This study has investigated the synergistic effects of corrosion and fatigue on lightly reinforced concrete (RCC) structures, with a focus on understanding the coupled deterioration mechanisms in real-world conditions. Concrete beams have been subjected to constant amplitude fatigue loading while submerged in a saline solution to simulate accelerated corrosion. The corrosion kinetics parameters, including corrosion current density (icorr), half-cell potential, and concrete resistivity, have been continuously monitored using a linear polarization resistance (LPR) device during fatigue loading. The study has employed a novel two-beam setup to compare the fatigue life and corrosion rate under coupled loading and staggered loading conditions. The results have demonstrated a significant increase in corrosion current density under fatigue loading compared to control specimens subjected to corrosion alone, highlighting the accelerated degradation due to the combined effects of corrosion and cyclic loading. Pitting corrosion has been found to dominate at the intersection of cracks and the reinforcement bars, with corrosion pits acting as fatigue crack nucleation sites. The study has revealed a clear correlation between corrosion progression and fatigue life, with the coupled corrosion and fatigue loading causing more severe damage and reducing the fatigue life of RCC beams compared to staggered loading conditions. This research has provided critical insights into the coupled corrosion fatigue mechanisms in lightly reinforced concrete flexural members, offering valuable information for understanding the long-term durability and safety of RCC structures subjected to both environmental and loading conditions. The findings have also contributed to the development of better predictive models for the performance and lifespan of concrete infrastructure exposed to aggressive environments.

External sulfate attack (ESA) is a leading cause of durability deterioration in concrete structures, primarily driven by expansion due to crystallization pressures associated with ettringite formation. This research develops a novel chemo-mechanical model to simulate degradation in cementitious materials under ESA conditions. The model integrates a pore-scale representation of the C-S-H gel, considering both reactive transport and poromechanical effects. Chemically, the model incorporates precipitation/dissolution kinetics and ionic adsorption/desorption at the C-S-H phase within a comprehensive reactive transport framework. Mechanically, a poromechanical model is coupled to the transport processes to capture local strain effects at the C-S-H gel scale. Three primary mechanisms contribute to the mechanical response: (i) the chemical reaction between monosulfate within the C-S-H phase and incoming sulfate ions, resulting in the eventual consumption of monosulfates, (ii) sulfate adsorption and subsequent desorption from the C-S-H surface, resulting in ettringite precipitation, and (iii) crystallization pressure exerted within the gel's interstitial porosity, driven by the equilibrium of sulfate ions in solution. The fully coupled chemo-mechanical model provides robust predictions of sulfate ion transport, capturing both the spatial and temporal evolution of sulfate adsorption in the C-S-H phase, while identifying zones with high sulfate concentrations. Additionally, the model reveals the influence of material parameters on chemo-mechanical interactions, offering valuable insights into their role in controlling mechanical expansion. The results show an encouraging correlation between predicted and experimental macroscopic strain values, validating the model's ability to simulate sulfate-induced degradation mechanisms in cementitious systems.

Concrete structures are widely used due to their long-term durability and strength; however, they are susceptible to deterioration and fracture once subjected to chemical reactions and/or mechanical stresses. One specific example of this type of degradation is the phenomenon of delayed ettringite formation that can occur under combined environmental conditions and exposure to high temperatures at early age. This often leads to the swelling, micro and macro-cracking and at a later stage the deterioration of massive concrete structures with loss of strength. In this context, the aim of the work is to predict, characterize and monitor the chemical and mechanical behavior of mature concrete affected by DEF pathology at “aggregate scale” using 3D numerical simulations. A composite parallelepiped sample composed of CEM I cement paste bonded to siliceous aggregate have been simulated to perform a qualitative comparison with experimental results (1×1×3 cm³ sample dimensions). The chemo-poromechanical model is based on the coupling between a poromechanical model, in the framework of Frictional Cohesive Zone Model for fracture. The initial chemical parameters and mechanical properties of the cement paste have been estimated from the chemical composition of the cementitious mix that was used in the previous experimental work. The effect of the initial degradation at the interface between cement paste and the aggregate have been studied. Our work shows that the initial cracks affect the ettringite precipitation and hence modify the cracking pathology in the sample. These results show good agreement with the crack propagation and swelling evolution in the sample as compared to experimental data.

This paper investigates the gas transport behaviors of a special type of concrete—shielding concrete—designed for use in nuclear structures, where mitigating radiation and ensuring long-term durability in harsh environments are critical.
Cracking is identified as a key factor influencing gas transport in nuclear environments, where it plays a critical role in determining material performance. In the current phase of the research, cracks and gaps, caused by significant variations in the interfacial transition zone (ITZ) and influenced by thermal treatment of concrete, depending on the type of aggregate and cement, were analyzed. Three types of concrete mixtures incorporating magnetite, serpentinite, and a combination of both aggregates are studied, alongside two types of cement: CEM I and CEM III. The transport properties of these concrete mixes, crucial for assessing their performance in nuclear shielding applications, were evaluated using three complementary methods: the Cembureau method for gas permeability, the Torrent method for measuring surface permeability, and the Air Permeability Index (API) using the Autoclam method. Additionally, microstructural analysis was conducted using scanning electron microscopy (SEM) to gain deeper insights into the material's behavior.
The impact of microcracks on permeability was examined, as such cracks often behave differently under gas transport conditions. In the next phase of the research, supplementary cracking will be intentionally induced—both mechanically and thermally—to simulate the conditions expected in typical nuclear operations.

This study introduces a novel poromechanical approach to analyse fire-induced fractures and transport phenomena, such as spalling, crack propagation, and vapour pressure, by accounting for gaseous kinetics. A key feature of this framework is that, across all temperature ranges, vapour diffusion and the bulk movement of vapour and liquid water maintain thermodynamic equilibrium, while being coupled with the structural response of concrete. The increase in vapour pressure with rising temperatures, the non-orthogonal fractures of concrete (cracks and spalling) caused by vapour pressure and thermal stress, and the subsequent reduction in vapour pressure were confirmed. Notably, the proper release of vapour pressure after concrete cracking helped to prevent excessive damage. Focusing on the safety assessment of concrete structures, the study also investigated the post-fire performance of a reinforced concrete (RC) shear wall in a nuclear power plant. The proposed model effectively evaluated crack occurrence due to temperature increases, accelerated liquid water and vapour transport, the decrease in vapour pressure from crack propagation, and rapid liquid water penetration during post-fire-curing. The remaining capacity of the shear wall after 400°C heating was 95%, closely matching experimental results.

Chloride-induced rebar corrosion significantly affects the durability of reinforced concrete engineering structures. The service life in such environment is defined by the time at which a critical chloride content is reached at the reinforcement. For design and maintenance stage prediction of the service life is very crucial. Mechanical loading can significantly impact chloride transport and consequently service life predictions. Therefore, a accurate service life prediction model accounting for multiphysical coupling between chloride ingress and mechanical loading is needed. This study develops a numerical service life prediction model for chloride ingress under sustained mechanical loading. This is accomplished by coupling an elastic scalar damage based mechanical model with chloride diffusion transport model. The coupling accounts for the influence of the local stress-strain field and the damage on the effective diffusion coefficient. The numerical model resolves coarse aggregates (meso-scale) to capture the heterogeneous nature of concrete. Consistent distribution function of input parameters are used to enable probabilistic service life analysis by Monte Carlo method. The developed model is applied to a hypothetical case study which demonstrates a first service life
prediction considering different loading scenarios of concrete structures.