Research On The Cooperative Internal And External Curing Of Structural Concrete In Arid And Windy Areas

Structural concrete pouring on site in arid and windy areas faces some problems,such as high risk of early cracking and poor late durability.For example,the cracks caused by low humidity and windiness occurred in the early stage of curing of the concrete for structures such as bridges and monolithic track beds of the track systems in LanzhouXinjiang Railways,which seriously affects the safety and durability of the structures.In arid and windy environments,the water loss rate of traditional sprinkling maintenance is relatively fast,the film curing package is not tight,the strong wind blows and breaks,the curing of high pier is difficult to operate,and the maintenance effect is not good.Therefore,an internal and external cooperative maintenance technology was proposed in this paper.First,the adsorption and desorption laws of internal curing materials of zeolite powder were studied.The theoretical model of internal relative humidity of internal curing concrete was established,and the influences of temperature and wind speed on its internal relative humidity were analyzed.Then,the influence of internal and external cooperative curing technology on concrete strength and crack resistance was studied at the arid and windy environments.Finally,the mechanism of internal and external cooperative maintenance was analyzed.The research results can provide references for the construction of Sichuan-Tibet railway and other engineering practices.The main work and conclusions of this paper are as follows:(1)The adsorption and desorption laws of zeolite powder with three particle sizes of250,180,and 75μm at different temperatures of 10°C,20°C and 30°C and environmental relative humidities of 100%,90%,80% and 70% were studied.And a theoretical model for adsorption and desorption of zeolite powder was established.With the decrease of the particle size of zeolite powder,the saturated water absorption rate and water release rate increased.With the increase of the temperature,the adhesion between zeolite powders and water of zeolite powders with different particle sizes decreased,and the amounts of adsorption and desorption gradually decreased.With the decrease of the relative humidity,the amounts of desorption water of zeolite powders with different particle sizes gradually increased under the action of humidity difference.The calculated values for the amounts of saturated water absorption of zeolite powder and the amounts of desorption water at different humidities agreed well with the experimental results.(2)The variation laws of internal relative humidities of different concretes under different curing environments(temperature and wind speed)were studied,and the theoretical model of internal relative humidity of internal curing concrete was established.The variation of internal relative humidity of concrete with time could be divided into two stages: humidity saturation period and humidity decline period.Under different conditions,the closer the distance to the dry surface was,the faster the rate of descent in internal relative humidity in concrete was.Under the condition with wind speed of 5m/s,the internal and external cooperative curing effect was the best,and the relative humidity in the concrete at the age of 28 d was 19% higher than that of ordinary concrete.The experimental values of the internal relative humidity were in good agreement with those calculated by the theoretical model.The internal relative humidity theory model was used to analyze the variation law of the internal relative humidity of concrete with different temperature and wind speed.When the wind speed or the temperature increased,the saturation period of the internal relative humidity shortened,and the decline rate of the internal relative humidity decreased more quickly.(3)The influence of arid and windy environment on concrete performance was studied,and the influence mechanism of internal and external cooperative curing was analyzed.The results showed that the strength of internal curing concrete increased,and the early expansion and late shrinkage of concrete were reduced,and the crack resistance of concrete was improved by using internal and external cooperative curing technology in arid and windy environments.Based on the characteristics of zeolite powder and the composition of curing agent,the influence mechanism of internal and external cooperative curing on concrete performance was analyzed.