As an important maintenance measure, de-icing agents are commonly used to ensure safe surface conditions of highways and airport runways during winter. There are however issues related to their use, such as deteriorating effects on road materials, causing particle loss and a decreased low-temperature stiffness of asphalt pavements. To avoid this, it is therefore important to be able to evaluate the effect of the deicer on the asphalt mixture with reliable results. The European standard method for this, EN12697-41, is however associated with several issues such as a high variability of the results and a lack of consistency with the field. Using both experimental testing and numerical simulations, this paper aims to explain the cause of these and to identify the main dominant parameters which can potentially be modified for an improvement. The experimental testing evaluated both the diffusive properties of de-icing fluid and water in mastic and the standard method itself, and the numerical simulations evaluated the effect of different parameters related to the set-up test. From the evaluations, it was concluded that both the set-up of the test and the geometry of the test sample contribute to the high variability of the test method and its lack of consistency with the field. Recommendations are therefore made regarding the potential for improvement and further evaluation of the method.