Investigation of the multi-factor influence on the saturation of steel slag surface pores under pressure conditions

Steel slag, as a principal solid waste in the steel industry, exhibits high mechanical strength and wear resistance. However, its extensive surface open porosity significantly compromises durability, thereby limiting its resource utilization. This study employs an air pressure-driven technique to enhance gas-liquid displacement efficiency within the open pores of steel slag, achieving effective internal pore filling.The grouting saturation index was introduced and combined with microscopic testing to quantitatively evaluate the effects of air pressure, grout viscosity, and temperature on filling efficiency. Experimental results demonstrated that the negative-pressure filling method was safer and more efficient, increasing grouting saturation by approximately 20% compared to positive-pressure filling. When using low water-cement ratio (0.8–1.0) cement paste, its higher viscosity and poorer fluidity led to a 3.5-fold improvement in grouting saturation compared to a water-cement ratio of 2.0. However, elevated temperatures (from 25°C to 50°C) accelerated cement hydration and agglomeration, reducing grouting saturation from 22.45% to 14.05% and thus decreasing filling efficiency. Analyses via laser confocal microscopy, SEM, and XRD revealed that a dense coating formed on the steel slag surface, fundamentally improving the macroscopic morphology the arithmetic mean roughness (Sa) and the mean height of irregularities (Sz) reduced by 59.8% and 37.8%, respectively, while microscopically reducing irregular open pores, passivating their entrances, and simplifying the phase composition, thereby demonstrating surface densification and homogenization.