Micro-macro mechanical properties of fully weathered mudstone improved by steel slag

The softening properties of fully weathered mudstone (FWM) result in a precipitous decline in the mechanical strength of both the rock and soil, thereby posing a significant risk of severe engineering failures, including roadbed subsidence and slope instability. This study employs a range of analytical techniques, including unconfined compressive strength (UCS) tests, tensile strength tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and particles/pores and cracks analysis system (PCAS), to thoroughly investigate the enhancement of the mechanical properties of FWM by steel slag, sodium carbonate, and sodium hydroxide. The results demonstrate that an optimal dosage of steel slag in conjunction with sodium carbonate or sodium hydroxide, can effectively activate the steel slag and promote the generation of calcium silicate hydrate (C-S-H) and calcium aluminum silicate hydrate (C-A-S-H) gels, thereby efficiently filling the pores among mudstone grains. The modified mudstone exhibits reduced porosity and probability entropy, alongside an increased fractal dimension, resulting in enhanced compressive and tensile strengths. The gray correlation analysis shows a strong relationship between microscopic features and macroscopic mechanical behavior, where the impact of the fractal dimension is notably more significant. The findings suggest that combining steel slag with sodium carbonate or sodium hydroxide in a synergistic manner is an effective strategy to improve the mechanical properties of FWM. The objective of this research is to provide a solid scientific foundation and technical guidance for the enhancement and utilization of FWM in road engineering applications.