A new model for corrosion-induced cracking in reinforced concrete is presented [1,2]. Corrosion of steel in concrete is responsible for 70-90 % of prematurely deteriorated reinforced concrete structures and can even cause structural failure as infamously documented by recent collapses of aerated concrete panels in British schools. The state-of-the-art knowledge of the underlying processes has been incorporated into three interconnected submodels: (i) a reactive transport model for: (i.A) the transport of water and aggressive corrosion-activating species (such as chlorides or carbon dioxide) to the steel surface and (i.B) the transport iron ions released from the steel surface in the concrete pore space where they precipitate into rust, (ii) model for the corrosion-induced pressure resulting from the concurrent constrained accumulation of compressible rust in: (ii.A) the dense rust layer in the steel volume vacated by corrosion and (ii.B) in concrete pore space (evaluated with a newly proposed precipitation eigenstrain), and (iii) a phase-field fracture model calibrated to accurately describe the quasi-brittle fracture of concrete. The proposed model was implemented in COMSOL Multiphysics software and solved numerically with the finite element method. Both uniform and non-uniform corrosion case studies were investigated and validated with experimental data. Importantly, the model allows to simulate the impact of the magnitude of the current density on the propagation rate of cracks, which has been puzzling researchers for over 25 years. In addition, for the first time, time-to-cracking for highly porous aerated concrete was investigated.

[1] E. Korec, M. Jirasek, H.S. Wong, E. Martinez-Paneda, Phase-field chemo-mechanical modelling of corrosion-induced cracking in reinforced concrete subjected to non-uniform chloride-induced corrosion, Theoretical and Applied Fracture Mechanics. (2023) 104233.

[2] E. Korec, M. Jirasek, H.S. Wong, E. Martinez-Paneda, A phase-field chemo-mechanical model for corrosion-induced cracking in reinforced concrete, Construction and Building Materials. 393 (2023) 131964.

Concrete is a composite material comprising aggregates and a cement matrix at the mesoscale level. The mesoscale structure of concrete materials can significantly influence the macroscopic mechanical behavior, including failure modes and zones. While the Lattice Discrete Particle Model (LDPM) is a state-of-the-art approach for simulating concrete at the coarse aggregate level, it does not completely capture the heterogeneity between aggregates and the matrix. The LDPM model divides a basic four-particle tetrahedron into four subdomains, with each subdomain encompassing portions of both aggregates and the matrix. However, the original LDPM model simplifies this subdomain as a concrete material with uniform mechanical behavior. Due to this simplification of the actual heterogeneity, the original LDPM does not accurately predict the amount of experimentally observed scatter and spatial variability. To address this critical limitation, this paper introduces a heterogeneous LDPM, termed the two-phase LDPM. The two-phase LDPM considers the subdomain encompassing both aggregates and the matrix, thereby achieving greater realism. The introduced two-phase LDPM is assessed under a variety of stress and loading conditions including tension, compression, and shear by comparing with results obtained from the original LDPM model and experimental data from the literature. The study demonstrates the reliability of the two-phase LDPM, enhancing the predictive accuracy of the original LDPM model and elevating its utility in engineering applications.

Concrete is a highly heterogeneous material that ranges from nanometre to metre scale. To characterise the behaviour of concrete, it is essential to know all the physical and chemical processes that occurs within its constituents to model the physics associated with creep and shrinkage in concrete structures. In the first part of this study, a coupled chemo-hygro-thermo-mechanical model of concrete is developed. Uncertainty tools based on a probabilistic framework are used to model the possible variations in the input variables in the hygro-thermo-mechanical formulation. Uncertainties in the selected set of important variables are reduced using Bayesian inference and short-time measured responses. For validating efficiency of the uncertainty reduction technique adopting Bayesian inference and global response sensitivity, the predictions of creep and shrinkage in concrete are compared with a few experiments from the North-Western University (NU) data base. The uncertainty reduction technique is then used to predict the long-time prestress losses in post-tensioned concrete beams and slabs cast in the laboratory. A hierarchical homogenization technique is used to introduce into the model different scales and validate it with test data. Thereafter the model has been modified to include the effects of the aggregates in the concrete matrix through a mesoscale treatment of the aggregate in a cement mortar matrix and bringing to fore the effects of micro-structural phenomena through a homogenisation-based upscaling technique of cement hydration processes taking place at micro-scale. This makes the multi-physics meso-model length scale dependent. Validation of the present approach with a range of experimental results highlights the robustness of the model in terms of optimum and targeted design of a cementitious material.