Investigation on the mechanical properties, durability of steel slag-silica fume composite coral concrete — engineering application exploration in offshore wind turbine foundations

IntroductionThe construction of offshore wind turbine foundations in the South China Sea faces exorbitant material transportation costs. While locally sourced coral aggregate concrete (CAC) offers an effective in-situ solution, the high water absorption of coral aggregates negatively impacts mechanical properties and durability. This study aims to develop a high-performance steel slag–silica fume composite coral concrete (SSCAC) to overcome these limitations.MethodsA systematic investigation was conducted using an L9(3³) orthogonal experimental design. The effects of water-to-binder ratio (w/b: 0.25, 0.30, 0.35), silica fume content (2%, 5%, 8%), and steel slag content (2%, 5%, 8%) on workability (slump), mechanical properties (compressive and splitting tensile strength), and rapid chloride permeability were evaluated. Microstructural evolution was characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM).ResultsRange analysis identified w/b as the dominant factor governing compressive strength, while silica fume content critically controlled workability and impermeability. The optimal mix proportion (S4: 5% silica fume, w/b 0.25, 5% steel slag) achieved a synergistic balance, exhibiting a high splitting tensile strength of 3.20 MPa and low chloride permeability (1842.3 C) without compromising construction applicability. SEM observations confirmed that SSCAC-4 possessed the smallest pore size and the tightest paste–aggregate interfacial bonding among all groups.DiscussionThe performance enhancement is attributed to a synergistic mechanism of "physical filling + chemical chloride binding + interfacial optimization." Silica fume underwent secondary hydration to form low Ca/Si ratio C–S–H gels, effectively refining pores and eliminating visible defects in the interfacial transition zone (ITZ). This research provides a theoretical basis and engineering guidance for the resource utilization of solid wastes and the durable, in-situ application of CAC in severe marine environments.