Study On Creep Property Evolution Law Of Concrete Under Industrial High-temperature And Constant Humidity Steam Curing Environment

Industrial intelligent flow production,which takes combined intelligent mold,integrated concrete mixing,feeding,distribution and vibration discharge,steam curing under the intelligent control of high temperature and constant humidity,and early tension of prestress as its core technologies,is a new manufacturing process of concrete bridge under the background of new construction industrialization.Steam curing with high temperature and constant humidity is the key link.The steam curing of high temperature and constant humidity in industrial production accelerates the hydration reaction process of concrete,changes the composition proportion of hydration products and the distribution of microstructure,and affects the early deformation and long-term creep performance of concrete.Based on 30 m segment prefabricated T-beam,this paper analyzed the comprehensive temperature field inside concrete through full-size field test,optimized the temperature and humidity control parameters of industrial steam curing production process,and put forward the steam curing production process parameters that meet the industrial flow rhythm.On this basis,the influence of curing method and loading age on concrete creep deformation was analyzed from the micro and macro levels by combining experiment and theory.Finally,based on rheology theory,a creep prediction model suitable for industrial production of concrete was proposed to evaluate the longterm performance of concrete.The main research contents and conclusions are as follows:(1)Through the temperature field and temperature gradient tracking test of concrete,the reasonable production process and curing parameters of industrial high temperature and constant humidity steam curing were determined,that is,each production line was equipped with two concrete steam curing rooms,each room curing 5h,10 h in total.The first curing room heats up to 50℃ according to 10℃/h and 3h,and enters the next curing room at the end of constant temperature until 5h.The second curing room maintains a constant temperature of 50℃,0.5h,then the temperature is lowered to 30℃ after 2h at10℃/h.Stop steam input,and cool down naturally for 2.5h until the end of steaming.At the same time,it meets the requirement that the strength of concrete exceeds 50% of the design strength after the end of steaming and demoulding.(2)Through SEM scanning electron microscope and axial compression creep test,the influences of curing method and loading age on creep deformation of concrete were analyzed from the micro and macro levels.The results show that: the porosity of concrete increases,the pore size coarsens,and cracks exist in the interfacial transition zone(ITZ)of concrete.The creep deformation of concrete decreases with the increase of loading age,and increases with the increase of load holding time.The change is faster in the early stage of load holding,and gradually becomes stable with the increase of load holding time.Under the same load holding time,the creep deformation of concrete under high temperature and constant humidity steam curing is larger than that under standard curing.However,when the loading age is same,the creep deformation of concrete under high temperature and constant humidity steam curing is less than that under standard curing condition.(3)The viscous cement slurry is the main reason affecting the creep deformation of concrete.A concrete creep model based on rheology theory was proposed from the micro level,namely,Burgers modified model.On this basis,combined with the long-term creep deformation law of concrete obtained from axial compression creep test,a concrete creep prediction model suitable for the industrial production is proposed.