Study On Temperature Control And Crack Prevention Of Concrete Of Elbow Inlet Passage Of Large Pumping Station

The elbow inlet passage of large pumping station is both mass concrete structure and complicated structure.Cracks always appears in theses areas during construction period.It will require high cost of cracks treatment and endanger the safety of pumping station.Therefore,to research and put forward optimized temperature control measures is greatly engineeringly significant.But the existing research on remperature control of mass concrete can not be applied to elbow inlet passage directly for its structure complexity.Consequently,it is necessary to investigate the temperature control and cracks prevention of concrete of elbow inlet passage.Based on the project,this paper carried out the 3-D simulation of concrete of elbow inlet passage to analysis the value and variation laws of temperature and thermal stress by using ANSYS software.Then,the optimized temperature control mearures was put forward and validated through temperature monitoring.Considering the problems of inlet passage of Fankou second pumping station and Yaokou pumping station pouring in summer and winter respectively,the variation laws of temperature and thermal stress of concrete is researched.Based on the results of variation laws,the temperature control and cracks prevention mearsure is put forward.Then the actual temperature control measures in site are analyzed basing on the results of temperature monitoring.Based on the analysis results,suggestions for temperature control during construction period are put forward.According to the characteristics of Fankou second pumping station pouring in summer,sensitivity analysis is made on pouring temperature,heat preservation measures and parameters of water cooling.It is concluded that lowering pouring temperature,heat preservation in summer and water cooling can reduce the stress of concrete in the early pouring period,increase the minimum coefficients of safety for crack prevention and the duration of water cooling should not be too long.According to the characteristics of Yaokou pumping station pouring in winter,the sensitivity analysis of heat preservation with or without water and the duration of heat preservation in winter is carried out.The conclusion is drawn that the effect of temperature control and crack prevention of heat preservation is better than that of water cooling;the duration of surface heat preservation in winter should not be too short,and the measures of hanging curtain heat preservation at the inlet and outlet of inlet passage should last for the whole winter.Considering the different seasons,it is suggested that surface heat preservation before concrete pouring in cold season and the internal surface heat preservation when it become winter of concrete poured in other seasons should be done well in construction.In adition,it is really essential to do well surface and internal surface heat preservation of elbow-shaped intake channel poured in autumn.According to the analysis of the effect of adiabatic temperature rise on temperature and thermal stress of concrete,reducing the adiabatic temperature rise and temperature rise rate has a positive effect on temperature control and crack prevention.Therefore,it is suggested that the process of adiabatic temperature rise should be controlled from raw materials and pouring temperature.In order to avoid the occurrence of temperature cracks,the adiabatic temperature rise process can be controlled by optimizing cement varieties,reducing cement dosage,adding concrete admixtures reasonably and strictly controlling pouring temperature during construction.