Experimental and microstructural investigation on the strength and frost resistance of basalt fiber reinforced steel slag foamed concrete

Aiming to facilitate the high-value repurposing of industrial steel slag, this investigation synthesized basalt fiber-reinforced steel-slag foamed concrete (BFSFC) incorporating fiber volume fractions of 0%, 0.15%, 0.30%, and 0.45%. The experimental study assessed compressive and flexural capacities alongside resistance to freeze-thaw cycling, while micro-void was reconstructed via X-ray CT and corroborated by SEM imaging. Grey Relational Analysis (GRA) was subsequently utilized to correlate pore metrics with strength degradation under freezing conditions. Empirical findings identify 0.30% as the critical fiber volume fraction; this optimal mix yielded a 28-day compressive strength of 1.322 MPa (a 12.03% increment over the reference) and elevated flexural strength to 0.517 MPa (an increase of approximately 64%). Following 15 freeze-thaw iterations, the BFSFC2 specimen maintained a mass loss below 5% and restricted strength deterioration to 8.69%, a sharp contrast to the 31.14% decay observed in the control group. Microscopic analysis attributes this stability to a fiber-induced reduction in pore network complexity and morphological refinement. Furthermore, GRA confirms that fiber dosage exhibits the strongest correlation with fractal dimension (0.991), whereas frost-induced strength decline is primarily governed by fractal dimension (0.805) and large pore size (> 200 μm, 0.743), highlighting the dominance of pore network complexity and large pore-defects in freezing behavior. Conclusively, BFSFC2 provides a balanced improvement in mechanical performance and freeze-thaw resistance, supporting a microstructure-based optimization route for producing lightweight foamed concrete using steel slag for cold regions.