Abstract
Concrete diffusivity is a function of its microstructure on many scales, ranging from nanometres to millimetres. Multi-scale techniques are therefore needed to model this parameter. Representative elementary volume (REV), in conjunction with the homogenization principle, is one of the most common multi-scale approaches. This study aimed to establish a procedure for establishing the REV required to determine cement paste diffusivity based on a three-step, numerical-statistical approach. First, several series of 3D cement paste microstructures were generated with HYMOSTRUC3D, a cement hydration and microstructure model, for different volumes of cement paste and w/c ratios ranging from 0.30 to 0.60. Second, the finite element method was used to simulate the diffusion of tritiated water through these microstructures. Effective cement paste diffusivity values for different REVs were obtained by applying Fick’s law. Finally, statistical analysis was used to find the fluctuation in effective diffusivity with cement paste volume, from which the REV was then determined. The conclusion drawn was that the REV for measuring diffusivity in cement paste is 100x100x100 μm 3 .
Highlights
Water diffusion is one of the most important determinants of deterioration in cement-based materials induced by processes such as chloride ion transport or leaching (1)
Predicting concrete diffusivity remains a challenge because of its complex microstructure, which is largely governed by the initial proportions in the mix and ongoing curing conditions (2, 3)
Cement paste itself can be viewed as a random heterogeneous multiphase composite with capillary pores, unhydrated cement particles and hydration products
Summary
Water diffusion is one of the most important determinants of deterioration in cement-based materials induced by processes such as chloride ion transport or leaching (1). Concrete diffusivity is a function of its microstructure on scales ranging from nanometres (pores) to millimetres (aggregate) (4). Concrete/mortar can be regarded to be a random heterogeneous multiphase material containing cement paste, aggregate and an interfacial transition zone (ITZ). Cement paste itself can be viewed as a random heterogeneous multiphase composite with capillary pores, unhydrated cement particles and hydration products. In the approach adopted in the present study, microscale cement paste diffusivity was computed first, based on the 3D microstructure of the paste. The results were used as input to determine mesoscale mortar/concrete diffusivity
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