Investigations of the hydration heat of large-volume precast concrete bent caps using layered pouring and a new temperature control measure

Massive high-strength concrete generates significant hydration heat during casting, which indirectly influences the risk of structural cracking by affecting the internal temperature gradient distribution. This paper investigated the effect of layered pouring methods on internal temperature gradients in massive concrete using the precast bent caps of a Shanghai bridge project as a case study. The temperature-time development patterns of each poured layer were studied through three sets of physical experiments. Temperature gradient distribution functions were established to specify the spatial temperature distribution trends of each layer. The interconnectedness between the spatial temperature distributions of adjacent poured layers was explored based on the established distribution functions. Targeted anticracking suggestions for layered poured concrete were provided based on these correlations. Additionally, a novel temperature control measure for managing hydration heat was proposed. The feasibility of this measure was verified through practical experiments. Moreover, corresponding finite element models were established to investigate the influence of parameters such as structural lead, outer wall pipe radius, and cooling water flow rate on the internal temperature field of concrete. The hydration heat-time patterns of the poured layers all showed a skewed single-peak distribution. The hydration heat of odd- and even-numbered layers exhibited different Gaussian distribution patterns in the lateral direction; the correlation between the spatial temperature distributions of adjacent layers could be quantified by the ratio of the standardized variance of the Gaussian distribution function of temperature for each corresponding layer. Implementing temperature control measures at specific reasonable positions and using a natural logarithmic function to calculate the design limits of structural dimensions could effectively prevent structural cracking. The newly proposed hydration heat control measure improved the temperature gradient distribution within the concrete. Reducing the structural lead, increasing the outer wall pipe radius, and increasing the cooling water flow rate all resulted in a decrease in the peak temperature inside the concrete. Finally, a structural lead of 0.4 was recommended for actual construction projects, for which the outer wall pipe radius should not exceed 30 mm.