Factors Influencing Chloride Diffusion in Recycled Aggregate Concrete: Based on Three-Dimensional Polyhedral Aggregate Model

Numerical Solution for Chloride Transport at the Corners of Square Piles Subjected to Wetting–Drying Cycles

The durability of marine concrete square piles is critically governed by chloride transport at the corners of piles, regions subject to multi-directional erosion and pronounced accumulation under cyclic wetting–drying conditions. In this study, we developed a two-dimensional coupled moisture–chloride convection–diffusion model for a quarter section of the corner of a square pile, incorporating the time-dependent surface chloride concentration and a nonlinear moisture diffusion coefficient. The governing equations were numerically solved using the unconditionally stable alternating direction implicit (ADI) finite-difference method, which effectively overcomes the instability issues inherent in long-term simulations of strongly coupled systems. Model predictions were validated against experimental data from the literature, showing good agreement. Parametric investigations revealed that (1) the effect of moisture–chloride coupling is significant, with a low initial degree of saturation intensifying capillary-driven convection and accelerating early-stage chloride ingress; (2) a higher water-to-cement ratio markedly increases pore connectivity, exacerbating chloride accumulation under bidirectional erosion; and (3) increasing the drying-to-wetting time ratio effectively reduces net chloride buildup by curtailing the total duration of immersion. These findings provide a theoretical foundation for durability design and service-life assessment regarding square pile foundations in marine tidal and splash zones.

Research on Multiscale Simulation Methods for Thermal Response of Cemented Sand–Gravel Dams

Cemented sand and gravel (CSG) dams have been widely applied due to their simple construction and use of local materials. With the increasing occurrence of extreme weather events, temperature has become an important factor affecting the safe operation of dams. To investigate the temperature stress response of CSG dams under low-temperature conditions and achieve cross-scale analysis, an adaptive macro–meso finite element method is proposed. Through an iterative “solution–evaluation–mesh adjustment” procedure, meso-scale modeling is performed in high-stress regions, and the results are compared with those obtained using the conventional submodeling method. The results show that, under low-temperature conditions, temperature gradients and thermal stresses are mainly concentrated near the dam surface, with limited influence on the interior, while hydraulic load remains the dominant controlling factor. The local stress distribution patterns obtained by the two methods are generally consistent, and both can reflect stress concentration near the aggregate–mortar interfaces. The proposed method can characterize local meso-scale responses within a global computational framework, providing a reference for cross-scale analysis of the temperature response and the identification of local unfavorable stress regions in CSG dams.

Numerical modelling of suction diffusion in unsaturated expansive soils under climatic fluctuations

The behaviour of expansive clay soils is highly influenced by climatic variations that govern the hydric exchanges between the atmosphere and the ground surface. These fluctuations cause changes in soil suction, leading to significant volumetric variations in expansive soils and resulting in differential settlements of lightweight structures, which can induce structural damage. Despite the critical role of these hydroclimatic processes, few models are able to describe the evolution of soil suction under realistic boundary conditions. In this study, a two-dimensional diffusion model is proposed to simulate the temporal and spatial evolution of suction beneath a structure, considered as impermeable, under the influence of climatic fluctuations and over selected time steps. The model is based on the numerical solution of the diffusion equation in unsaturated porous medium, formulated in terms of suction. The boundary conditions incorporate a surface water balance accounting for infiltration and evaporation, using meteorological data from the Météo-France SIM2 model. Hydraulic soil parameters, such as unsaturated permeability and water retention curve expressing suction as a function of water content, are defined from empirical relationships reported in the literature. The model is applied to a clay soil whose parameters are derived from the Chaingy experimental site (France) using daily climatic data for the year 2025. The simulations highlight a strong seasonal variability of suction concentrated within the upper soil layers, while the presence of an impermeable surface zone representing the structure significantly attenuates suction fluctuations beneath the foundation and induces marked horizontal gradients during dry periods.

Integrating macroscopic geometry and fluid-fracture feedback in dissolution analysis beyond isolated factors.

The acidic dissolution behavior of calcite is an important process associated with geological environments such as karst-related systems and carbonate weathering. The study investigates the fundamental coupling mechanisms among geometric characteristics, fluid transport, and dissolution kinetics through controlled numerical simulations. The core innovation lies in the systematic quantification of the independent impact of the macroscopic curvature (represented by the aspect ratio Rm) on dissolution kinetics by introducing the parameter "Curvature-Dissolution Rate Coupling Response Coefficient (RC)" for the first time, and in revealing the interplay between two-dimensional fracture structure and fluid dynamics. Two-dimensional geometric models of isolated calcite particles and fractured matrices were established coupled with a dynamic mesh approach. For elliptical particles, the dissolution rate initially decreases and then increases with increasing Rm, a trend consistent with the variation of the specific surface area analogy value (Bv). The variation of RC indicates that the reaction rate is highly sensitive to curvature changes when Rm < 1. Multiple nonlinear regression analysis (Sd = 0.037 Va0.763ac1.822Rm-0.283 (R2 = 0.972)) further reveals that among the acid injection rate (Va), acid concentration (ac), and aspect ratio (Rm), ac exerts the most dominant control on the shrinkage degree (Sd). At the fracture scale, acid etching drives the morphology toward channelization and significantly attenuates the nonlinear behavior of fluid flow, clarifying the dynamic feedback mechanism inherent in fluid-fracture interaction.

JOURNAL OF CIVIL ENGINEERING

Chloride diffusion investigation under different magnitudes of hydrostatic pressure for pre-cracked concrete

The service life of the reinforced concrete structure in the marine environment can be impaired significantly due to chloride-induced corrosion. However, how the chloride diffusion in pre-cracked concrete structures is affected by the hydrostatic pressure is poorly understood. This study experimentally examined the effect of hydrostatic pressure on the chloride diffusion in pre-cracked concrete. Cracks with five different widths, i.e., 20 μm, 40 μm, 60 μm, 80 μm, and 100 μm, were manually created each using a splitting tensile apparatus. The chloride diffusion in the concrete with a certain crack was then studied under four different hydrostatic pressures of 0 MPa, 0.1 MPa, 0.3 MPa, and 0.5 MPa. Experimental results show that the chloride diffusion in concrete with a crack greatly relies on both the hydrostatic pressure and the crack width. The chloride concentration increases as the hydrostatic pressure grows, particularly for the wider cracks with width ranging from 60 μm to 100 μm. Unexpectedly, the hydrostatic pressure has a negligible effect on the chloride distribution in the concrete with a crack width no larger than 40 μm. Thus, the critical crack width is between 40 and 60 μm. Both the chloride diffusion coefficient and the chloride concentration of concrete at a certain depth increased gradually as the hydrostatic pressure increased, the latter of which exhibited a linear relationship with the hydrostatic pressure The experimental findings enrich our understanding of the behavior of pre-cracked concrete when exposed to chloride-induced corrosion at different depths of marine environments.