Effect of steel slag on the corrosion resistance of reinforced cement mortar

Steel slag is an industrial solid waste that causes serious environmental hazards when stockpiled without treatment. Existing research mainly addresses static corrosion of steel-slag concrete, whose conclusions cannot be directly extended to coastal zones, where dry–wet cycles modify degradation mechanisms through repeated salt dissolution-crystallisation. Moreover, systematic investigations into preferred mix proportions of water–binder ratio and steel slag content for chloride and sulfate dry–wet attack separately remain scarce. This work explores steel slag-reinforced cement mortar resistance under 5% sodium chloride (NaCl) and 5% sodium sulfate (Na2SO4) dry–wet cycles (water–binder ratio: 0.3–0.5 and steel slag content: 0–20 wt.% of binder). Under sodium chloride cycling, specimens with 10% steel slag and 0.4 water–binder ratio achieved optimum comprehensive performance at 20 cycles: mass loss rate, loss of relative dynamic modulus of elasticity, electrical resistance decrease rate and steel corrosion rate dropped by 73%, 82%, 76% and 47%, respectively. For sodium sulfate exposure, specimens with 15% steel slag and 0.4 water–binder ratio yielded the best performance. Multi-scale micro-characterisation (scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction) reveals that steel slag suppresses corrosion product generation. This study proposes favourable mix proportions for this material under the test conditions and offers experimental support for the utilisation of steel slag in coastal engineering.