In relation to the sudden and generalized occurrence of potholes observed on pavements subsequently to rainfalls and freezing temperatures, this paper is focused on studying the behavior of partially-water-saturated asphalt concrete (AC) under freezing conditions. Most of previous work on that topic has been devoted to the damaging effect of repeated frost/thaw cycles on wet AC, viewed through the loss of stiffness of the material. The novel aspect presented in this paper deals with the characterization and modeling of the swelling strain effect induced by solidification of pore water at negative temperatures. Transposed to the case of a pavement, we believe indeed that this effect is prone to generate tensile stress at interfaces between AC layers and to generate delamination at short term, ending up into potholes. The present research is a first step towards assessment of this assumption by means of future experimental and numerical analyses at the structural level. Investigations reported in this paper rely on two types of experimental test carried out in the laboratory. The first is performed under free stress condition while the other is subjected to restrained strain. The experimental results from these two tests show the development of significant swelling strains and induced stresses in the partially saturated asphalt specimens, respectively. These two effects are attributed to the phase change of pore water from liquid to solid. A constitutive law taking into account viscoelasticity of AC, thermal expansion and swelling induced by frost is elaborated. This law is implemented in a numerical program and validated against the experimental results. In particular, it is shown that this law is able to make the connection between the magnitudes of the swelling strain and the frost-induced stress stemming from the two tests.