Early-Age Hydration Heat in Railway 60-Meter Precast Box Girders: Experimental Study and Experimental Simulation

Large precast concrete box girders are susceptible to cracking due to excessive temperature differentials induced by early-age hydration heat, compromising structural reliability and durability. Investigating the early-age hydration heat in large precast box girders and proposing corresponding temperature control measures based on influencing factor analysis is therefore essential. The present research employs field testing and numerical simulation of a 60 m precast railway box girder to develop a UMATHT subroutine and establish a refined finite element model incorporating temperature-dependent material properties and hydration degree. Results demonstrate that the early-age temperature field exhibits an initial rise followed by a decline. Pouring temperature exhibits a positive correlation with both peak temperature and maximum temperature differential; a 5 °C increase in pouring temperature elevates the temperature differential by nearly 1.8 °C. Cement content significantly affects peak temperature, with an average increase of approximately 5.4 °C per additional 50 kg/m3 of cement. Ambient wind speed exerts a greater influence on temperature evolution during the cooling phase than the heating phase. Increased ambient wind speed reduces the peak sectional temperature while concurrently increasing the surface temperature gradient on the windward side of the girder.