Research And Application Of Mesoscopic Simulation Method Of Concrete Hardening Damage

Concrete is a typical kind of hardening material.In the process of hardening of concrete,the shrinkage strain of cement mortar will generate self-constraint stress and micro cracks internally.Currently,the researches on the laws of generation,distribution and evolution of the micro cracks of concrete in the process of hardening are adequate.The researchers in mesoscopic mechanics field are just studying the mechanical behavior of hardened concrete.The preliminary defects are given in some random distribution form but the form and size for distribution are short of theoretical basis.In this paper,researches are conducted on the numerical simulation of self-constraint stress and self-constraint micro cracks in the process of hardening of concrete.The whole paper can be divided into four parts,including the construction of numerical geometrical model,construction of microscopic hardening model,stimulation of concrete hardening process,and application researches.The main research results are as follows:1.On the basis of Two and Three Dimensional Discontinuous Deformation Analysis(DDA),the sample-forming method for the mesoscopic numerical of concrete is put forward,and the packing software for concrete aggregates is developed which realizes the packing of four-graded aggregates and large-content aggregates.The research results show that the DDA-based packing method increases the limit value of the Three-dimensional packing content of aggregates from 60% to 75%,meeting the actual demands on concrete aggregate contents.2.The concrete mesoscopic damage and fracture computational model which considers the concrete hardening effect is proposed.In this model,the factors that temperature,elastic modulus,creeping,and autogeneous shrinkage strain varies with the concrete age in the process of hardening has been taken into consideration.Besides,the development and verification of program are conducted,providing a solution to the mesoscopic numerical stimulation for micro-cracks generated in the hardening process.3.On the basis of the advanced numerical stimulation method for concrete mesoscopic hardening,meso-scale researches are carried out in the process of concrete hardening,and the self-constraint stress distribution laws and generating mechanism for self-constraint micro cracks in the hardening period are revealed.The numerical loading experiment method is applied to estimate the effects on basic mechanical properties of concrete imposed by self-constraint micro cracks.The results of researches are as follows: self-constraint stress for mortar interface within concrete is in normal distribution,and there is an exponential relation between the number and length of self-constraint micro cracks.Micro-cracks account 80% of the interfacial cracks.The self-constraint micro cracks impose a significant deteriorating effect on the concrete performance.The creeping of concrete,autogeneous shrinkage strain and strength of interfacial transition zone impose a significant impact on the generation of micro-cracks.4.Numerical simulation method for meso-hardening of concrete is applied to study two engineering problem,including the concrete cracks induced by pipe cooling and non-stress meter measuring reliability of dam security monitoring.The results show as follows: as for the cooling of water pipes,there is a significant difference between the cooling damage zone depth of homogeneous model and non-homogeneous model.When the temperature difference for cooling water pipes is over 10?,the cooling damage imposes a significant impact on the crack resistance performance of concrete.As for the non-stress meter measuring reliability,the results show the eliminating manner for big aggregates in non-stress meter embedding is conducted imposes a significant impact on non-stress meter measuring results.