Compressive Strength and Its Calculation Method of Foam Concrete made of Steel Slag Sand

To achieve green environmental protection and solid waste recycling, and promote the efficient recovery and application of industrial solid waste such as steel slag in building materials, steel slag sand was used to partially replace cement in the preparation of steel slag foam concrete (SSFC). Compression tests were conducted on SSFC with different steel slag replacement ratios (SSR). The experimental results indicate that the compressive strength of SSFC initially increases and then decreases with the rise in SSR. Taking a dry density of 800 kg/m³ as an example, when SSR increases to 20%, the compressive strength reaches its peak value of 2.93 MPa. Further increasing the SSR leads to a decline in compressive strength.According to SEM results, as SSR increases, the large pores within SSFC are gradually filled, and the pore structure becomes more uniform and stable. At 20% SSR, SSFC exhibits the most homogeneous and compact state, corresponding to the maximum compressive strength. EDS analysis further reveals that an appropriate amount of steel slag promotes the formation of hydration products. C−S−H gels and other hydration products adequately fill the gaps between particles, with representative elements (Si, O) showing more pronounced enrichment and relatively uniform distribution. This contributes to the enhanced compressive strength of SSFC at an optimal SSR.However, when SSR becomes excessive, the fluidity of the paste is adversely affected, leading to the sedimentation and aggregation of steel slag. This results in structural inhomogeneity, damage to the pore structure, and a noticeable increase in large pores. Moreover, excessive steel slag impedes the formation of hydration products. EDS results also indicate a reduction in hydration products and a decreased distribution density of Si and O elements.Based on fractal theory, a relationship between porosity and compressive strength of SSFC was established. The predicted values calculated from this model show good agreement with experimental data, providing a reliable theoretical tool for predicting the mechanical properties and facilitating the material design of steel slag foam concrete.