Ferronickel slag is the solid waste slag produced by smelting nickel-iron alloy. After grinding ferronickel slag into powder, it has potential chemical activity. It can partially replace cement and reduce the amount of cement, and is conducive to environmental protection. The mechanical properties of soil cement were investigated through the compressive strength test and inter-split tensile test of ferronickel slag powder soil cement with different dosages. To further study the mechanism of ferronickel slag powder's action on soil cement microscopically, the microstructure of soil cement was analyzed by using a scanning electron microscope and nuclear magnetic resonance equipment. The results of the study show that the incorporation of ferronickel slag powder can enhance the compressive and tensile strength of soil cement. The best performance enhancement of ferronickel slag powder was achieved when it was doped with 45% of its mass. The hydration products of soil cement increased with the increase in the doping amount, but the excessive doping of ferronickel slag powder would lead to a weakening of the hydration reaction and a decrease in the strength of the soil cement. At the same time, ferronickel slag powder plays the role of filling the void of soil cement. With the increase in ferronickel slag powder, the large pores inside the soil cement are reduced and the structure is denser.

Chemical stabilization is considered a more effective and efficient method for improving soft soil in road foundation construction. Nickel slag, a byproduct of the nickel industry, has the potential to be developed as an environmentally friendly pozzolanic material for soft soil improvement. Our previous research has shown that nickel slag enhances the mechanical properties of high-plasticity organic soil but fails to meet road foundation standards. As such, additional materials are needed to achieve the required specifications. This study aims to analyze the effect of adding aluminum hydroxide [Al(OH)3] to soil stabilized with nickel slag. The addition of Al(OH)3 is based on weight ratios of nickel slag at 1.5, 2.5, and 3.5. The effectiveness of adding nickel slag was assessed based on the unconfined compressive strength (qu) of the mixture matrix. In addition, mineral characterization of the mixture matrix was tested using X-ray diffraction (XRD) to observe changes in mineral fractions. The results of this study indicate that the addition of Al(OH)3 can improve the mechanical performance of soft clay soil better than soil stabilized with nickel slag alone, with the 1.5% weight ratio providing the highest compressive strength value of 237.39 kPa. This improvement may be due to the formation of pozzolanic reactions, including C-S-H, C-A-H, and C-S-A-H, as shown by the XRD test results.