Simulation Of Temperature And Humidity Field In Concrete Under Cyclical Temperature And Humidity

Durability of concrete materials and structure is strongly influenced by cracking inducedfrom the poor volume stability. The cracking caused by shrinkage of concrete would remarkablyincrease the permeability and make the deterioration of carbonation, chemical attack andreinforcement corrosion easier to occur, and thus heavily deteriorate the durability and servicelife of concrete structure. In real engineering structure, the deformation and crackingperformance of concrete results from the coupling effect of environmental temperate, humidityand structural loads. It is very important to simulation of temperature and humidity field inconcrete under cyclical temperature and humidity.Focusing on simulation of temperature and humidity field in concrete under cyclicaltemperature and humidity, composite materials mechanics and homogenization ofmeso-mechanics method were used to investigate the mechanism, model and numericalsimulation approach concerned at different scale of size. The research content involving themechanism and modeling of moisture and heat transfer in hardened cement paste,meso-mechaincal deformation mechanism of concrete, numerical simulation of hygro-thermaldeformation of concrete specimen. According to the typical pore size and distribution ofhardened cement paste, the influence of Knudsen diffusion must be considered when analyze themoisture transfer mechanism. Then the mechanism and transfer model of moisture transferincluding the effect of Knudsen diffusion was proposed. The deformation mechanism of concreteshould be investigated according to the composite materials mechanics based on the three phasesof hardened cement paste-interface transition zone-aggregates, stress-strain relationship ofhardened cement paste. The basic physical and mechanical parameters of concrete should bededuced according to homogenization method under the assumption that cement paste andaggregates are homogeneous material. The discipline and definition, theoretical formulation andinversion method of Hygroscopic Expansion Coefficient were proposed, deduced and conducted.Based on the transfer mechanism and model of porous hardened cement paste, the numericalsimulation method using COMSOL Multiphysics software of hygro-thermal deformation were analyzed and verified through some case analysis. The variation characteristics of environmentaltemperature and humidity, the deformation cracking mechanism of concrete in service life underhygro-thermo-mechanical coupling effect were preliminary analyzed. And the potentialnumerical simulation approach and softwares were also discussed in the paper.It can be concluded based on the relative research results as follows:(1)It could be morereasonable to consider Knudsen diffusion when analyzes the moisture transfer mechanism ofhardened cement paste;(2) The proposed Hygroscopic Expansion Coefficient and itsdetermination form theoretical and inverse method were reasonable and applicable;(3) Thenumerical simulation of hygro-thermal deformation of concrete based on the heat and moisturetransfer mechanism in porous media is reasonable and useful for numerical simulation ofconcrete deformation;(4) The damage similar to fatigue will occur in structural concrete undercyclic environmental temperature and humidity and service loads;(5) The COMSOLMultiphysics software suitable for multi-physics fields analysis is also beneficial to thenumerical simulation of concrete deformation cracking performance considering the couplinghygro-thermo-mechanical effect;(6) Quite a few problems concerning the HygroscopicExpansion Coefficient, hygro-thermo-mechanical cracking mechanism of concrete should besolved after further researches in future.