Multiscale modelling of concrete durability: From microstructure to macro-scale properties

Concrete is the most widely used man-made material in the world.

During its service life, reinforced concrete may interact with its environment and suffer from various types of degradation, such as chloride-induced corrosion of reinforcing steel, carbonation and so on.

As a result, a large percentage of the total infrastructure budget is spent on the repair and maintenance of concrete structures. All these degradations are related to transport phenomena in concrete, for example the ingress of chloride ions, O2 and CO2 into concrete. This means that transport properties of concrete including diffusivity and permeability are usually considered as indicators to assess the durability and predict the service life of reinforced concrete structures. Transport properties of concrete depend on the evolution of concrete’s underlying microstructures over a wide range of length scales.

In this work, for the first time, the transport properties of saturated and unsaturated concrete are investigated from a multiscale point of view. A range of advanced experimental techniques including X-ray micro-CT, a scanning electron microscope, and computer based models are used to characterise the internal microstructure of concrete. An integrated multiscale lattice Boltzmann-finite element modelling scheme from micro- to meso-scale is developed (based on the 3D microstructure that was developed). The modelling scheme is applied to simulate single- and multi-phase flow in concrete, which is then used to determine transport properties as a function of both the moisture content and pore structure features.

This research makes it possible to accurately predict the service life of reinforced concrete and thus support decision-making by government and industry on the enhancement of durability concrete structures. The multiscale approach we have developed opens up the potential for a wider variety of applications outside cement-based materials, such as petroleum engineering and geosciences, waste containment and disposal, fuel cell and so on.

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