Influence of aggregate shapes on drying and carbonation phenomena in 3D concrete numerical samples

Abstract

This study aims at generating numerical 3D samples of concrete so as to study the effects of the granular inclusions shape on the macroscopic kinetics of reactive transport phenomena.Two types of mesostructure configurations are considered: the first one is composed of a matrix of mortar in which are randomly distributed inclusions corresponding to the concrete coarse aggregates, and the second one also includes a steel rebar. The choice of a mesoscopic modeling for the mortar matrix is based on the need to obtain numerical structures of reasonable size. In particular, the Interfacial Transition Zones (ITZ) are ignored, as this hypothesis seems acceptable for coarse aggregates. This study is applied to the case of drying and atmospheric carbonation by using simplified models solved by the finite element code Cast3M. The purpose is to quantify the influence of the aggregate shape on the kinetics of macroscopic transfer and the isovalue lines for some physical variables representative of the reactive transport problems: saturation degree for drying, and porosity, calcite and portlandite concentrations for carbonation. Basic aggregates shapes are studied (spheres, cubes), as well as more complex ones (Voronoi particles) which are supposed to be more representative of real aggregates. The effects of 'non-isotropic' shapes (oblate and prolate ones) are also investigated. It is shown that the influence of the aggregate shapes appears negligibly small on macroscopic indicators, except for oblate shapes with aspect ratios of 3. This latter case also exhibits substantial local delayed effects and a more important variability, which may have some importance for a precise description and estimation of degradation processes related to steel rebar corrosion.

Coupled carbonation-rust formation-damage modeling and simulation of steel corrosion in 3D mesoscale reinforced concrete

“…However, calcite progressively formed around the portlandite crystals becomes a diffusive obstacle for carbonate and calcium ions, leading to reducing the kinetic constants of the calcite formation reactions (se e.g. [25,26,31]). There exists a direct coupling between carbonation and drying through saturation degree and porosity, which appear in both mass balance equations.…”

“…Instead, the hypothesis that the calcium dissolved from portlandite and the other hydrates is locally transformed into calcite, constituting a local chemical equilibrium, is adopted. For further details, the reader may refer to [26].…”

“…The coupled drying and carbonation of concrete are described by a simplified model, initially proposed in [24] and modified and improved in [25] and [26]. This model assumes that the main phenomena involved in the carbonation are the water transport through the connected porosity, the diffusion of carbon dioxide in the gaseous phase and its dissolution followed by the reaction with portlandite and other hydrated phases to form calcite.…”

“…This model assumes that the main phenomena involved in the carbonation are the water transport through the connected porosity, the diffusion of carbon dioxide in the gaseous phase and its dissolution followed by the reaction with portlandite and other hydrated phases to form calcite. The formulation rests on two coupled nonlinear mass balance equations for the water and the carbon dioxide in gaseous phase, respectively, expressed as [26]:…”

Numerical Simulation on Carbonation Depth of Concrete Structures considering Time‐ and Temperature‐Dependent Carbonation Process

“…e environmental factor includes relative humidity [11][12][13][14], and the compositions include water-cement ratio [15], various supplementary cementing materials [16][17][18], aggregates [19,20], and mix proportions [21,22]. In these studies, there are few researches about the carbonation situation on the carbonation surface.…”