The Effect Of Permeation Properties Ofconcrete With Initial Defect

The permeability of concrete is part of the important indexes in the design and evaluation of concrete durability.Therefore,it is necessary to study the permeability of concrete.In the meso-scale,concrete is a kind of multiphase heterogeneous composite material,and there are some initial defects in the concrete due to the pouring technology and other factors.In order to investigate the influence of initial defects on the permeability of concrete,the initial defects are divided into void defects and crack defects,and the two-phase mesoscopic permeability model of mortar is established based on the theory of meso-inclusion.Based on the theoretical prediction of the permeability of mortar,the influences of porosity and crack density on the permeability of mortar are considered.The mesoscopic geometry model of two-dimensional three-phase concrete is established based on the random aggregate model.In the finite element numerical simulation software,the macroscopic seepage simulation of concrete geometric model is carried out.The influence of concrete mesoscopic structural parameters on permeability is also discussed.The main work and conclusions of this paper are:(1)The prediction model of mortar two-phase meso-permeability is established.The mortar is seen as a two-phase heterogeneous material composed of zero defect matrix and initial defect.The defects can be divided into void defect and crack defect according to their shape,and the void defects can be divided into two parts: one is the void defect,the other is the crack defect.The void defect,crack defect,composite defect and zero defect matrix are equivalent as equivalent mortar respectively.The permeability prediction model of two-phase meso-equivalent mortar under different defects is established.The prediction results of the model compare with the numerical results,and the validity of the theoretical model is verified.Based on the model,the influence of porosity and fracture density on mortar permeability is discussed.(2)Based on the random aggregate model,the meso-geometric models of three-phase concrete with 20% aggregate content,30% aggregate content and 40% aggregate content are generated.The results show that the generation model is compared with the code.The aggregate content of the model and the number of aggregates in different particle size ranges are within the scope of the specification,which proves the reliability of the random aggregate model generation program used in the paper.A two-dimensional circular random aggregate model with different aggregate content was established,and the finite element numerical simulation software was used to simulate the mesoscopic seepage flow.The simulation results were compared with the mesoscopic theory,and the validity of the simulation method was verified.(3)Based on the orthogonal test,the effects of aggregate content,shape and gradation,interface transition zone thickness and permeability,the content of pore defect and crack defect on permeability are discussed.The results show that the aggregate content has the most significant effect on the permeability of concrete,and the aggregate shape has no significant effect.The permeability of concrete is negatively correlated with the aggregate content,the thickness of the interface transition zone and the permeability,while the relationship between the permeability and the defect content is positive.