Study on the microstructure and water absorption changes of exterior thin-layer polymer renders during natural and artificial ageing
This paper presents the experimental investigation results of exterior render of external thermal insulation composite systems (ETICS). The study involved natural (long-term) and artificially accelerated (short-term) ageing including effect of UV radiation. For research purposes the cycle of accelerated UV radiation ageing test, imitating the impact of one natural year in Lithuanian climate conditions, have been composed and used. In order to determine the visual, microstructure and water absorption changes and find out the correlation between the natural and artificial weathering, the results of tested aged and untreated samples have been compared. The main attention was focused on the changes of structure and physical properties after short-term and long-term ageing tests.
The structural changes of render surface of ETICS after UV tests were determined using scanning electron microscope (SEM). The water absorption of ETIC system was determined by partially submerging. Analysis of render surface microstructure showed that UV rays destroy continuous polymer film on the acrylic and silicone render surface, but water absorption of ETICS does not increase in both cases. Water absorption rates of acrylic, silicon and silicate renders after one natural year of exposure become similar. The polymer film formed on exterior acrylic and silicone render surface was destroyed during one year natural and equivalent laboratory ageing. In conjunction, the carbonization process was taking place, the newly formed calcite crystals covering pores and capillaries, consequently the water absorption rate of all ETICS samples decreased.
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