Concrete inevitably contains microcracks, but their significance on transport properties and long-term durability is not well established. This is because of difficulties in isolating and evaluating the effect of microcracks whether by laboratory experiments or computer simulations, owing to their complex heterogeneous nature. In this paper, a three-dimensional numerical approach to simulate mass transport properties of concrete containing microcracks is presented. The approach is based on finite-element method and adopts aligned meshing to improve computational efficiency. The mesostructure of concrete is represented by aggregate particles that are surface meshed by triangulation and porous cement paste matrix that are discretised with tetrahedral elements. Microcracks are incorporated as interface elements at the aggregate-paste interface or at the cement paste matrix spanning neighbouring aggregate particles. The main advantage of this approach is that the smallest microcracks can be simulated independent of the discretisation size. The model was first validated by comparing the simulations to available analytical solutions. Then, the diffusivity and permeability of a range of concretes containing different amounts of microcracking with increasing complexities were simulated. The results are analysed and discussed in terms of the effect of microcrack type (bond, matrix), volume fraction, width, specific surface area and degree of percolation on transport properties.

This paper presents a numerical investigation into the effect of ITZ and aggregate shape on the diffusivity of mortar and concrete using a three-dimensional model. Concrete is treated as a three-phase composite consisting of aggregate particles, bulk cement paste and aggregate-paste interface, i.e. the 'interfacial transition zone' (ITZ). The model is set up in two stages. First, a three-dimensional representative volume element of the concrete mesostructure is generated. Then, a finite difference method is used to simulate molecular diffusion through the mesostructure. The transport properties of the conductive phases (bulk cement paste and ITZ) are determined based on the water/cement ratio, degree of hydration and porosity gradients away from aggregate particles. The model is validated against available experimental data and compared with analytical relationships for ideal cases. The model is then used to study the effect of aggregate shape on diffusivity, which has not been attempted before in three-dimensions. The model is also applied to assess the effects of water/cement ratio, degree of hydration, aggregate size, volume fraction, shape and orientation, ITZ width and percolation on diffusivity. Some of these effects are impractical to quantify from laboratory experimentation alone. It was found that the shape and orientation of aggregate particles have a significant effect on diffusivity. Diffusivity decreased when spherical aggregate particles are replaced with ellipsoidal particles due to the consequent increase in tortuosity of the cement paste.Keywords: Concrete; Mortar; Cement-based materials; Modelling; Diffusivity; Aggregate shape Highlights:• Diffusivity of cementitious materials is modelled using a three-dimensional model.• The required characteristics of Representative Elementary Volume were investigated.• The simulations were verified by comparing with experimental and analytical results.• The effects of different variables influencing diffusivity were investigated.• The diffusivity decreased with the increase of aspect ratio of aggregate particles.

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.

In this study, undrained capacity of suction piles subjected to moment loading is examined using three-dimensional finite element analysis. The model was initially validated against well-established results in literature. The model was then used to investigate the effect of moment loading on vertical and torsional capacity by performing a sensitivity analysis by varying soil heterogeneity and suction pile geometry. The parametric study was carried out for suction piles with length to diameter ratios (L/D) varying from 1 to 7 embedded in soils with constant and linearly varying shear strength. The failure envelopes presented provide a better understanding and a simpler and quicker design method that can be readily used for the design of suction piles.

No abstract