Chloride Ion Transport in Concrete of Ballastless Track under Fatigue Loading
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摘要: 疲劳荷载作用下，无砟轨道混凝土的抗氯离子渗透性能是影响其服役特性的主要因素之一. 为分析混凝土在疲劳荷载作用下氯离子的传输变化规律，首先针对浸泡于氯离子溶液的混凝土试件进行弯曲疲劳试验，然后利用COMSOL有限元软件建立结构力学场与氯离子传输场的两场耦合模型，模拟氯离子在混凝土中的扩散行为. 研究结果表明：当侵蚀时间为2 d时，应力比为0.3、0.5和0.7对应的氯离子扩散深度分别为7、11、16 mm，混凝土中氯离子扩散深度随荷载应力比的增大而增大；两场耦合有限元模型计算得到的氯离子含量与试验测试结果基本吻合，验证了模型的合理性；混凝土中氯离子扩散深度随侵蚀时间的增大而增大，采用一元二次多项式可较好地描述扩散深度与侵蚀时间的关系.Abstract: The chloride ion penetration resistance of concrete structure of ballastless track under fatigue load is one of the main factors affecting its service performance. In order to analyze the variation of chloride ion transport in concrete under fatigue load, the bending fatigue loading test of concrete specimens immersed in chloride solution was carried out. A two-field coupling model based on the structural mechanics field and the chloride transport field was then established with COMSOL finite element software to simulate the chloride diffusion behavior in concrete. The results show that when the erosion time is 2 d, the chloride ion diffusion depths corresponding to the stress levels of 0.3, 0.5, and 0.7 are 7, 11 and 16 mm, respectively, which indicates that the chloride diffusion depth in concrete increases with an increase in fatigue stress level. The chloride ion concentration calculated by the two-field coupling finite element model is basically consistent with the experimental test results, which proves that the model is reasonable. What’s more, the diffusion depth of chloride in concrete increases with the erosion time, and the relationship between them can be described well by a unary quadratic polynomial.
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Key words:
- ballastless track /
- concrete /
- chloride ion transport /
- fatigue load
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图 3 疲劳荷载下混凝土中氯离子传输试验
Figure 3. Chloride ion transport test in concrete under fatigue loading
图 4 不同加载频率下氯离子扩散系数（a=0.3）
Figure 4. Chloride diffusion coefficient at different loading frequency (a=0.3)
图 6 不同应力比下跨中截面氯离子含量分布
Figure 6. Distribution of chloride ion concentration in the mid-span section under different stress levels
图 7 不同应力比下模型计算值与试验值对比
Figure 7. Comparison of calculated and experimental values under different stress levels
图 8 不同应力比与侵蚀时间下氯离子含量变化
Figure 8. Changes in chloride ion concentration under different stress levels and erosion times
表 1 试验模拟工况
Table 1. Test simulation conditions
工况 应力比 a f/Hz 模拟车型 1 0.3 10 低速货车 2 0.3 15 低速客车 3 0.5 15 普速货车 4 0.7 15 普速货车（极限设计值） 5 0.3 20 普速客车 
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表 2 COMSOL中试件的力学参数
Table 2. Mechanical parameters of the specimen in COMSOL
参数名称 取值 弹性模量/（× 1010 Pa） 3.8 泊松比 0.2 抗压强度/MPa 69.2 极限荷载/kN 29.3 密度/（kg•m−3） 2 303
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表 3 扩散模型相关参数
Table 3. Parameters of diffusion model
参数名称 取值 f/Hz 0.15 氯离子溶液质量分数 C 0.10 T/°C 0.28 初始氯离子质量分数 C0 2.42×10−4 t/d 2 表面氯离子质量分数 C1 0.001 46 ${\phi _0}$/% 4 水灰比 0.35 时间衰减因子 m 0.3
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