An experimental method for assessing the spalling sensitivity of concrete mixture submitted to high temperature

In concrete exposed to high temperatures, two inseparable processes arise: a “thermo-mechanical” process in which the gradient of thermal deformation generates stresses and a “thermo-hydrous” process that generates a driving force for flow of vapour and liquid water. Explosive spalling, especially caused by the latter process, can appear for some kinds of concrete under some heating circumstances, including exposure to fire. To detect the explosive spalling sensitivity of a concrete mixture, a simple test on spherical specimens is proposed and justified. The studied mixtures are high performance concrete with or without polypropylene fibres. Two different curing methods are used and the size effect is analysed. The data recorded are the specimen mass, the temperatures on the surface and in the centre, and the pressure. This exploratory work provides the following elements: a critical percentage of polypropylene fibre avoids spalling with little scattering and smaller sphere diameters accentuate the thermo-hydrous process.