Fractal dimension of steel slag foamed concrete and its connection with compressive strength

This study employed a physical foaming method to prepare foam concrete with steel slag (SS) partially replacing cement. The compressive strength was tested at different SS replacement ratios (0-50%). Through SEM testing, combined with ImageJ image analysis and the box-counting method, the fractal dimension was calculated. The results indicated that the pore size distribution of the steel slag foam concrete (SSFC) approximately followed a lognormal distribution. With increasing SS replacement ratio, both the average pore size and fractal dimension first decreased and then increased, reaching minimum values at a 20% SS replacement ratio, where the pore structure was the most uniform, with fewer large pores and the smallest fractal dimension D. In contrast, the compressive strength initially increased and then decreased with higher SS content, also peaking at the 20% replacement ratio. The observed trend of compressive strength decreasing with increasing fractal dimension D suggests that a lower D value corresponds to a more uniform pore distribution, with pores predominantly concentrated in relatively smaller size ranges, thereby reducing the formation of large pores that are prone to causing failure. Based on the fractal characteristics of the pores, a quantitative model was established to describe the relationship between compressive strength, fractal dimension, and porosity. This model clearly demonstrates a negative correlation between strength and fractal dimension, and it showed a good fit (R² > 0.99) when validated against experimental data. The research demonstrates that an appropriate amount of steel slag can effectively optimize the pore structure and enhance the mechanical properties of foam concrete, providing theoretical and engineering insights for the resource utilization of industrial solid waste.