This study examines the thermal performance of concrete incorporating bio-based aggregates modified with polymers and phase change materials (PCM). Four mixes were tested: conventional concrete, concrete with uncoated wood aggregates, with polymer-coated (XSBR) wood aggregates, and with PCM-saturated, XSBR-coated wood aggregates. Spherical specimens (72 mm) were cooled to ~7 °C and then exposed to convective heating (~40 °C), with core temperatures monitored using type K thermocouples. PCM-containing samples exhibited a clear thermal buffering effect, delaying heat transfer during phase transition. Wood aggregates also reduced thermal conductivity compared to conventional aggregates, further slowing heat propagation. A Finite Element Method (FEM) model was developed to simulate heat transfer. While the model accurately reproduced the reference concrete behaviour, discrepancies increased with material complexity due to bio-aggregates, coatings, and PCMs. The simplified approach could not fully capture latent heat dynamics, underscoring the need for advanced modelling techniques for heterogeneous composites with phase change functionality.