Research On Hydration Thermal Effect And Temperature Control Measures Of Mass Concrete Pile Cap

With the rapid development of China's economy,the number of long-span bridges under construction and ready for construction is increasing.With the increasing number of long-span bridges,mass concrete structure is an ideal load-bearing structure for large-span bridges because of its good load-bearing performance and simple construction process.Generally,large-span bridges use mass concrete caps as bridge foundation structures.Problems are arising with the use of mass concrete caps.Thermal cracks of mass concrete caps caused by excessive internal surface temperature difference of mass concrete caps have more and more serious impact on their safety,reliability and durability.Under the action of hydration heat of cement,construction environment,thermal insulation measures and internal pipe cooling system,mass concrete caps generate complex temperature field in their structures,which results in the difficulty of controlling internal surface temperature difference,maximum adiabatic temperature rise and surface temperature.In this paper,the Bridge(a continuous rigid bridge with variable cross-section and pre-stressed concrete of which the main span is 92.75m+6×170m+92.75m)is taken as the research support project.It guides the construction through the pre-finite element simulation analysis.In view of the implementation of temperature monitoring of the main pier cap,and comparing with the calculated value of finite element software simulation analysis,the controlling factors affecting the temperature field of mass concrete cap are found out and analyzed.Combining with various documents,data and codes,the calculation methods of adiabatic temperature rise,specific heat capacity and thermal conductivity of concrete are systematically summarized.The system also guides the construction with the construction site environment of main pier cap and the constructing finite element model of main pier cap.After monitoring the hydration heat state of the main pier cap,the finite element model is modified.By comparing the theoretical calculation value of the modified finite element model with the measured value,the accuracy of the finite element software Midas Civil is verified,and the controlling factors affecting the temperature field of the main pier cap are found.By means of the finite element software Midas Civil and Midas FEA,the controlling factors(The temperature of concrete in the mound,the adiabatic temperature rise function in the finite element software,the thermal conductivity coefficient,the convection coefficient of concrete surface,the ambient temperature and the parameters of pipe cooling system,etc.)affecting the temperature field of the main pier cap are numerically analyzed,and the influence law and degree of the controlling factors are found out.