Research On Early Temperature Effect Of Large Volume Concrete

The increase of concrete structure size result in the sudden increase of concrete consumption,which leads to a series of problems about the heat effect of concrete hydration.Continuous rigid frame bridges are widely used in high-speed railway,and its concrete strength grade is higher and higher.Compared with ordinary Portland cement,hydration heat temperature is slower in center cooling rate,and it takes longer time to reach the expected temperature value.On the other hand,the rate of heat production is quite opposite,and the heat accumulated inside the structure is even more difficult to emit in time,and the internal and external temperature difference is extremely easy to exceed 25 ? when the surface concrete does not take effective insulation measures.The surface of the structure will produce tensile force even greater than the allowable tensile strength of concrete.In the existing research data,most of the hydration heat problems of cap concrete are concentrated on ordinary concrete,and the hydration heat problem of high-strength concrete with a thickness of 2m has changed differently.It is necessary to study the temperature field and stress field of high strength concrete members,which can not be guided by the rules of hydration heat temperature field and stress field of ordinary concrete,so it is necessary to study the rules of temperature field and stress field of high strength concrete members.In this paper,a continuous rigid frame-arch composite bridge is selected as the project background,and 552 main pier cap is chosen as the research object.The temperature field and stress field of high strength concrete hydration are studied.The main research work is as follows:(1)Before the construction,four construction plans were preliminarily drawn up,and the heat of hydration of the platform under construction was studied by using finite element software MIDAS/Civil.The distribution patterns of the temperature and stress fields of the platform under different construction plans were analyzed and compared.to provide a scientific and reasonable temperature control program which guide the construction process and avoid the hazards of thermal cracks in the heat of mass concrete.(2)According to the characteristics of the concrete structure of the bearing platform,a reasonable monitoring program for the temperature of hydration heat was developed,we determined the scheme about scientific and comprehensive temperature measurement points of the hydration heat of the concrete over entire period.Analyzing and summarizing the measured temperature data of the bearing platform to obtain the temperature change rule of the base platform.(3)Using the three-dimensional finite element software MIDAS/Civil,the finite element simulation of the entire hydration heat temperature field was performed according to the actual cooling water pipe layout,water flow conditions,boundary conditions,and actual construction process.The thermal parameters of the high-strength concrete were optimized,so that the simulation results of the three-dimensional hydration heat temperature field after considering the effect of the cooling water pipe were more in line with the actual situation.By comparing the measured temperature field with the calculated temperature field,it lay the foundation for the numerical test.(4)According to the construction conditions of the platform on the site,the impact of mold temperature,ambient temperature,and cooling water pipe parameters on the temperature of the bearing platform was studied.We determined the temperature control improvement measures for mass concrete.Aiming at the problem of low thermal insulation effect of the top reservoir,new optimization measures were proposed and verified by numerical analysis.This measure could reduce the temperature difference between the inside and outside of the concrete to decrease the cap of temperature gradient from the top surface to the center and possibility of cracks at the early stage.