Investigations of the Temperature Field and Cracking Risk in Early Age Massive Concrete in the # 0 Segment of a Box Girder Bridge

Massive high-strength concrete is often used for the # 0 segment of continuous box girders in modern large-span bridges. Thus, the release of substantial hydration heat results in thermal cracking during construction, which greatly affects bridge safety and durability. To predict the risk of structural cracking, it is important to clarify the distribution of the temperature gradient associated with the hydration heat in the # 0 segment and develop an accurate and simple method for calculations to assess of cracking. In this study, based on an actual bridge project, the temperature variation of the # 0 segment caused by hydration heat were measured, and the temperature distribution and development were investigated. The finite element method (FEM) was utilized to simulate the temperature field of the # 0 segment. Three thermodynamic methods for the assessment of cracking were compared and analyzed by practical calculations, and the influence of different parameters on the cracking risk was investigated. Measurements showed that the temperature field of the # 0 segment had a skewed unimodal normal distribution in time and a U-shaped distribution of low and high temperatures in outer and inner positions, respectively. The temperature distributions associated with the hydration heat were discontinuous in time for the root section and obeyed different but correlated Gaussian functions along the width of different pouring layers of the intermediate crossbeam at the # 0 segment. Additionally, the results of the FEM simulation were very consistent with the measurements, which verified the accuracy of the FEM simulation. The cracking assessment methods in EC2 and GB 50496 were used to exactly evaluate the cracking of massive concrete structures. On the basis of the results of the study, it was recommended to reduce casting temperature, delay removal of formwork and control curing temperature above 15°C to curb cracking.