Deterioration Mechanism and Constitutive Model of BFRC Corroded by Acid Rain

Corrosion behaviour of Q235 steel in accelerated simulated acid rain condition

Fracture evolution of micritic bioclastic limestone under Brazilian splitting: a comparison between natural and water-saturated states

The tensile strength properties and the initiation and propagation of tensile cracks within micritic bioclastic limestone–which forms the surrounding rock mass at the tunnel exit of the Altash Water Conservancy Project–pose a threat to engineering stability. To investigate the differences in tensile strength and stress-induced crack evolution under natural and water-saturated conditions, a comparative experimental study was conducted using Brazilian splitting tests coupled with acoustic emission (AE) monitoring. The results demonstrate that, compared with natural specimens, saturated limestone exhibits a 16.54% reduction in tensile strength. The failure process can be categorized into three distinct stages: compaction, quasi-linear elasticity, and unstable crack propagation. Furthermore, AE analysis indicates that while overall AE activity decreases following water saturation, the proportion of tensile cracks increases from 92.30% to 95.14%. Conversely, under natural conditions, shear cracks are more active and initiate earlier. Microscopically, the high content of bioclasts and associated complex interconnected pores (e.g., body cavity and secondary dissolution pores) endow the rock with remarkable hydrophilic and water-retention characteristics. Coupled with the presence of the abundant hydrophilic mineral illite, these factors collectively exacerbate water-rock interactions, driving the significant degradation of the rock’s mechanical properties from both material and structural perspectives.

Mechanical degradation of limestone under thermo-chemical–mechanical coupling

A Porosity-Dependent Constitutive Model for Concrete Under Wetting–Drying Cycles: Experimental and Field Validation

The degradation of concrete under wetting–drying cycles significantly compromises the safety and durability of bridge structures; however, existing constitutive models often exhibit limitations in practical engineering applicability. To improve the engineering applicability of existing constitutive models, this study proposes a porosity-dependent uniaxial compressive constitutive model for concrete located in the wetting–drying zones of in-service bridge piers. This model is theoretically grounded in the strain equivalence principle and the Weibull statistical distribution. To validate the theoretical framework, six groups of concrete specimens with varying target porosities (15%, 20%, and 25%) were subjected to 15 consecutive 30-day sulfate wetting–drying exposure intervals, corresponding to a total exposure duration of 450 days. The macroscopic evolutions of porosity, mass variation, permeability coefficients, and uniaxial compressive stress–strain behavior were systematically evaluated. Furthermore, an independent field validation was conducted utilizing core samples extracted from the Saiqi Bridge, an in-service structure exposed to natural water-level fluctuations over a 25-year service period. The experimental results indicate that the theoretical stress–strain relationships predicted by the proposed model are in good agreement with the empirical measurements. In the field application, the core data revealed a reduction in concrete compressive strength from the initial design value of 40 MPa to 38.2 MPa. The porosity inversely predicted by the proposed model (16.9%) showed good agreement with the actual measured porosity (17%) of the bridge piers. By explicitly incorporating pore characteristics, the proposed model characterizes the mechanical deterioration of concrete. Consequently, it provides theoretical support for the performance assessment, numerical simulation, and structural strengthening of in-service bridges exposed to repeated wetting–drying exposure.

Durability Degradation and Fractal Strength Prediction of Bentonite-Slurry/Steel-Slag Foamed Concrete Under Corrosive Wetting–Drying Exposure

Bentonite slurry (BS) and steel slag powder (SS) were co-utilized to develop bentonite-slurry/steel-slag foamed concrete (BS-SSFC). The evolution of compressive strength and the associated deterioration mechanisms were examined after repeated wetting–drying exposure in four environments, namely H2O, H2SO4, NaOH, and Na2SO4, by combining mechanical testing with microstructural observations. The mix-design results indicate that, for the SS-only mixtures, 20% SS replacement produced a relatively high strength, whereas the binary SS-BS system reached its maximum strength at 10% SS and 5% BS; this combination was consequently adopted for the durability experiments. After 20 cycles, the severity of degradation followed Na2SO4 > H2SO4 > NaOH > H2O. XRD and SEM-EDS evidence shows that sulfate ions in the H2SO4 and Na2SO4 solutions favored ettringite-type expansive products, and Na2SO4 further caused salt-crystallization pressure during drying. For NaOH exposure, the main damage was related to reduced stability of cementitious phases together with ion redistribution and localized re-precipitation in a strongly alkaline pore environment. Based on fractal theory, an empirical strength–degradation correlation model was established by using SEM-derived two-dimensional apparent areal porosity as a structural parameter and by linking fractal dimension with the number of cycles. Within the scope of the present experiments, the model captures the empirical link between strength loss and apparent pore-structure deterioration in BS-SSFC; however, its use remains dependent on the image-acquisition procedure, thresholding method, and material system considered. The results provide useful support for using BS-SSFC in aggressive engineering settings such as saline ground and acid-rain regions.

Investigating the Effect of Secondary Phase Precipitation on Pitting Corrosion Behaviour of 26.54% Cr Super Duplex Stainless Steel