Keywords: convective heat transfer, finite element, alkali-silica reaction, porous media.

The thermo-hygro-chemical model introduced in this paper acts as a preliminary foundation in solving a mechanical response problem in a heterogeneous media like concrete due to the alkali-silica reaction (ASR). ASR induced damage in concrete structures provokes a heterogeneous expansion that will cause dimensional changes in the structure. What sets apart ASR with other concrete phenomenon is that ASR occurs at different concrete regions at different rates, depending on the concrete composition and the external influences, thus making the task of predicting its behaviour difficult. An ability to predict its behaviour and damage mechanism is therefore required.

Heat and moisture transfer in porous media behaves differently than that of solid or liquid media. As concrete is comprised of three main constituents which are the skeleton, pore gas and pore liquid, therefore, heat and moisture transfer in concrete may happen due to all transfer methods (conduction, convection, and/or radiation) simultaneously, therefore making the determination of temperature distribution and ion transport more complex. As all three constituents have its part in the ASR, the interaction between pore gases, pore liquid and solid are equally considered in the modelling. The capability of a numerical simulation in incorporating both modelling and stochastic concepts in a program makes it a suitable tool to generate the expansive pressures and crack propagation due to ASR.

This paper presents a numerical simulation of convective heat transfer in a porous media using the finite element method at the mesoscale. The resulting pressure distribution, together with the ASR expansion strains in concrete will be introduced into an isotropic damage model, where the resulting stress distribution and crack propagation (if any) will be determined. The mesoscale model will finally be coupled in a structural model at a macroscale level to predict the mechanical response of concrete due to ASR with all major influences (temperature, moisture, alkali-silica reactivity) already taken into account. The macroscale model will then be simulated to include the effects of mechanical loading, freezing and thawing, and fatigue. All the models will be simulated using an implicit finite element technique using finite element software. The accuracy of the model will then be compared to the experimental results of the ASR on concrete beams exposed to different solutions.

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