Theoretical model for the characterisation of heat transfer in flexible pavements: field investigation on airfield pavements

Analysis of the influence of temperature on the mechanical and rheological properties of the mixtures used in the bituminous layers of flexible pavements is very important for the choice of materials and correct design of these structures. For this reason, a model has been studied in order to quantify the variation of temperature in bituminous concrete road and airfield pavements, in relation to the climatic conditions. The model developed gives the temperature profile in the pavement (mono-layer as well as multi-layer schematised) at depth at any hour of the day or day of the year, starting from a few climatic parameters that are very easy to obtain: air temperature, solar irradiance at ground level; wind speed next to the pavement. It also considers cloud cover as well as the radiation thermal exchange between the pavement and the air. The temperature of the pavement surfacing can be unknown. The model demonstrated that the pavement schematisation is not so important in the analysis while the heat transmission is unidirectional. Its application is possible whatever the type of flexible pavement and geographical location. After calibrating the model on the basis of data available in the literature (from America and Asia), a field investigation has been carried out in airfields, because airfield pavements are usually formed by much thicker bituminous layers than road pavements. In an airfield pavement in north-eastern Italy (which was in a steady thermodynamic state), thermocouple devices were inserted at various depths and the thermal state monitored in the bituminous layers. The model appears to be reliable for the preventive characterisation of the thermal condition of flexible pavements.