Basalt fiber reinforcement of carbonation-cured soft soil stabilized with GGBS-steel slag-carbide slag binder: Strength, resistivity and microstructural characteristics

Carbonation curing provides a promising pathway for improving industrial-solid-waste-based stabilized soils, while basalt fiber reinforcement can further enhance their mechanical behavior. In this study, basalt fiber-reinforced soft soil stabilized with ground granulated blast-furnace slag, steel slag, and carbide slag was prepared. The effects of carbonation duration, fiber length, and fiber volume fraction on electrical resistivity, mechanical properties, carbonation depth, reaction products, fiber-soil/binder interface, and pore structure were systematically investigated. The results showed that carbonation curing and appropriate basalt fiber incorporation improved the measured resistivity and mechanical properties of the stabilized soil. The best overall strength performance was obtained at a fiber length of 6 mm and a fiber volume fraction of 1.8% under the present laboratory conditions. Under this condition, the compressive and flexural strengths after 4 d carbonation curing reached 1.4681 MPa and 0.7813 MPa, respectively, which were 142.7% and 121.2% higher than those of the corresponding ordinary-cured specimens with the same fiber parameters. Supplementary UCS tests on the selected mixture showed that the UCS reached 0.9741 MPa at 7 d under the OC3d + CC4d regime and 1.1449 MPa at 28 d under the OC3d + CC4d + OC21d regime, corresponding to increases of 85.63% and 80.64% over the ordinary-cured controls, respectively. Carbonation-depth results indicated that basalt fiber incorporation mainly affected early-stage carbonation penetration, while the tested section was almost fully carbonated after 4 d. XRD, FTIR, and TGA results indicated the formation of carbonate-related products, especially CaCO 3 . SEM-EDS and XPS revealed Ca-rich and Si-Al-containing deposits on soil-particle and extracted fiber surfaces, suggesting the development of a composite soil particle-product-fiber interface. MIP results showed that carbonation curing and fiber incorporation modified the pore structure through pore-size redistribution and matrix densification, whereas excessive fiber addition was associated with fiber clustering and increased coarse-pore contribution. Overall, a synergistic cementitious-carbonate-basalt fiber reinforcement mechanism is proposed, involving matrix densification, fiber bridging/crack restraint, and soil-product-fiber interfacial bonding.