Multi-physics modeling of early-age hygro-thermal-chemical (HTC) fields in the base plate of double-block ballastless track structures considering different curing strategies

Cast-in-situ ballastless track structures are prone to early-age cracking, which seriously affects their durability. Therefore, this paper focuses on investigating the complex multi-physical field distribution of double-block ballastless track structures at early ages. Currently, hygro-thermal-chemical (referred to as HTC model) coupled modeling has not been implemented in large-scale commercial software. This paper demonstrates the application of a recently proposed framework to study the early-age behavior of cast-in-situ double-block ballastless track structures via hygro-thermal-hydration analysis. To investigate the influence of curing methods on multi-physical fields, an additional layer with adjustable thickness was incorporated into the actual model to precisely simulate solar radiation absorption, convective heat transfer, and net thermal radiation at the actual boundary interfaces. The parametric analysis demonstrates that a 3-mm-thick additional layer achieves optimal geotextile curing simulation, while thicknesses of 7 mm and 3 mm are required for plastic film curing and natural curing, respectively. Based on the HTC model, this study also investigates the effects of three methods used at the construction site on the early-age multi-physics fields of the base plate. The results revealed that: when geotextile covering and sprinkling water was implemented, the cement hydration reaction rate reaches its peak approximately 14 h after casting, coinciding with the highest temperature gradient along the vertical direction and the most significant relative humidity (RH) reduction rate in the base plate. The moisture diffusion depth of the base plate covered with geotextile and watered for 14 days is only 65 % of the base plate depth. To minimize shrinkage deformations, extending the water curing period is recommended. Additionally, the hydration rate of the base plate covered with plastic film is higher than those of the other two curing methods, resulting in greater temperature and humidity gradients, therefore, the construction process involving plastic film covering is not recommended.