In order to investigate the influence of different steam curing conditions on the mechanical properties and hydration heat effect of 30 m box girder using C50 concrete,a steam curing test was conducted.The effects of two sets of parameters including constant temperature(40,45,50 ℃)and its duration(12,16,24 h),on the development of compressive strength and elastic modulus at ages of 2,3,7,and 28 d were discussed.Based on the results of the steam curing test,steam-curing parameters and a testing scheme for the girder were proposed.In the field test,the hydration heat temperature of the girder was monitored,and the mechanical properties of specimens cured along with the girder were tested.The rational feasibility of the curing scheme was thereby verified.A finite element model was established to analyze the temperature field during steam curing.The results show that the concrete compressive strength and the elastic modulus are positively correlated with both constant temperature and its duration while excessively high temperatures or prolonged durations may have adverse effects on the concrete strength at later stage.Based on the field test results,a constant temperature of 45℃ and a constant time duration of 16 h are suggested.Compressive strength and elastic modulus at early ages meet prestress tension requirements.To prevent cracking,the heating and cooling rates during the steam curing process shall be strictly controlled,and the temperature gradient within the girder during the early stage of concrete hydration heat process shall be appropriate.In summer,the temperature of the girder can be easily elevated through steaming while the cooling process is difficult.To promote a stable transition of concrete hydration heat temperature,the time distribution of each steam curing stage may be optimized through the implementation of preheating and precooling.
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