Mitigating Hydration Heat Cracking in Massive Pile Caps: An Integrated Approach with Concrete Lifting, Pipe Cooling, and UHPC Overlay

To mitigate early-age thermal cracking in mass concrete pile caps for sea-crossing bridge, this study proposes an integrated approach combining concrete lifting, pipe cooling, and an ultrahigh-performance concrete (UHPC) permanent overlay. The approach was investigated using a thermomechanical finite-element model (FEM) validated with field monitoring data from a real bridge project. Parametric studies quantified the effects of lift thickness (1–6 m), pipe spacing (0.5–3.0 m), and UHPC thickness (5–80 cm) through FEM. Results demonstrate that reducing lift thickness and pipe spacing significantly decreases the maximum temperature rise, core-surface temperature difference, and maximum principal stress, with average reduction rates of −5.2°C/m and −8.1°C/m for temperature rise, respectively. Incorporating a UHPC overlay reduces concrete tensile stress primarily through its restraining effect (average contribution of −27.77%), secondarily via insulation. While the three measures show comparable effectiveness, with stress reduction rates of −0.88, −1.19, and −0.04 MPa/cm, none could eliminate cracking risk within practical limits alone. The integrated scheme reduces the cracking index (σ1/ft) below 0.75, providing an effective solution for early-age crack control in mass concrete under demanding environments.