Effect of Wetting-Drying Cycles on Mass and Deformation of Cement and Emulsified Asphalt Mortar

The varying humidity of service environment due to the change of weather and climate has a significant influence on the mass and volume of CA (cement and emulsified asphalt) mortar, which further influences the geometrical size of track structure. To understand the effect of the variation of ambient humidity on the mass and size of CA mortar in service, 6 kinds of wetting-drying cycles were designed in which the mass and length changes of CA mortar were measured. To investigate the mechanism of length change, pore structure and phase composition were examined by low field nuclear magnetic resonance (NMR) and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC). The results show that with the increase of cycle numbers, the wet mass of CA mortar firstly increases rapidly and reaches the maximum value, then starts to decline, and stabilizes at about 140 days, and the dry mass of CA mortar changes a little; however, the length change exhibits an initial decrease and then increase trend. In wetting-drying cycles, the mass and length changes of CA mortar are less than that under continuous air-drying or water immersion condition. During the wetting-drying cycles with short periods, an evident quadratic function relationship between mass change and deformation of CA mortar can be found before around 140 days, after which the correlation converts into a linear relationship; however, the correlation is not significant during the wetting-drying cycles with long periods. The results obtained from NMR and TG-DSC indicate that the migration of capillary water, hydration of cement, carbonization, and the change of pore structure are the joint reasons accounting for the mass and length changes of CA mortar.