X-ray µCT imaging allows observing the evolution of the water content in asphalt over time, at least for small samples. Since it is a three-dimensional measurement, root causes for discontinuities in the evaporation rate can be investigated. Indications were found that the evaporation depends not only on global proprieties like mean pore volume and diameter but also on the detailed structure of the pore network. In particular, blocking water lids formed by surface tensions at the outer boundary of the sample appear to have a strong influence on the evaporation rate. Actually, similar phenomena were studied in silicon microstructures (Litborn and Roeraade, 2000). However, a simulation of the evaporation of water in porous asphalt taking into account the exact geometry is required to understand all the mechanisms determining the evaporation rate