Study On Multi-field Coupling Characteristics And Crack Resistance Of Constraint Surface In Early Age Of Concrete

The wet joint provides convenience for engineering construction,and also provides guarantee for the anti-cracking of mass concrete with piecewise and laminated pouring.However,the shrinkage deformation of wet joint is affected by environment and surrounding constraints.For instance,the cracking problem of post-poured member and construction which includes the transverse and longitudinal wet joints of composite beam bridge deck,the wet joint of continous bridge erected as simple-supported beam,the wet joint in closure section of PC beam and the wet joint when casting mass cushion cap Concrete in section.Compared with the research on wet joint concrete crack in bridge during use,the cracking mechanism of early-age concrete in which significant changes about temperature,humidity and mechanical property have taken place is lack of research.Therefore,studying on the coupling and evolvement rule among temperature,humidity and stress in early-age concrete and figuring out the sensitive cracking time and area of early-age concrete in wet joint,and preventing the concrete cracking at early age have a significant practical engineering value.This thesis takes the temperature,humidity and stress of early age concrete as research object,relying on wet joints of canal bridge approach of Heng De highway and Ping Yin Yellow River Bridge of Qing Lan highway.Conducting in-depth research on hygro-thermal-mechanical coupling Characteristics of early age concrete and analyzes the evolution law and coupling Characteristics of concrete temperature,humidity and stress at early age under different constraint conditions by laboratory test,theoretical analysis,numerical simulation and In-situ test method.This article redivides the concrete variation stage at early age from the point of temperature and humidity variations and proposes the new constraint surface Anti-Crack measures.The main research conclusions are as follows:(1)An experimental study on deformation of early age concrete is carried out,which optimizes the existing concrete temperature and humidity monitoring methods,making the humidity monitoring device embedded into concrete immune to the construction process and improving the usability of the devices in pratcical projects.The developing law of concrete temperature,humidity and strain at early age is obtained in sealed and unsealed environment,which provides the experimental support for the building hygro-thermal and hygro-thermal-mechanical coupling model in later section.(2)Based on hydration kinetic model,equivalent age theory and heat transfer and humidity diffusion theory,the numerical model of temperature and humidity fields in early age concrete is built from the principle of temperature and humidity variation in early age concrete.Based on the established difference equations of temperature and humidity change by Grank-Nicholson method,procedural language programmed is used to stimulate the temperature,humidity fields and coupling effect,the validity of numerical model is testified by experiment data and the laws of the interaction between temperature fields and humidity fields of early age concrete are anyslized.(3)Based on multi-phase porous medium mechanics theory,mixture theory,temperature transfer and humidity diffusion law and constitutive relation of early age concrete,this paper takes temperature,humidity,deformation and hydration degreee as the major variables and builds a multi-parameter hygro-thermal-mechanical coupling model under consideration of the early age concrete characteristic and external constraints.PEDs and corresponding physical modules are used to implement the finite stimulation.(4)Taking the wet joint of continous bridge erected as simple-supported beam as researh object,this paper optimizes the selection of measuring devices,measuring point position,the arrangement of measuring cycles,working condition selection and external disturbance and conducts the wet joint in situ experiment.Using the previously established hygro-thermal-mechanical coupling model,the evolution law of temperature,humidity and stress fields of confined concrete at early age is analyzed,the analysis of the cracking sensitive property of constrained conponents is also carried out in this paper,on this basis,the early age stage of concrete is refined and divided.(5)The research of anti-crack material on constraint surface between wet joint concrete and adjacent members is conducted.From the point of reinforcing concrete interface bonding property,the cement paste interface agent is modified by adding molecular polymer and mineral powder.By a series of tests,including,mixture ratio test of polymer interface agent,Flexural strength test,compressive strength test,tensile splitting strength test,Splitting tensile and bond performance test in constraint surface,this paper analyzes the mechanical and bonding properties of the new interface agent and builds a model of concrete interface bond which includes three areas and layers.