Hydration temperature rise and thermal stresses induced in segment-on-pier of prestressed concrete box girder bridge

The heat generation from chemical reactions of hardening concrete causes temperature rise and thermal expansion. When the concrete temperature eventually cools down to the ambient, thermal contraction would result. If the tendency of volume change and associated thermal movement are restrained, thermal stresses would be induced and this would lead to early thermal cracking. The issue of thermal cracking should be duly considered in mass concrete construction. Regarding concrete bridge construction, the piles, pile caps, bridge piers, crosshead girders, and bridge diaphragms are typical examples of mass concrete elements. A bridge project in real-life is selected for study in this paper, with focus on the segment-on-pier accommodating the diaphragm of prestressed concrete girder deck. The segment was instrumented to measure its actual early age temperature rise on site. Finite element simulation and analysis was conducted to evaluate the time variations of temperature distributions and thermal stresses induced in the bridge segment. The risk of thermal cracking can be indicated by the measurement and analysis results. The techniques employed in this study are useful for planning of temperature control measures in similar projects.