Abstract
Excessive consumption of natural aggregates in concrete production has led to resource depletion and environmental degradation. Recycled aggregate concrete (RAC) offers a sustainable alternative; however, its mechanical strength and durability are often inferior, especially under aggressive acidic environments such as acid rain. This study aims to enhance the mechanical and durability performance of RAC by combining magnetized water (MW) and nano-silica (NS) as complementary modification techniques. A total of 80 concrete mixtures were prepared with varying recycled concrete aggregate (RCA) contents (0–100%), NS dosages (0–6%), and MW exposure times (0–30 min). The specimens were exposed to simulated acid rain with pH values of 2.5, 4.0, 5.5, and 7.0 for 28, 56, and 90 days. Tests for compressive strength, electrical resistivity, mass loss, and sorptivity coefficient were conducted to evaluate performance. Results showed that the use of RCA reduced compressive strength by up to 25.4%, while increasing the acidity from pH 7 to 2.5 caused an additional 16.2–25.4% decline. However, the synergistic use of 6% NS and 30-min MW improved compressive strength by up to 14.1% compared to control specimens. Similarly, the combination of MW and NS enhanced electrical resistivity by 12–38% and reduced mass loss and compressive strength by 33% and 32%, respectively, demonstrating a denser and more durable microstructure. These findings confirm that MW and NS mitigate the detrimental effects of acid exposure and recycled aggregates by accelerating cement hydration, refining pore structure, and strengthening the interfacial transition zone. The optimal mix was found at 25% RCA, 6% NS, and 30 min MW exposure, which achieved superior performance across all parameters. It is concluded that the combined application of MW and NS offers a feasible and eco-efficient approach to improve the corrosion resistance and sustainability of RAC under acid rain. Future studies are recommended to investigate the long-term field performance of RAC in other aggressive media such as chloride environments. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-38607-3.