The Study Of Young’s Modulus Trans-scale Model On Concrete Transition Zone Based On Non-uniform Hydration

The concrete constitutive relation is the foundation of various concrete studies,including structure design,durability and reliability,and engineering optimization.A more objective and accurate concrete constitutive relation would strongly accelerate the development of relevant studies.Concrete is currently treated as a three-phase composite of aggregate,mortar and transition zone.In all the three phases,as the product of local specific hydration,transition zone affects the concrete macro-behavior significantly.Young’s modulus of transition zone is the key factor of the concrete constitutive relation,however,in current study on transition zone,specific hydration and gradient properties have not been associated quantitatively,the Young’s modulus’non-uniformity has not been taken into sufficient account in current concrete model.The investigation on hydration and Young’s modulus of transition zone can provide essential theory,in order to help to establish a more objective and accurate concrete constitute relation.In this paper,the permeability of packed cement grains was studied,a non-uniform hydration model was established.Based on the calculated porosity distribution on transition zone,the trans-scale Young’s modulus model of transition zone was constructed.In addition,the microcosmic constitutive concrete relation was developed,the uniaxial mechanical behavior of concrete was simulated.The thesis is organized as follows:（1）Interrelation among cement particle size-distribution,accumulation and permeability was studied.Based on classical seepage theory,2-dimensional fractal spectrum was introduced to show the size-distribution of cement particle.The particle-cluster was constructed to show the correlation of particle accumulation and pore.Finally,the permeability model of packed cement particle material was developed.The accuracy of suggested model in this thesis was verified by comparison with experimental data.The content of particles with diameter less than 5mm is negatively correlated with equivalent seepage pore size,the lower size limit of particles in cluster was decided by the adoption of minimum particle size.（2）Hydration model of transition zone was established,with respect to pore-permeation coupling effect.Based on HYMOSTRUC theory,the pore-permeation coupling effect was introduced,non-uniform hydration model suitable for transition zone was developed.The interaction between pore feature and seepage flow is estimated by pore-permeation coupling effect quantitively,non-uniform water distribution,fractal and non-fractal feature of pores were both taken into consideration.Verification with test data shows that when water-cement ratio is higher（ω₀=0.5,0.4）and slag content is lower than30%,the accuracy of proposed model is improved.Calculation based on non-fractal pore feature is more conservative than that of fractal pore feature.When slag content is higher than 30%,the accuracy of proposed model reduces with slag content is increased.（3）The description parametric and statistical on mesoscopic pore morphology of transition zone was proposed.According to mesoscopic pore morphology in transition zone,representative volume element（RVE）with pore inclusion is established for components.The morphology of pore inclusion is depicted parametrically;morphology parameter distribution functions are constructed statistically.This part of work provides theoretical support for the subsequent research.（4）Trans-scale Young’s modulus calculation model of interfacial transition zone was established.With the localization and homogenization method of composite micromechanics,and introduction of calcium hydroxide enrichment coefficient,the macroscopic Young’s modulus of interfacial transition zone is determined.The results suggested that within interfacial transition zone,the higher porosity,the more significant calculation difference based on different void shape distribution function.The thickness randomness exists widely in both cement mortar matrix and interfacial transition zone.By adopting suitable void shape distribution function,the calculated Young’s modulus can satisfy the accuracy of upper limit,lower limit and average value.（5）Based on gradient-like Young’s modulus of interfacial transition zone,the mesoscopic multi-phase constitutive relationship of concrete was established,macro constitutive relationship and failure mode was simulated.Concrete is treated as a complex of mesoscopic massive elements.Concerning the gradient of Young’s modulus and porosity in interfacial transition zone,with the aid of Mori-Tanaka method and Voigt method,mesoscopic multi-phase constitutive relations of mortar-ITZ composite and concrete are derived,distribution of key parameters is analyzed;uniaxial compressive and tensile behavior of concrete is simulated by finite element method,the influence of interfacial transition zone gradient on macro constitutive relation is analyzed.The significant findings that interfacial transition zone gradient influences remarkably on mesoscopic constitutive relationship of mortar-ITZ composite,mesoscopic and macro constitutive relationship and uniaxial strength of concrete.Research in this thesis would promote the refined model of theoretical concrete,providing theoretical reference to engineering structure design and damage analysis of concrete.