Effect of Wetting-Drying Cycles on Mass and Deformation of Cement and Emulsified Asphalt Mortar
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摘要: 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.Abstract: 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.
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Key words:
- CA mortar /
- wetting-drying cycle /
- mass change /
- deformation /
- pore structure
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图 1 不同干湿循环制度下CA砂浆质量变化
Figure 1. Mass change of CA mortar in different wetting-drying cycles
图 2 不同干湿循环制度下CA砂浆变形曲线
Figure 2. Deformation curves of CA mortar under wetting-drying cycles
图 3 不同干湿循环制度下CA砂浆样品的DSC曲线
Figure 3. DSC curves of CA mortar in different wetting-drying cycles
图 4 不同干湿循环制度下CA砂浆孔径分布
Figure 4. Pore size distribution of CA mortar after different wetting-drying cycles
表 1 CA砂浆配比与新拌砂浆性能
Table 1. Mix proportion and properties of fresh CA mortar
乳化沥青/g 干粉料/g 水灰比 沥灰比 流动性/s 含气量/% 表观密度（g•cm–3） 500 1 100 0.79 0.83 21 9.00 1.61 
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表 2 干湿循环周期设计
Table 2. Design of wetting-drying cycles
项目 制度 A B C D WI AD 干燥时间/d （（20 ℃，65% RH）恒温恒湿箱 ） 3 7 14 28 水浸泡时间/d （20 ℃，自来水） 3 7 14 28 长期 长期 循环周期/d 6 14 28 56
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表 3 4种制度下CA砂浆中结合水及碳酸钙含量
Table 3. Content of bound water and calcite in CA mortar exposed to four exposure conditions
制度 化学结合水/% 碳酸钙/% AD 14.0 21.1 A 16.2 26.6 B 17.5 24.3 C 17.8 24.9 D 18.9 23.4 WI 21.2 15.7
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表 4 不同干湿循环制度下k及D值
Table 4. Slope of fitting line (k) & fractal dimension of pore volume (D) in different wetting-drying cycles
名称 制度AD 制度A 制度B 制度C 制度D 制度WI k 0.56 0.55 0.54 0.54 0.46 0.42 D 2.44 2.45 2.46 2.46 2.54 2.58
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