Tensile performance, ultrasonic pulse velocity, and chloride ion content of roller-compacted concrete (RCC) incorporating single and dual nickel slag aggregate replacement

This study investigates the effects of single and dual nickel slag aggregate replacement on the tensile performance and chloride ion content of Roller-Compacted Concrete (RCC), supported by ultrasonic pulse velocity (UPV), digital image correlation (DIC), and material characterization of the nickel slag aggregates. Although nickel slag has been widely studied as an aggregate substitute in conventional concrete, its combined use as both fine and coarse aggregate in RCC remains insufficiently explored. The rapid growth of the nickel industry has generated large quantities of nickel slag, creating a need for sustainable utilisation strategies in concrete applications. Single replacement was carried out by substituting natural fine and coarse aggregates with nickel slag at levels of 0%, 25%, 50%, and 75%. Based on the gradation characteristics of the single-replacement mixtures, a fixed 50% coarse nickel slag content was combined with 25%, 50%, and 75% fine nickel slag content in the dual-replacement phase. The results show that moderate nickel slag incorporation increases splitting tensile strength and hardened density, with optimum performance generally obtained at 25–50% replacement in the single-replacement mixtures. Exponential regression indicated moderate-to-strong empirical correlations between UPV and splitting tensile strength with R²= 0.64–0.75. DIC analysis revealed stable and well-defined tensile strain localisation along the failure plane, particularly in cubic specimens. Chloride ion contents remained within acceptable limits for plain concrete applications. Overall, this study highlights the technical feasibility and performance benefits of employing nickel slag as both fine and coarse aggregate in RCC, offering a viable pathway for sustainable waste valorisation in infrastructure applications.