Effect of replacement ratio of ferronickel slag aggregate on characteristics of cementitious mortars at different curing temperatures

Aggregates significantly affect the quality and durability of concrete, making them vital to the construction industry. Current research is focused on efficiently utilizing various industrial byproducts in the concrete industry to reduce environmental damage and achieve sustainable practices. In this study, we evaluated the mechanical properties of cementitious mortar using blast-furnace-slag powder (BSP) and a mixed aggregate of natural sand, ferronickel slag (FS), and blast-furnace slag (BS) at curing temperatures of 20 and 40 ℃. Microstructural investigations, including scanning electron microscopy (SEM) and energy-dispersive–X-ray spectroscopy (EDS), were performed to evaluate these materials. When cured at 20 °C, the 7-d compressive strength of the samples using only cement as a binder was approximately 16–26.5% higher than that of the control sample, comprising ordinary Portland cement and natural sand. However, the compressive strength of the samples using BSP partial cement replacement was relatively low compared to the control sample. When cured at 40 ℃, the compressive strength of all samples using steel-slag aggregates (including BS and FS fine aggregates) was higher than that of the control sample, regardless of the use of BSP partial cement replacement. In this study, the chloride ion penetrability resistance of the control sample was the lowest among all investigated systems, whereas the use of 40% BSP cement replacement and 50% FS fine aggregate yielded the highest chloride ion penetrability resistance at all curing temperatures. SEM-EDS analysis revealed a denser surface and the presence of numerous hydration products in the sample using slag aggregate compared with the control sample.