Study On Transmission Characteristics Of Coupled Heat And Moisture Transfer Of Cast-in-Situ Concrete Wall On Thermal Insulation Free From Demolition Template In Cold Area

The cast-in-situ concrete wall on thermal insulation free from demolition template is a new type of wall technology that integrates insulation and structure.It represents a new direction in the development of building energy-saving techniques.The study of the thermal and moisture characteristics of the cast-in-situ concrete wall on thermal insulation free from demolition template is of great significance for its widespread application.By combining theoretical analysis,experimental testing,and numerical simulation,a mathematical model for the coupled heat and moisture transfer of the insulated concrete wall with a removable insulation formwork was established.The thermal and moisture transfer performance parameters of the wall materials that needed experimental testing were determined.The optimized mix ratio of the auxiliary insulation material for the removable insulation formwork was proposed.The thermal and moisture transfer performance parameters of the wall materials,including C50 concrete,XPS,and auxiliary insulation materials,were experimentally tested.The internal heat and moisture transfer characteristics of the wall were studied through experiments and numerical simulations.The main research achievements are as follows:1)The optimized mix ratio of the auxiliary insulation material for the removable insulation formwork was proposed.An orthogonal experimental design with four factors(water-cement ratio,cellulose ether,polypropylene fiber,and hemp fiber)at four levels was conducted.The results of the orthogonal experiment were analyzed using range analysis,variance analysis,and matrix analysis to obtain the optimal mix ratio.The products produced according to this formula showed improved thermal and mechanical performance.2)A mathematical model for the coupled heat and moisture transfer of the wall was established,and a database of thermal and moisture transfer performance parameters of the wall materials was developed.By taking temperature and relative humidity as driving forces,a mathematical model for the coupled heat and moisture transfer of the insulated concrete wall with a removable insulation formwork was established.The thermal and moisture physical property parameters of the wall materials required for solving the mathematical model were experimentally tested,including dry density,porosity and pore size distribution,liquid water diffusion coefficient,moisture characteristic curve,thermal conductivity,and water vapor permeability coefficient.The relation of diffusion coefficient of liquid water with equilibrium moisture content,water characteristic curve,effective thermal conductivity with equilibrium moisture content,water vapor permeability coefficient with equilibrium moisture content.3)A calculation model for the freezing temperature of water inside the wall materials was established.Based on the pore size distribution characteristics and moisture characteristic curve measurement of the wall materials,a method for calculating the equivalent pore size of the wall materials was proposed.Using the phase equilibrium theory and Gibbs-Thomson equation,a calculation model for the freezing temperature of liquid water inside the equivalent pore size was established.The variation law of the freezing temperature of water inside the wall materials and the calculation formula for the unfrozen water content inside the materials were obtained through experiments.The relative errors between the calculation model results and the experimental test results were all less than 5%,which met the engineering requirements and verified the accuracy and reliability of the calculation model.4)The coupled heat and moisture transfer laws of the wall under low-temperature conditions and the internal heat and moisture transfer characteristics of the wall in different climatic regions were studied.A test device for studying the coupled heat and moisture transfer of the wall under low-temperature conditions at-20°C was designed and built.The temperature and humidity distribution inside the wall under the-20°C low-temperature condition were studied through experiments and numerical simulations.The trends of the numerical simulation results and the experimental test results were consistent,and the errors met the engineering accuracy requirements.The thermal and moisture characteristics of the insulated concrete wall with a removable insulation formwork in two typical cities,Beijing and Harbin,in cold and severe cold regions were studied through numerical simulations for a period of five years.The internal and surface condensation and frost risk were analyzed,and the energy consumption characteristics were calculated.The thesis contains 105 figures,48 tables,and 129 references.