Insight into the durability of concrete based on ultrafine ground granulated blast furnace slag, phosphogypsum, and steel slag

The development of fully solid waste-based concrete offers a promising sustainable solution to reduce environmental impact and conserve natural resources. However, its durability under aggressive environmental conditions remains a major concern limiting wider application. This study systematically evaluates the durability performance of ultrafine solid waste-based concrete (UFBC) composed of ground granulated blast furnace slag, phosphogypsum, and steel slag, focusing on sulfate attack, carbonation, chloride penetration, and freeze-thaw resistance. Experimental results indicate that after 250 freeze-thaw cycles, UFBC maintains a relative dynamic modulus above 75% and mass loss below 5%, outperforming Portland cement-based concrete (PCBC) and unground solid waste-based concrete (UBC), which failed after 150 cycles. Sulfate corrosion in UFBC primarily produces needle-like ettringite (AFt), causing less microstructural damage than the gypsum crystals formed in PCBC and UBC. UFBC exhibits significantly lower electric flux values (around 770–860 C) and water absorption rates compared to PCBC and UBC, attributable to a dense pore structure and enhanced formation of aluminate hydration products, which effectively hinder chloride migration. Despite lower alkalinity, UFBC’s carbonation depth after 28 days (as low as 0.32 cm) closely matches that of PCBC and is substantially lower than UBC. These findings demonstrate that ultrafine grinding of solid wastes significantly enhances hydration and pore refinement, resulting in concrete with superior durability and environmental benefits. This work provides critical insights for the design of high-performance, sustainable concrete for service in aggressive environments.