干湿循环对CA砂浆质量与变形的影响

CA砂浆（cement and emulsified asphalt mortar）服役环境湿度因气候、天气因素的影响产生显著变化，会引起其质量和体积的变化，进而对轨道结构的几何尺寸产生影响. 为了解服役环境中湿度变化对CA砂浆质量、尺寸的影响，设计了6种干湿循环制度，测试了不同干湿循环制度下CA砂浆质量、长度变化；并采用低场核磁共振（NMR）及综合热分析（TG-DSC）对其孔结构和物相组成进行了分析，以揭示其变化机理. 研究结果表明:随着循环次数的增加，CA砂浆湿质量迅速增加并达到最大值，随后下降，并在140 d左右趋于稳定，干质量的变化很小；而其长度随循环次数的增加先减小后增加. 干湿循环中，CA砂浆质量与长度的变化均小于持续干燥、水浸泡条件下的变化. 在短周期干湿循环中，在约140 d前，CA砂浆湿质量与变形呈二次函数关系，而在约140 d后，质量与变形呈线性关系；在长周期中，二者相关性不强. NMR与DSC的分析结果表明，CA砂浆质量与长度变化是干湿循环过程中毛细孔水分的迁移、水泥水化、碳化以及孔结构变化等因素共同作用的结果. 

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.