Study On Condensation Characteristics Of Recycled Concrete Self-insulation Wall

As a new form of thermal insulation wall in recent years,self-insulating wall has received wide attention.Compared with internal/external thermal insulation wall,self-insulating wall realizes the integration of thermal insulation and structure.It has the advantages of good fire resistance and the same life span as the insulation layer and the building.Existing studies have conducted many studies on the thermal performance of self-insulated walls,but most of them only focus on a single heat transfer and insulation performance,there are few studies on the coupled heat and moisture transfer of self-insulated walls and the characteristics of condensation inside the wall.Based on this background,this paper takes recycled concrete self-insulation walls as the research object,and simulates the coupled heat and moisture transfer process of self-insulated walls based on COMSOL Multiphysics multiphysics simulation software.Combining the heat and moisture transfer analysis of the internal condensation characteristics of the wall,the condensation risks and easy condensation positions of different block forms are obtained,which can provide a reference for the optimization design of the self-insulating wall.This paper mainly conducts research through experimental testing and numerical simulation.The main research work and results are as follows:Firstly,through experiments,the apparent density,isothermal moisture absorption curve,water vapor permeability coefficient,liquid water diffusion coefficient,thermal conductivity and specific heat capacity of recycled concrete with different proportions were measured,and it was found that the thermal and moisture physical parameters of recycled concrete with different proportions are different.In terms of apparent density,as the replacement rate of recycled aggregate increases,the apparent density remains basically unchanged.As the water-binder ratio increases,the apparent density decreases.In terms of thermal conductivity,as the replacement rate of recycled aggregate increases,the thermal conductivity shows a trend of first decreasing and then increasing.The change of water-cement ratio has little effect on the thermal conductivity of recycled concrete.The experimental results show that the thermal conductivity and water vapor permeability coefficient of recycled concrete increase with the increase of relative humidity.This paper presents thier fitting relationship with relative humidity,which provide basic parameters for subsequent numerical simulations.And the wet physical parameters of recycled concrete are also measured through experiments,which provides basic data for the lack of current database of wet physical parameters of building materials.Then,taking the Xi’an area as an example,the COMSOL Multiphysics numerical simulation software was used to simulate the coupled heat and moisture transfer process of recycled concrete self-insulating walls,and the law of coupled heat and moisture transfer inside the wall was obtained.The study found that the self-insulating wall built by self-insulating blocks has a non-homogeneous structure in the thickness and width directions,and because the building materials have different thermal conductivity and water vapor permeability coefficients.The temperature and relative humidity of the points in the wall at the same thickness or width are different.And it is concluded that the junction of recycled concrete near the outdoor side and insulation materials is the most prone to condensation.In addition,the coupled heat and moisture transfer characteristics of recycled concrete self-insulating walls composed of eight different block forms are studied,to analyze the influence of the structure of self-insulating blocks on the condensation characteristics of self-insulating walls.The research results show that as the number of vertical columns of block holes increases,the risk of condensation inside the wall decreases.As the number of horizontal rows of block holes increases,the risk of condensation inside the wall increases.The risk of condensation in the staggered arrangement of two horizontal rows and two vertical rows of block holes is less than that of the in-line block holes.In the cooling season,the risk of condensation in the staggered arrangement of three horizontal rows and two vertical rows of block holes is basically the same as that of the in-line arrangement.While in the heating season,the condensation risk of the staggered arrangement is less than that of the in-line arrangement.