Computational investigation of capillary absorption in concrete using a three-dimensional mesoscale approach

Abstract

In many exposure environments, capillary absorption of water controls the rate of deterioration of concrete. This paper presents a three-dimensional numerical investigation of capillary absorption by treating concrete as a heterogeneous composite discretised into a cubic lattice. The lattice elements were considered as conductive "pipes" with transport properties assigned based on the phase they represent. The capillary absorption process was described by a non-linear diffusion equation, with the hydraulic diffusivity a non-linear function of the degree of saturation of the composite. A non-linear finite element method was used to solve the governing differential equations. The numerical results were validated against analytical approximations, as well as experimental data from the literature. A sensitivity analysis was then performed to evaluate the effect of heterogeneities produced by aggregate particles on the absorbed water profile and the sorptivity coefficient. It was found that water penetrates concrete in an uneven profile influenced by the amount, spatial distribution and shape of the aggregate particles. Sorptivity decreased when spherical aggregate particles were replaced with ellipsoidal particles due to the consequent increase in tortuosity of the cement paste. This effect increased with increase in aspect ratio and volume fraction of aggregate. However, the size of aggregate particle appears to have an insignificant influence.Keywords: Concrete; Cement-based materials; Lattice-Network model; Unsaturated flow; Capillary absorption; Aggregate shape; Sorptivity Highlights:• Capillary absorption in concrete was simulated using a three-dimensional model.• Simulations were verified by comparing with experimental results and analytical approximations.• Effects of different variables influencing capillary absorption were investigated.• Sorptivity decreased with an increase in the aspect ratio of the aggregate particles.

Relationship between sorptivity and capillary coefficient for water absorption of cement-based materials: theory analysis and experiment

“…Published by the Royal Society under the terms of the Creative concrete structures begin to deteriorate when they are in service for several years, owing to factors such as chloride attack, sulfate attack, frost, carbonation, alkali-silica reaction and so on [4][5][6][7][8][9]. During the process of deterioration, water directly participates in much physical deterioration and indirectly takes part in chemical deterioration as a medium of aggressive ions transport [8][9][10][11]. Therefore, the study of water transport in cement-based materials is the basis for their durability research, and it is of great significance to evaluate the properties, predict the service life and improve the design level of durability [10][11][12][13][14].…”

Influence of formwork material on transport properties of self-consolidating concrete near formed surfaces

“…12) seem to be the main explanation for the lower sorptivity of concrete cover observed in the case of SCC formed against PW surfaces compared to PVC surfaces. Indeed capillary pores exist only in the cement matrix [30][31][32]; the presence of locally high volume of coarse aggregate leads to a lower paste content, thus diluting the volume of the porous media through which absorption could occur [7] and delays penetration of water due to the increased tortuosity. …”

“…Due to the presence of a formed surface, the change in packing of aggregate at the boundary layer against that surfaces (also known as the wall effect) can affect the in-situ transport properties [7]. Kreijger [8] showed that in the case of conventional vibrated concrete, the material found in the first 5 mm near the formwork is essentially composed of mortar with a water-to-cement ratio (w/c) greater than that found in the bulk concrete.…”

Research on the Thermal Properties of Fireplace Concrete Materials Containing Various Mineral Aggregates Enriched by Organic and Inorganic Fibers

“…Concrete is a multi-phase and complex system. Therefore, numerical methods based on multi-species modeling seem very promising for the analysis of concrete [20]. Numerical simulations have been widely used to analyze the influence of aggregates on the transport properties in concrete, including heat transport.…”