Explosive spalling of high performance concrete under fire is one of the major concerns in front of the engineering community today. It is associated with violent failure of thin layers of concrete resulting in sudden reduction of load carrying capacity which may lead to complete collapse. High pore pressures due to low permeability and stresses due to thermal gradients are considered to be the governing causes of explosive spalling. However, the failure mechanisms and all influencing parameters are not yet fully understood. The most popular method to prevent spalling is the addition of polypropylene (PP) fibres in concrete. It is generally accepted that the PP fibres leave a porous network after melting at around 160 °C, leading to an increase in permeability, thus allowing the water vapour to escape. However, it seems that there also might be other mechanisms which lead to relief of pore pressure. This work is aimed at investigating the phenomenon of explosive spalling and understanding the causes behind the same. Technical difficulties in measuring during the experiments at high temperatures or fire limit the data that can be obtained. On the other hand, numerical analysis provides a better insight into the governing causes and a quantitative estimate of the relevant properties. Therefore, in this work, the experimental investigation is augmented by extensive numerical parametric studies. Experiments under two typical fire scenarios are conducted on slabs made of plain and concrete with PP fibres to compare the performance of the two mixes as well as to investigate the effect of the heating rate on explosive spalling. Significant influence of PP fibres in mitigating explosive spalling is confirmed by these experiments. In order to measure the permeability of concrete at elevated temperature, a new test setup is developed and validated. Permeability experiments on plain and concrete with addition of PP fibres are performed at temperatures up to 300 °C using the new test setup. The results show that permeability of concrete with PP fibres rises even before the fibres melt, thus indicating that the melting of fibres is not the only mechanism responsible for the permeability increase. To confirm this, microstructure of the specimens before and after heating is studied using a scanning electron microscope. The existing thermo-hygro-mechanical model is validated against experiments and is used to investigate the influence of various parameters on explosive spalling. The parameters studied include: permeability, relative humidity, restraint, load, inhomogeneity, aggregate type, etc. The numerical parametric studies are performed at macro- and meso-scale. Due to the high influence of the local inhomogeneities, analysis at macro-scale could only partially capture the failure mode. It is found that all aspects of explosive spalling can be considered only while performing analysis at meso-scale.