Study On Temperature Control Of Mass Concrete Of Pile Cap Of Cross-sea Bridge

In recent years,with the rapid development of China’s economy,a large number of seacrossing bridges are being planned and constructed,and the application of mass concrete in seacrossing bridges has become more widespread.Due to the working environment of sea water,sea breeze and high humidity,sea-crossing bridge has higher requirements on the crack control and durability of concrete.Supported by the National Natural Science Foundation of China(51408218),relying on Gangbei Bridge in Wanning,Hainan(prestressed conc-rete continuous box girder low-pylon cable-stayed Bridge;the span of the bridge is 80 +138 +80 = 298m)and southward navigation opening bridge of the main channel of Zhoushan Port in Ningbo,Zhejiang(a double-tower cable-stayed bridge with full steel box girder and double cable planes;the span of the bridge is 74+106+390+106+74 =750m),a temperature control study was carried out on the mass concrete of pile cap of the cross-sea bridge.The main research contents and conclusions are as follows:(1)The cooling system design and temperature field of hydration heat measurement were carried out for the pile cap of the Gangbei Bridge and the southward navigation opening bridge of the main channel of Zhoushan Port,the temperature control effect is good,and didn’t appear the thermal crack.(2)Based on the measured results,a simulation model was established to simulate the hydration heat process of the mass concrete pile cap.On the basis of the good agreement between the calculated temperature field and measured values,the parameters such as concrete mix proportion,casting temperature,environmental temperature,cooling method and maintenance measures under extreme environmental were simulated and analyzed.(3)The design of the marine mix ratio of mass concrete should meet the requirements of low hydration heat,good construction performance and excellent durability.The compounding technology is preferentially used,and the retarder is appropriately added to delay the time of peak temperature and reduce peak temperature.The pump temperature should be strictly controlled on site according to the construction season.In terms of the situation analyzed,when the casting temperature decreased 10 ℃,the peak and the temperature difference between the center would respectively decrease 8.33 ℃ and 4.26℃.(4)The marine environment is faced with environmental extremes such as drastic temperature changes and strong winds,it is necessary to prepare a plan for the impact of environmental extremes such as sudden cooling and strong winds on marine mix ratio of mass concrete.As far as the analysis results are concerned,the environmental temperature and environmental wind speed mainly affect the surface temperature.When the environmental temperature decreased 10℃,the core temperature did not change,the surface temperature decreased 9.05℃,and the temperature difference between the center exceeded limiting value.(5)The cooling mode is very important for the internal cooling of the pile cap.In the process of temperature control,the flow rate and temperature of the cooling pipe should be strictly controlled.The cooling efficiency would be reduced when the flow rate of the cooling pipe is higher than a certain value;the water temperature mainly affects the cooling rate,and the appropriate cooling water temperature should be selected during the cooling stage.During this period,the cooling water flow and temperature should be adjusted dynamically according to the test results.(6)Maintenance should be strengthened during the construction of mass concrete,and the removal of shuttering time should be strictly controlled.As far as the analysis results,geotextiles and colored strips have a windproof and thermal insulation effect,and they should be covered and insulated before the peak temperature is reached.If extreme low temperature weather occurs during construction,quilts or other insulation materials should be used to cover the insulation.It is recommended that the removal of shuttering time of marine mass concrete pile cap should be no less than 7 days under normal weather,and it should be properly delayed when under the strong wind.