCA+10% SF achieved the highest compressive strength of 38.7 MPa at 28 days, equalling around 25% improvement over the URCA with the same replacing level. Doi: 10.28991/CEJ-2025-011-05-08 Full Text: PDF