Driven by the energy-intensive manufacturing process, cement stands as one of the primary contributors to global carbon dioxide emissions. In an effort to mitigate its environmental impact, civil engineers are substituting traditional Portland cement clinker with materials like silica fume, fly ash, or other supplements. Despite incorporating polypropylene fiber reinforcement in accordance with Eurocode 2, these contemporary cements exhibit spalling tendencies under thermal loading during experiments. The origin of this behaviour remains elusive, due to the multiphysical nature associated with concrete spalling, which proves challenging to study through experimental means alone. Numerical modelling offers a possible solution to this problem as it can provide insight into the specifics of the problem. Within a well developed chemo-thermo-hygro-mechanical framework on the macro scale, the spatial stress developments of blended concretes under fire loading are investigated, considering four primary state variables, i.e., gas pressure, capillary pressure, temperature, displacement and two internal variables, i.e., dehydration degree and chemo-mechanical damage. The dehydration degree of the different blended concretes is predicted by a stochiometric model using Arrhenius equations for each cement constituent. Based on a microporomechanical framework, the chemo-mechanical damage and stress state is calculated via Eshelby-type homoginsation techniques at different scales of observation, namely, concrete, mortar and cement paste. Stresses at different levels are induced by the macroscopic stresses and due to the thermal incompatibility of aggregates and hardened cement paste. Blended concretes, CEM II/A-LL, CEM III/B, CEM II/B-V, CEM II/B-Q, are compared with CEM I regarding the mechanical stress development at different scales in the context of a sensitivity analysis. This paper concludes that the stress development of the thermal incompatibility and hygro-mechanical material properties have an significant influence on the macroscopic behaviour and should be further investigated.