It is not fully understood how corrosion-induced cracking in reinforced concrete is affected by corrosion rate. Improved understanding of this effect is important because it assists with predicting the state of structures which suffer from corrosion-induced cracking based on results of accelerated laboratory tests with confidence. Possible reasons for the effect of corrosion rate on corrosion-induced cracking are creep of concrete, migration of corrosion products into pores and cracks, and composition of corrosion products. Here, we test the effect of creep. We carry out corrosion experiments on specimens consisting of a single reinforcement bar embedded in a concrete cylinder. We vary corrosion rates and water-cement ratios of concrete. The modelling of corrosion-induced cracking is carried out with a lattice approach based on a visco-elastic damage-plasticity constitutive model which predicts the effects of linear creep, but not the migration of corrosion products nor the effect of corrosion rate on corrosion products. With this choice of model, we test if creep together with fracture can reproduce the effects of water-cement ratio and corrosion rates. Based on our experimental results, corrosion penetration at a fixed surface crack width increases with decreasing corrosion rate and increases with increasing water-cement ratio. The lattice approach with fracture and creep but without corrosion product migration is not able to reproduce the dependencies of rate and water-cement ratio on critical corrosion penetration satisfactorily.

The prediction of the leakage rate of containment vessels in double-walled nuclear power plants is of particular importance given the role of the structure. As the third containment barrier, it must indeed guarantee a certain level of leak tightness in order to perform its function fully. Traditionally, the estimation of the leakage rate is based on simulation and includes a good knowledge of the hydric state (degree of saturation) and of the potential mechanical disorders (potential cracks). These quantities are then associated with transfer laws (generally damage - or crack opening - permeability) in a chained (thermo)hydric/mechanical approach. This paper describes the evolutions in the methodology used to predict the mechanical behavior of containment buildings, for which numerous developments have been made in recent years. After introducing a brief history of mechanical behavior simulation practices at this scale (direct application of damage mechanics for example), significant improvements, in terms of representativeness and performance of the mechanical calculation, will be discussed. A particular attention will be paid to scale change using evolving static condensation, from the containment buildings to Representative Structural Volume, on which the application of more refined approaches become possible. Finally, discussions on open issues are proposed towards simulating the behavior of a real structure.

Crack pattern induced by alkali-silica reaction (ASR) varies depending on environmental conditions, which affects the mechanical properties of concrete. This study aims to investigate the change in mechanical behaviors of ASR-damaged concrete with respect to acceleration temperature and crack pattern. Cylinder specimens were fabricated and immersed in 1 mol/L NaOH solution at two different temperatures, 40℃ and 60℃, for ASR acceleration until the expansions reached 0.25% and 0.50%. Subsequently, a cyclic compression test was performed to identify the elasticity and plasticity as well as the compressive strength and elastic modulus. In addition, using fluorescence epoxy-impregnated samples in each specimen, crack patterns due to ASR were observed under ultra-violet (UV) light and quantitatively analyzed through image analysis. The expansion rate of concrete stored at 60℃ was higher than that at 40℃, depending on which different ASR crack pattern and elastic modulus appeared. Large cracks were more prevalent in the specimen immersed at 40℃ than that at 60℃, and the reduction in elastic modulus of the specimen immersed at 60℃ was less than that at 40℃. The fracture parameters representing the remaining shear elasticity were calculated based on the measured elastic and plastic strains, and the results indicated that the fracture parameter of the specimen immersed at 40℃ was slightly lower than that at 60℃.

Concrete is considered a heterogeneous material composed of aggregates enclosed by a mortar matrix. The Finite Element analysis is performed by inserting zero-thickness interface elements in between continuum elements along pre-selected paths representing main potential crack paths. These interface elements are equipped with a fracture-based constitutive law. In previous literature this approach has been shown to provide very realistic results in the study of concrete fracture. Moreover, remeshing becomes unnecessary by the a-priori insertion of these elements where the fracture capability is concentrated, and the problem of localized deformation in the continuum elements is also overcome. However, using this approach a duplication of nodes occurs along the surfaces where they are inserted, and this may lead to a very high computational effort. In recent years, the group of Mechanics of Materials at UPC has devoted substantial effort to extend the applicability of such approach to a variety of coupled problems, and to increase its efficiency via MPI parallelization and PETSC libraries. In particular, these improvements have also been applied to the 3-D analysis of concrete specimens subject to external sulphate attack. In this context, the paper describes the coupled C-M model, presents the latest results obtained with various meshes of progressively larger sizes, and shows the scalability of the parallel implementation developed. Additionally, the paper describes a new technique developed to reduce computation times, consisting of identification of continuum blocks surrounded by interface elements and eliminating internal nodes using a Schur complement scheme. The new strategy has only been implemented so far in sequential mode, but results are presented that lead to significant reduction in computation time, and work is under way to achieve full parallel version of this technique.

This paper summarizes the authors’ previous work on modeling and numerical simulation techniques for concrete residual mechanical performance evaluation, which has expanded owing to various factors, including alkali-silica reactions (ASRs), frost damage, and delayed ettringite formation (DEF). By varying the mechanical constitutive law and expansion strain proportion considered according to the different crack characteristics and time-dependent properties caused by each type of expansion deterioration as well as substance precipitation in the cracks, it is possible to perform numerical simulations that consider the differences in the concrete mechanical properties under various expansion states using a nonlinear finite element method. The relationship between the cracking characteristics and the mechanical performance of the expansive concrete was also verified experimentally. Regarding the ASR expansion, it has been successfully demonstrated via simulations that it is possible to rationally explain both cases, where the structural performance of reinforced concrete members improves after expansion and where it deteriorates, by considering the crack characteristics and reaction speed in the ASR.