Study On Heat And Moisture Transfer Characteristics Of New Type Assembled Ceramsite Foam Concrete External Wall Panel

Promoting the development of prefabricated buildings is an important measure to facilitate structural reform on the supply side.The application of ceramsite foam concrete in the field of prefabricated building plays a certain role in promoting the development of the construction industry.In this paper,aiming to reduce the cost of production and improve the thermal performance of prefabricated external wall panel,the mix ratio of ceramsite foam concrete material is optimized,the hygrothermal transfer performance of the wall panel is tested by physical experiments,the law of hygrothermal transfer inside the board is researched by numerical simulation and the influence on characteristics and energy consumption of the wall board generated by coupled heat and moisture transfer is analyzed.The main research results are shown as follow:1)An orthogonal test design scheme is proposed to optimize the material mix ratio which takes the thermal conductivity not be greater than 0.18W/(m·K),the dry density not be greater than 700kg/m3and the compressive strength not be less than3.5MPa as a target.The effects of the amount of foam and the water-binder ratio on the optimization index of the material mix ratio are comprehensively analyzed.The optimal ratio is obtained,which is,each cubic meter ceramsite foam concrete requires0.68m3foam,0.42 water-binder ratio,21kg vitrified microbeads,1.1kg polypropylene fiber,0.5kg hemp fiber,4kg gel content,83kg fly ash and 217kg ceramsite.A prefabricated external wall panel with the size of 1200mm×600mm×300mm is trial-produced with the optimal ratio.By experimental measurement,the dry density,compressive strength and thermal conductivity are respectively 639.57kg/m~3,3.52MPa and 0.1510W/(m?K),which meet the multi-objective optimization design performance indicators.2)Taking temperature and relative humidity as driving force,a coupled heat and moisture transfer model of the new ceramsite foam concrete prefabricated external wall panel is established.The hygrothermal transfer performance parameters of this new kind of wall panel which is needed for solving the model is obtained;The hygrothermal transfer performance of this new kind of wall is tested by physical experiment,meanwhile,isothermal sorption curve,the variation law of effective thermal conductivity with equilibrium moisture content and the variation law of moisture transfer coefficient and water vapor permeability with relative humidity are obtained.3)The new ceramsite foam concrete prefabricated external wall panel is physically experimented and numerically simulated for 15 days,by comparing the results of the two methods,it is showed that the mean percentage error of temperature and relative humidity are 2.42%and 6.79%,which are acceptable.The reliability of experiment method for hygrothermal transfer performance parameters and the accuracy of calculation parameter setting for numerical simulation are confirmed.4)Taking Shanghai in hot summer and cold winter zone and Beijing in cold zone as examples,a 5-year-long numerical simulation for hygrothermal transfer performance of the new kind of external wall panel is worked out.The results show that temperature and relative humidity inside the external wall panels in the two regions both irregular periodic changed.The period for the external wall panels in the two regions reach normal condition is 1 year.The relative humidity of each external wall panels in both regions is less than 1.0 without risk of condensation,but the relative humidity is sometimes higher than 0.8 which shows the risk of mold breeding,some measures to prevent moisture transfer are needed.The eastward solar radiation has a greater impact on the load of the summer air-conditioning season of the typical cities in the two climate regions than the winter heating season.Compared with the heat transfer calculation model,the normal summer climate in Shanghai is relatively humid.Ignoring the moisture transfer will cause the cooling load calculation value to be small.However,due to the dry climate in winter,the thermal conductivity of the wall panel is ignored according to engineering experience The heating load value calculated by the value is rather large;for Beijing,due to the dry climate throughout the year,the heating and cooling load values that ignore the moisture transfer are both large.There are 87 pictures,42 tables and 137 references.