Study On Hydration Heat Control During Construction Of Large Volume Concrete For Pile Caps

In the construction of long span bridges,the volume of the pile cap foundation is usually large,and the casting process of the pile cap belongs to the mass concrete construction.During the construction of mass concrete,due to the heat generated by cement hydration,the temperature of the concrete inside is raised,the cracks are produced during the plastic shrinkage and hardening process.The temperature and the temperature stress in the structure are complex,which causes the shrinkage of concrete unevenly.The prevention of temperature cracks in mass concrete is mainly taken into consideration in two aspects.One is to reduce the internal and external temperature difference of concrete directly by means of heat transfer,such as internal heat dissipation and external heat preservation,mainly including using ice water to reduce the temperature of the entry mold by mixing concrete and concrete,and reducing the internal temperature of concrete by cooling tube cooling method.Surface coverage and other measures reduce the temperature difference inside and outside the concrete;the other is to optimize the types of raw materials,through the reasonable mix ratio design,the optimization of raw materials,and other measures to improve the performance of cement by adding admixtures,reduce the amount of cement and water,reduce the heat of hydration and so on,reduce the self heating of cement.The main contents of this paper are as follows:(1)The hydration heat release process of mass concrete is analyzed,and the principle of hydration heat release of concrete is discussed.(2)Based on the analysis of the thermodynamics theory of concrete and the influence factors of the temperature stress in the pouring process,the influence of the concrete material on the hydrated heat release is deeply studied,and the finite element model is established to explore the factors affecting the temperature stress in the concrete construction process.(3)In this paper,through the establishment of the model,the arrangement of cold pipe,the spacing of cold pipe,and the water volume of the cold pipe are analyzed and compared.It shows that the arrangement and spacing of the cold pipe have significant influence on the cooling effect,while the other factors have little effect on the cooling effect of the cold pipe.(4)Combining theory with finite element analysis,the cooling method of case engineering is analyzed.Through the rational arrangement of the cold pipe arrangement,the concrete temperature in the construction process is effectively controlled,and the temperature field and the change law of the temperature stress in the first pouring of the mass concrete are analyzed.