Study Of External Wall Insulation System Based On Gelationous Powder And Expanded Polystyrene Pellets And Its Anti-cracking Properties

The polystyrene powder has been widely used in the external wall thermalinsulation system due to its super insulation ability，good stability，easy constructionprocess and low cost. The polystyrene powder insulation system is one of the popularinsulation systems in various regions of China with large temperature gap betweensummer and winter. However，there are drawbacks occurring to the polystyrene powder.The polystyrene powders possess low strength，high water absorption，high shrinkstress，easy cracking and safety issue. In addition，the polystyrene powder insulationsystem occasionally cracks，leakages，and chips. In this dissertation，the formation andmechanism of cracking of polystyrene powders and insulation system are investigated.From the material and insulation system points of view，the utilization of polystyrenepowders and the insulation effect of polystyrene powders and insulation system havebeen dramatically improved by preventing the insulation system from cracking.The surface treatment of polystyrene powders has been systematically investigatedto increase the adhesive ability. We use the coupling agents and binding agents to form ahydrophilic shell on the hydrophobic polystyrene powders. The hydrophilic shell on thehydrophobic polystyrene powders increases the adhesion between the polystyrenepowders and cementitious material. The improvement of adhesion by the hydrophilicshell with the cementitious material is one of EPS surface treatment techniques freewith the organic binders. This low cost surface treatment technique guarantees theavailability of polystyrene powder insulation mortar for the mass production.The effect of the graduation and morphology of polystyrene powder，polymerbinders，water retention agents，polymer fibers，poly-silicon water proof agents on theinsulation mortar has been investigated systematically. The use of re-dispersed emulsionpowders can increase the construction ability and adhesion of the insulation mortar andimprove the toughness of the insulation system. The adding amount of the emulsionpowders has to be controlled within5.0~6.0kg m3.Methyl cellulose ether is theeffective water retention agent. However，it will decrease the strength of the insulationsystem as the ratio between water and cement increases.The adding amount of themethyl cellulose ether has to be controlled within1.5~1.7kg m3.The polypropylenefibers can prevent the insulation mortar from shrinking and increase the toughness andthe anti-cracking ability of hardening insulation mortar. The length of the polypropylene fibers has to be controlled within8~12mm. And the adding amount of thepolypropylene fibers has to be controlled within0.7~1.0kg m3. The organic siliconwater-proof agents can significantly decrease the water adsorbing ability and improvethe water-proof ability. The adding amount of the organic silicon water-proof agents hasto be controlled to be0.6kg m3. We have prepared the polystyrene powder mortar witha superficial density of230Kg/m3，the thermal conductivity of0.056W/cm，compressstrength of0.8，shear bond strength of0.117，absorbing ratio of2.5%，dry shrinkage of0.872‰by surface treatment on polystyrene powder，adding of polymer binders，polypropylene fibers， and so on. The homemade polystyrene powder mortar isadvantages in easy construction process，strength，water-proof，anti-cracking over thetraditional insulation mortar.The anti-cracking mortar is one of the most important components in the insulationsystem. We have investigated the configuration regulation and the physical mechanicalproperties of anti-cracking mortar with special fine sand. We found a regular effect ofthe content of special fine sand and modulus of fineness on the strength and shrinkageratio of mortar. We have prepared the anti-cracking special fine sand mortar with tensilebond strength of0.96MPa，cracking index of1.6，shrinkage of0.565‰in56days.After28days of hardening，the anti-cracking special fine sand mortar possesses astriking energy of8.7J，cracking energy of300.3J m2，and maximum deformation of3.02mm.We have investigated the stress strain behavior of the polystyrene powderinsulation system in the extreme high or low temperature in Chongqing by finiteelement numerical simulation. It was found that the insulation layer has the maximumtemperature gradient and strain，while the anti-cracking layer has the maximumtemperature stress. At the summer with extreme high temperature，the maximum stressof anti-cracking. Therefore，the location with maximum probability of cracking has tobe pre-strength. The stress concentration occurs at the inside corner，outside corner andparapet wall. The widths of stress concentration at the inside corner and outside cornerare0.05and0.08. The widths of stress concentration at the parapet wall are0.35and0.25at plane and parapet orientations，respectively. The anti-cracking layer withconcentrated stress can be strengthened by fiberglass mesh cloth to conquer theinfluence. The four corners at the window hole will meet the concentrated stressphenomenon. The range is about0.32m0.84m with an angle of45from the hole.However，the area of the region of the stress is independent of the size of the hole. In addition there is the stress release occurring at the surround of the hole except thecorners. The polystyrene ribbon at the expansion joint has low elastic modulus. It willrecover under a large stress and strain，which can absorb the stress and strain created bythe temperature variation. The width of the expansion joint has to be larger than8mm.And the interspace between two joints has to be smaller than6m.We have produced the polystyrene powder insulation mortar and anti-crackingspecial fine sand mortar with mass production. We have used them in the buildings ofthe Longhu real estate. To improve the anti-cracking ability，we have put the horizonexpansion joint with a size of10×30mm in every distance of3m.We also use thefiberglass mesh with anti-alkaline treatment at the inside corners，outside corners andparapet corners with occurrence of the concentrated stress. At January2012，we begin toconstruct and it only took two months to finish. At May2012，it was passed through theexamination of building energy saving by the quantity supervision station.The exportershighly appraised the quantity of the construction.