The combined action of sulfate and chlorine salts erodes concrete structures in coastal and saline-alkali zones. The induced fractures under load also accelerate the deterioration of concrete. In this study, ion erosion tests of fractured coal-gasified ash slag (FC-GAS) concrete under dry-wet cyclic conditions were performed using ordinary concrete as the reference. The mass loss rates, the relative dynamic moduli of elasticity, and the distribution patterns of chlorine and sulfate ions of specimens in erosive environments of single sulfate salt, single chlorine salt, and mixed sulfate and chlorine salts were measured. The deterioration mechanism of FC-GAS concrete under coupled erosion by sulfate and chlorine salts was explored with SEM and XRD techniques. By introducing the influence coefficient and deterioration coefficient of the fracture width of FC-GAS concrete, a modified model describing the diffusion behavior of chlorine ions in FC-GAS concrete was established. The results show that for the concrete specimens after erosion in sulfate salt and the mixture of sulfate and chlorine salts, the mass and the relative dynamic modulus of elasticity first increased and then dropped. The deterioration of the concrete performance after soaking in the mixed solution was significantly lower than that of the specimen after dry-wet cycles in the single solution. The formation of fractures accelerated ion erosion. Chlorine and sulfate ions in the mixed solution could inhibit the diffusion of other ions. The diffraction peak strengths of the erosion products of the specimen after dry-wet cycles in the mixed solution were significantly reduced. The results calculated by the proposed modified model on the diffusion of chlorine ions in FC-GAS concrete agreed with the experimental results.

This study evaluates the effects of steel slag powder (SSP), fly ash (FA), and steel slag sand (SSS) on mortar compressive strength. A response surface methodology (RSM) based on central composite design (CCD) was employed to model 7-day, 28-day, and 91-day strength development, considering three quantitative variables: SSP, FA, and SSS. Statistical results confirmed the reduced cubic models were significant and predictive (R² > 0.97), with non-significant lack of fit and adequate precision. Experimental results revealed that SSP and FA negatively affected early-age strength due to dilution effects and low initial reactivity, whereas SSS slightly improved it by enhancing particle packing. At later ages, SSP exhibited nonlinear effects, where moderate dosages enhanced strength, while excessive replacement led to strength reduction. SSS showed a continuously positive contribution across all ages, particularly at 91 days. Perturbation plots, contour maps, and gradient analyses indicated that SSS played a dominant role at later stages and that maintaining a proper balance among supplementary cementitious materials (SCMs) and aggregate replacements is crucial. The developed models and response surfaces provide practical guidance for designing slag-based mortars with improved mechanical properties and enhanced sustainability.

Bond performance served as a crucial foundation for the collaboration between concrete and steel rebar. This study investigated the bond performance between coal gasification slag (CGS) concrete, an environmentally friendly construction material, and steel rebar. The effects of fine aggregate type, steel rebar diameter, and anchorage length on bond performance were examined through bond-slip tests conducted on 16 groups of reinforced concrete specimens with different parameters. By utilizing experimental data, a formula for the bond strength between steel rebar and CGS concrete was derived. Additionally, the BPE bond-slip constitutive model was modified by introducing a correction factor (k) to account for relative protective layer thickness. Findings indicated that substituting 25% of manufactured sand with coal gasification slag did not cause significant adverse effects on concrete strength or bond stress between concrete and steel rebar. The effect of steel rebar diameter on the ultimate bond stress was not obvious, whereas when the steel rebar diameter was fixed; the increase in anchorage length led to uneven distribution of bond stress and eventually reduced the ultimate bond stress. The modified bond-slip constitutive model agreed well with the experimental values and was able to more accurately reflect the bond-slip performance between CGS concrete and steel rebar. This study provided a theoretical basis for the conversion of CGS into a resource and for the application of CGS concrete.