Temperature Field Analysis And Temperature Control Method Of Concrete Structure In Construction Phase

Concrete Hydration heat will cause a sharp change of concrete internal temperature and make the difference of temperature between inside and outside of concrete increase. When the tensile stress caused by expansion is greater than allowable tensile stress, the structure appears cracks.After cracks appeared, its performance is widely different with the original properties of concrete, which seriously affects the long-term safety and durable operation of its structure. The cracks are mostly appeared in the early time so that it is important to study the causes of cracks and find ways to prevent the appearance of cracks.This paper first introduces the temperature load and thermophysical characteristics of concrete, then describes the differential equation of thermal conduction, the finite element method of temperature field, calculation principles of hydration heat and the definition of temperature gradient in the bridge design standards.Subsequently, this paper introduces the existing calculation method of actual temperature rise and then proposes a formula to estimate the hydration heat of concrete based on the principle of heat conservation. A calculation example shows that the results of the new formula are basically consistent with those of finite element software except partial differences. These differences may be due to the differences of calculation theory and the unclear relationship between heat transfer coefficient and thermal conductivity.Again, by controlling the factors of concrete hydration of thin-walled structures, it can conclude that with the reduction of thickness, with the decreasing of casting temperature, and with the decreasing of the heat transfer coefficient, the differences between inside and outside part of structure as well as the thermal stress and the possibility of cracks will highly decrease. Elevating ambient temperature can play a role in reducing the temperature difference, but the effect is limited.Then it introduces the effect of pipe cooling on the mass concrete by controlling the parameters of pipes cooling system.With the thickness of the concrete structure increasing, pipe cooling will be used as an effective method to control the temperature of mass concrete.The final part of the paper states the reasons of appearance of cracks in mass concrete, and crack control method in the construction process, such as designing a reasonable structure, optimizing concrete mixed proportion, controlling the construction temperature, strengthening construction management.