The Analysis Of The Cold Shock Phenomenon Caused By The Low Pouring Temperature Of Concrete During The High Temperature Season And The Temperature Control Measures

Due to the requirements of the construction schedule,concrete dams can not avoid to be poured in high temperature season.Some concrete dams are located in the regions where are very hot and have strong solar radiation in summer.The temperature of the concrete surface which can reach 40 ℃ under the condition of inadequate maintenance is greatly fluctuated by the influence of air temperature and solar radiation in this area.However,based on the requirements of the temperature control of the dam concrete,these dams often use the pre-cooling method to control the outlet temperature and the pouring temperature of the concrete at a lower temperature.Therefore,the newly entered concrete at a lower temperature will have a ‘cold shock’ effect on the old concrete with a very high surface temperature,resulting in greater tensile stress on the surface of the old concrete.When the cold shock stress is more than the tensile strength of the concrete at this time,the surface of the concrete has a large risk of cracking,which affects the quality of the bonding of the concrete layer,and even becomes the cause of the growing crack in the later period of the project.Therefore,we need to analyze this phenomenon and propose the targeted temperature control measures to avoid this phenomenon endangering the safety of engineerings.In this paper,based on the monitoring data of the cold shock test of the Xiluodu arch damc which caused by the concrete with a low pouring temperature,the temperature field of concrete was calculated by the numerical simulation.And the accuracy of the temperature field simulation model was verified by the measured temperature data.After confirming the high accuracy of the model,the temperature stress of concrete was calculated by taking the temperature as the load,and the tensile stress of concrete under the cold impact was checked whether it was overproof.Then,with the concrete tensile stress and the highest temperature not exceeding the standard,the reasonable pouring temperatures of the concrete and the reasonable maintenance measures of the working unit were feedback.Finally,the proposed temperature control measures were applied to the Baihetan dam.The cold tensile stress that whether taking the temperature control measures was compared through the simulation analysis.So the effectiveness of the research results in this paper was verified.,and the general temperature control measures were provided for similar projects to solve the cold shock problem of concrete with a low placing temperature.The results showed that the surface temperature of the 26 th block concrete decreased by 18.2 degrees in one day,which resulted in the cold tensile stress of 1.62 MPa on the surface when the concrete of the 16#27th block of Xiluodu dam pouring at a low temperature during the high temperature season.So the concrete faced a great risk of cracking because the cold tensile stress exceeded the current tensile strength of the concrete.Through the feedback analysis,it was found that the strength and temperature requirements of the concrete under the cold shock can be met by controlling the concrete pouring in a reasonable temperature range and running the water maintenance on the surface of the concrete.Then,the proposed water maintenance measure of the casting block surface was applied to the Baihetan project,and it was found that the cold tensile stress produced by the concrete pouring at a low temperature was reduced from 1.21 MPa to 0.34 MPa,which was far below the current tensile strength of the concrete.So the concrete won’t crack due to the cold shock.Therefore,the water maintenance of the casting block surface had a good effect on solving the cold shock cracking problem of the concrete which is pouring at low temperature.And it can be used as the first choice of temperature control measures to solve the cold shock cracking problem of the similar projects.