This research aims to model ASR gel expansion in concrete under the influence of hygral and thermal loading. ASR provokes a heterogeneous expansion in concrete leading to dimensional changes and eventually the premature failure of the concrete structure. Factors that influence ASR are parameters like cement alkalinity, the amount of deleterious silica from aggregate, porosity, and external factors like temperature, humidity and external source of alkali from ingression of de-icing salts. The problem is formulated as a multi-field problem, combining heat and fluid transfer and the damage model with mechanical stress field. Simulation is performed as a mesoscale model considering aggregates and mortar matrix. Expansion strain values will be determined from concrete prism tests. The resulting model will be able to predict the rate of ASR expansion and the cracking propagation that arise.