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Journal of Zhejiang University SCIENCE A

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Multi-field, time-varying behavior, and cracking mechanisms of early-age concrete in balastless track beds

Author(s): Xiao LI, Juanjuan REN, Shijie DENG, Zeyong ZHANG, Xueyi LIU
Affiliation(s): MOE Key Laboratory of High-speed Railway Engineering, Southwest Jiaotong University, Chengdu 610031, China; more
Corresponding email(s): jj.ren@swjtu.edu.cn
Key Words: Ballastless track; Early-age concrete; Hydro-thermo-chemo-mechanical coupling; Early cracking of track bed

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Abstract: Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties, environmental effects, and construction processes. This is a multi-field, time-varying issue involving hydro-thermo-chemo-mechanical coupling. However, to date, research has not adequately described the early-age cracking mechanisms in track beds, and few risk control measures have been proposed. To solve this problem, we incorporated the hydration degree of concrete into multi-field coupling equations for early-age concrete, and set boundary conditions that account for environmental influences and various stress factors that typically cause early creep of concrete. A four-field coupled risk prediction model was built based on hydro-thermo-chemo-mechanical properties, and was used to calculate and analyze various time-varying behavior (including the risk and form of cracking) in the hydro, thermo, chemo, and mechanical fields of early-age concrete. Finally, we focused on material-related factors (maximum heat of hydration and peak heat release time), environmental factors (temperature difference between day and night, average daily cooling rate, and intensity of solar radiation), and construction technique factors (molding temperature, pouring time, and thermal insulation coefficient). The influence of these factors on the early-age cracking risk of the track bed was analyzed, and risk control measures against early cracking were proposed accordingly.

早期道床多场时变行为及开裂机理研究

作者：李潇^1,2，任娟娟¹，邓世杰¹，张泽墉¹，刘学毅¹
机构：¹西南交通大学，高速铁路线路工程教育部重点实验室，中国成都，610031；²中国五冶集团有限公司，中国成都，610063
目的：无砟轨道现浇混凝土部件，尤其是双块式轨道整体现浇道床，在材料不良、环境不利、施工不当等多种因素影响下，早期开裂问题频发。本文旨在建立一个更为完善的早期道床开裂风险预测模型，在此基础上研究早期道床多场时变行为和开裂机理，探寻早期道床开裂风险影响规律并提出合理的开裂风险管控措施。
创新点：1.建立更完善的早期道床开裂风险预测模型，且模型假设条件更少，准确性更高，适用场景更全面；2.系统分析道床早期多场耦合时变规律和开裂机理；3.揭示材料、环境以及施工三类因素对混凝土道床早期开裂风险的影响规律，并提出了道床早期开裂控制措施。
方法：1.通过理论推导，统一混凝土早期到成型全过程的水化-热-湿-力耦合多场控制方程，并建立早期道床开裂风险预测模型；2.通过数值模拟，得到道床早期多场耦合时变规律和开裂机理，并揭示不同因素对混凝土道床早期开裂风险的影响规律。
结论：1.在典型工况条件下，在水化场方面，道床最大水化速率出现在浇筑后约7.0 h；道床终凝点在浇筑后约9.5 h；道床水化在第7 d的水化进程可达最终水化度的90%。在温度场方面，对流换热和太阳辐射是影响道床早期温度场的主要环境因素；道床表层最高温度浇筑后约16.0 h达到最大值，比入模温度高约15.0 °C。在湿度场方面，早期道床内双块式轨枕附件存在局部不均匀湿度区域。在力场方面，约在第1.25 d，轨枕四周新老混凝土结合面开裂的风险系数已超过1.00；在第7 d，轨枕附近道床八字形裂纹的开裂风险达到最大，风险系数约为0.75。2.温度变形是道床表层开裂的主导因素，也是道床板底开裂的主要驱动力；如果不考虑道床混凝土早期徐变，会大幅度高估开裂风险，因此建模时应当考虑徐变的影响。3.综合性的早期道床开裂风险控制措施方面，建议按照优先级降低的顺序（水化热→优化放热峰值时刻→增强保温措施→选择合理浇筑时刻→控制入模温度），进行早期道床混凝土开裂控制。

关键词组：无砟轨道；早期混凝土；水化-热-湿-力耦合；道床早期开裂

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早期道床多场时变行为及开裂机理研究

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