Effects of steel slag aggregate and polycarboxylate superplasticizer on shotcrete

To address the depletion of natural sand resources and the environmental problems caused by steel slag accumulation, this study investigated the synergistic effects of steel slag fine aggregate and polycarboxylate superplasticizer on the performance of shotcrete. Laboratory tests systematically analyzed the effects of different steel slag replacement ratios (0%–50%) and superplasticizer dosages (1.4%–1.8%) on the slump and compressive strength of concrete, and further revealed the interaction between these two factors as well as the distinct strengthening mechanisms of fine and coarse steel slag. The results showed that increasing the steel slag content required a corresponding increase in superplasticizer dosage to achieve optimal engineering performance. Fine steel slag, with more exposed reactive phases, generated additional hydration products through hydration reactions, thereby enhancing the compactness and strength of concrete. In contrast, coarse steel slag mainly relied on its rough surface to enhance mechanical interlocking at the aggregate–cement interface, resulting in relatively limited strength improvement. On-site shotcrete tests on the recommended mix proportion (40% steel slag replacement and 1.6% superplasticizer dosage) demonstrated a slump of 133 mm, a rebound rate of 6.28%, and a 28-day compressive strength of 31.73 MPa. This study provides theoretical support and practical guidance for the efficient utilization of steel slag in shotcrete applications.