Slump monitoring and electrical resistivity comparison in concrete modified with steel slag as fine aggregate replacement

This study aims to investigate the effect of waste steel slag (SS) as partially replaced with cement and fine aggregate on concrete for different mixes in terms of compressive strength (CS) and electrical resistivity (ER). SS is a molten mixture of silicates and oxides that solidifies upon cooling, a byproduct of the steel-making process. Before conducting the design experiments, the optimal percentage of SS in both powder and fine aggregate forms was established through seven different mixes. This aimed to examine the influence of various SS particle sizes on CS. Based on the results achieved, the optimum percentage and effective size of SS were selected to modify and investigate the effect of SS on three different mixes of conventional concrete (M25, M35, and M47) in terms of CS, ER, and concrete slump. The resistivity of each mixture was assessed by implementing four-probe (4P) and two-probe (2P) techniques, ranging from the initial stages of curing up until the 28 days of the curing. The exclusion of the wire probe in the 4P technique is evidenced by the findings, which indicate that 4P is superior to 2P in terms of ER detection accuracy. Computing the correlation between the 2P and 4P approaches is crucial to obtain the correct resistivity value. The concrete slump value and initial resistivity (ρ_o) correlation model was developed. The results demonstrated that the concrete slump could be determined based on concrete with high accuracy, with the coefficient of determination (R²) 0.8 and 0.84 for 2P and 4P, respectively. Moreover, the findings also indicated that the CS of M25 concrete, when enhanced with SS, was 2.27% lower than that of M25 concrete without SS after 28 days of curing. In contrast, the CS of M35 concrete with SS modification was 6.74% higher than that of the unmodified M35 concrete. Similarly, for M47 concrete modified with SS, its CS was 12.8% greater than the original M47 concrete.