Moisture and size dependence of thermal deformation in cement and asphalt mortar

Cement and asphalt (CA) mortar is a key structural material for high-speed railway slab ballastless tracks. To investigate the deformation property of CA mortar in the range of − 20–60 °C, a DIL402C thermal expansion instrument and a self-designed thermal deformation tester were used in this paper, and the thermal deformation mechanism was revealed by combining the dynamic thermal analysis technology, the relationship between the deformation and mass under cyclic temperature variation, and the microstructural testing. The results indicated that the thermal expansion deformation of CA mortar decreased as the moisture content increased. Under vacuum-drying, air-drying, and water saturation state, the thermal expansion strain ranges of CA mortar specimens with different sizes were 1.0248–1.4340 × 10^–3, 0.4438–1.3669 × 10^–3, and − 2.1815–0.5571 × 10^–3, respectively. The smaller the specimen size, the more significant the thermal shrinkage deformation caused by the increased humidity. The thermal expansion coefficient of CA mortar increased gradually during the initial heating process and then changed in a complicated manner with changes in the humidity. As a porous material with asphalt as the continuous phase, when the temperature increases, the volume expansion of ice, the melting of ice into water, the migration and evaporation of water, the phase change of asphalt, and the volume expansion of cement mortar jointly affect the overall deformation property of CA mortar.