Study On The Expansion Deformation Mechanism And The Control Technology Of Steam-cured Concrete

Steam-cured concrete prefabricated components are widely used in the infrastructure construction of high-speed railway in China,which effectively speeds up the construction progress of high-speed railway and has produced significant economic value and social effects.Steam-cured concrete prefabricated components are in great demand,but they also show defects such as durability decline and embrittlement in the actual service process,which is related to the thermal damage caused by the moisture and heat effect of steam on concrete.At present,scholars at home and abroad have carried out more researches on the hydration kinetics,dynamic and static mechanical properties,phase evolution,and multi-scale structural characteristics of steam-cured concrete;however,there is a lack of systematic research on the accurate characterization and generation mechanism of expansion deformation of steam-cured concrete.Based on the above,this paper takes the typical steam-cured concrete of prefabricated components of high-speed railway as the research object,carries out relevant research work through theoretical analysis and indoor tests,and obtains the following innovative achievements:(i)An integrated test device for measuring the stress-strain of concrete under restraint during the hydrothermal curing environment is developed.The variation principle of internal stress of concrete with different initial structural strength under restraint during steam curing process is analyzed,the internal stress evolution mechanism of steam-cured concrete is clarified,and the control principle of internal stress of steam-cured concrete is also put forward.(ii)An integrated test device for dynamic deformation of cement-based materials without restraint during thermal curing process is developed.The expansion deformation evolution characteristics of concrete with different initial structural strength without restraint during steam curing are analyzed,the formation mechanism of expansion deformation of steam-cured concrete is briefly described,the expansion deformation model of steamcured concrete is established based on the thermal expansion effect of water vapor and shrinkage deformation,and the internal relationship between internal stress and expansion deformation of steam-cured concrete is also clarified.(iii)The control principle of expansion deformation of steam-cured concrete is put forward based on the initial free water content,compactness,initial structural strength and maximum curing temperature of the mixture.The expansion deformation control technology based on the optimization of cementitious components and curing system is also proposed,and the correlation between initial structural strength and expansion deformation is clarified.(iv)The long-term performance of steam-cured concrete is contrastively studied,which further verifies the rationality and applicability of the optimization of both the cementitious components and the curing system.