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.