Study On Structure And Performance Of Cast-in-place Urea Formaldehyde Exterior Wall External Insulation Systems

Currently, organic insulation materials such as polystyrene board are widely usedin China, but the inflammability causes potential safety hazard, which hinders theapplication of them. Urea formaldehyde foam insulation, a new insulation materialintroduced from abroad, has numerous advantages including non-flammability, lowprice and excellent thermal insulation performance. So it has attracted professionals’interest and have high market competitive power. However, in China recently, ureaformaldehyde foam insulation is only used in sandwich thermal insulation wall and roofinsulation system, which is not studied deeply and comprehensively. In order to studyproperties of urea formaldehyde foam insulation and design proper structureconstructions for exterior wall external insulation, the material experiments and theoptimization of insulation construction are conducted. The following jobs are mainlyfinished in this paper.1)The manufacture of urea formaldehyde foam is self achieved successfully. Somematerial experiments are carried out to determine the performance index of ureaformaldehyde produced under different formula. For the sake of providing necessarymaterial parameters for the finite element simulation, the materials of connectors anddecorative boards in exterior wall external insulation structure, ABS plastic and calciumsilicate board, are also studied in material tests. It is shown that the thermal conductivityof urea formaldehyde foam insulation is very small as low as0.292W/(m·K), whichmeans excellent thermal insulation performance.2) Temperature tests are designed, which mainly focus on urea formaldehydefoam’s linear expansion coefficient and related influences from density and moisturecontent. Moreover, the finite element simulation needs shrinkage strain of the insulatinglayer in exterior wall exterior insulation structure, so they are determined in the dryingshrinkage experiment of cast-in-place urea formaldehyde foam. It is shown that ureaformaldehyde foam’s linear expansion coefficient is around18106/℃(maximum is19.64106/℃). It goes up with the increasing moisture content, and the density of thematerial has little influence on the linear expansion coefficient in certain extent. Theoverall shrinkage strain1.62102is taken into account in model calculation toconsider the influence of the insulating layer’s shrinkage on the structural force.3) The finite element software ABAQUS is utilized to simulate two self-designedconstruction of exterior wall external insulation structure under shrinkage of insulatinglayer and wind load by model building. According to different design requirements,rational and safe construction size schemes of the both are put forward to optimize thedesign. 4)Urea formaldehyde foam insulation used the brittle cracking constitutive modelin ABAQUS as its constitutive relation to investigate the possibility of insulating layerforming into heat bridge because of crack propagation. On the basis of simulationresults, the cracks in insulating layer mainly appear around connectors, with the crosspropagation path. There are two cracks around each connector, and the maximum widthof cracking region is5.2mm, while the average is3.5mm. Because the cracking widthshowed in the simulation is much larger than the actual value, the construction schemecan meet the rules of not forming heat bridge in the insulation layer in the standard.