Visualization of localized deformation of external thermal insulation composite systems during aging

Abstract

• The deformation at different hygrothermal aging stages is tested. • The localized non-uniformity of displacement and strain field is highly correlated with the initiation and evolution of cracks in the finish layer. • The influence of temperature and rainfall on the crack expansion and contraction and local non-uniform deformation of the finish layer is analyzed. The localized deformation of finish coat materials occurs due to hygrothermal aging under harsh service conditions, which adversely impacts the thermal performance and safety of the external thermal insulation composite systems (ETICS). In this study, digital images of the ETICS finish coat were obtained using an industrial digital camera under artificially generated harsh aging environment. Both local deformation field and strain field as well as the surface crack initiation and evolution process of the ETICS finish coat were assessed by the digital image correlation method. The calculation results revealed that the phenomena associated with the occurrence of a localized non-uniform displacement field and strain field of the ETICS finish coat during aging are very significant especially at the cracks, with obvious regional boundaries. The localization of the strain field is highly correlated with the initiation and evolution of cracks with a significant local distribution band. The maximum horizontal displacement and vertical displacement during the resting phase after being exposed to rain were reduced by 77.14 and 57.69%, respectively compared with those at high temperature. The massive expansion and shrinkage resulted in the cracking of the finish coat. When the cracked finish coat expands at high temperature or shrinks when exposed to rain, the cracks also expand or shrink accordingly, so that the localized non-uniformity level of the displacement field decreases or increases, and the strain on the reference line presents uniform change or sudden change. The non-uniform deformation of the finish coat caused by the cyclic action of aging factors such as high temperature and rainfall eventually becomes more and more significant. The characteristic index for non-uniform deformation was proposed and its evolution laws with the aging time were systematically analyzed. Taken as the next research focus, it can provide a reference for analyzing the deformation and deterioration process of the ETICS and ensuring the operation safety.