Thermal contraction is a key factor in low-temperature cracking, contributing to internal stresses in the bitumen-aggregate composite. Most macromechanical models treat mastic as a continuous material, limiting an in-depth analysis of the component interactions, which is essential for improved material design. This study analyses the low-temperature behaviour of bitumen and mastic containing different basalt filler content using experimental testing and micromechanical finite element modelling (FEM). The model evaluates micromechanical interactions between bitumen and aggregates, with aggregates modelled as spherical particles in the bitumen. Thermal contraction coefficients are predicted via viscoelastic modelling and compared to experimental results. Findings show higher filler content lowers the thermal contraction coefficient while increasing stress concentrations due to the combined thermal properties of bitumen and filler. The micromechanical model aligns well with experimental data, confirming its reliability in predicting stress distribution and thermal behaviour. These insights enhance the understanding of bituminous materials in cold environments.