Study On The Thermal Performance Of Foamed Concrete External Panel Of Prefabricated Building

The prefabricated building has become the trend of China’s construction industry and an important way to realize the modernization of the construction industry.The application of external wall panels is the key index for measuring the industrialization level of buildings.Prefabricated foam concrete wall panels will be widely-used in prefabricated buildings.However,the strength and thermal performance of common foam concrete wall panels are mutually restricted.So it’s very important to study the production and utilization technology of prefabricated foam concrete wall panels which have good thermal performance and meet the performance requirements for the development of prefabricated buildings.With the dry density grade 700 kg/m3,the compressive strength 3.5MPa and the thermal conductivity 0.18W/(m·K)as the design target,the mixture ratio of the raw material and the base of the foam concrete is determined.Through the orthogonal test,the mix ratio is optimized.The module size and the reinforcement mode of the outer wall panel are set up.The test production is organized and the thermal performance is also made.And the applicability is studied to provide the basis and reference for the thermal performance,HVAC load and building energy consumption calculation in the application process.The main conclusions are as follows:(1)The mixture ratio of raw material and foundation for the production of foam concrete under the design target is determined.The dry density and compressive strength of the foam concrete can meet the requirements,but the thermal performance needs to be further optimized.A four-level four-factor orthogonal test scheme was designed with foam,water gel ratio,aerogel content and fiber content as factors.The orthogonal test results were analyzed by the difference analysis and analysis of variance.Also,the best mixture ratio was obtained by multi index comprehensive analysis,that is,the content of 1m3foamed concrete cement was 332 kg,the content of fly ash was 83 kg,the ratio of water to water was 0.48,the content of foam was0.7m3,the content of ceramsite was 217 kg,the content of vitrified microbeads was 21k g,the content of aerogel content is 4 kg,the content of ceramsite was 1.1 kg and the content of discarded hemp fiber was 0.5 kg.The dry density,thermal conductivity and compressive strength of the specimen produced by the optimal mix ratio are673.12kg/m3,0.1623W/(m·K),4.12 Mpa.(2)The module of 2000mm(high)×600mm(wide)×300mm(thick)double side reinforcement was produced by the optimal mix ratio.The test results met the design goal,and the feasibility of the mix ratio was verified.(3)The test result of the heat transfer coefficient test of the 300mm thick and double stiffened modulus board wall is 0.51W/(m~2·K).The numerical simulation result of ANSYS is 0.54W/(m~2·K),and the difference between them is 5.6%.It shows that the numerical simulation method is feasible to study the thermal performance of the wall.The wall panels meet the design requirements of the 4 or more residential buildings in the current cold area(B).The effective thermal conductivity of wall panels with the same reinforcement thickness of 150mm,175mm,200mm and 250mm is determined by numerical simulation method.(4)The unsteady heat transfer characteristics of the 300mm thick modulus external wall panel under the periodic boundary condition are studied by numerical simulation.The attenuation multiplier is 96.3,the delay time is 11.83h and the coefficient of heat storage on the wall surface 2.48W/(m~2·K),wall thermal inertia index is 4.15,which has a certain attenuation delay effect on the temperature wave of the outdoor periodic change.(5)The simulation results of energy consumption of DesT-h show that the energy saving rate of a 6 layer assembly building using this wallboard has reached67.8%.The comprehensive evaluation model of the external wall panel is established by using the priority and analytic hierarchy process(AHP),which takes the economy,fire resistance,weight of the wall and the process of construction as the evaluation index,and the applicability of the developed exterior wall is evaluated synthetically.