The Research Of Hydration Heat Temperature Effect And Crack Control On The Zero Blocks Concrete Of Long-span PC Continuous Box Girder Bridge

In recent years, the cantilever construction method has been widely adopted in large-span continuous prestressed concrete box-girder bridges. The pier segments in this type bridges usually have several common attribute of large dimensions, complicated shapes and high strength concrete. Therefore, the cast-in-situ pier segments prone to crack due to significant temperature difference between the box interior and exterior produced by hydration reactions in the construction process. Since the pier segments are the vital components in the cantilever constructed large-span bridges, temperature effects due to concrete hydration reactions and crack control for the pier segment of long-span PC continuous box-girder bridge warrant more extensive study.In this paper, the pier segments are studied by experimental measurements and finite element(FE) analysis with the support project, the main bridge of the Lao Zhang He Bridge on Hebei province. Based on a precise FE model validated by the measured temperature records, the temperature fields and effects resulting from hydration reactions in pier segments of the large-span PC continuous box-girder bridges are studied when the segments are constructed ordinarily or with cooling pipes. In this vein, some measures to prevent crack in pier segments are proposed. The specific research contents are as follows:(1) Use the temperature history data of key thermal points in several sections of the pier segments to analyze the temperature fields and effects of the pier segments due to hydration reactions during the casting process. On this basis, the temperature gradients of the box girder are fitted.(2) A comparison conducted to cross-check the experimental measurements and numerical results of the temperature data in the box girder to verify the validation of the FE model for hydration reactions analysis. Then, the approximate locations of the temperature cracks are estimated.(3) Use the software, the MIDAS FEA, to simulate the casting process of the pier segment, which is constructed by ordinary method without any cooling approach or special method with cooling pipes. Compare the temperature distribution and stress in the pier segment due to hydration reactions in these two scenarios. Finally, some reasonable crack control measures are proposed.(4) From the point of views of design and construction, crack control measures are proposed for the pier segment in large-span PC continuous box-girder bridges.