Effect of various artificial ageing procedures on adhesive joints for civil engineering applications

Abstract For civil engineering applications of adhesive bonds, the service lifetime and environmental ageing is a fundamental question for safe design. The paper compares the effects of three different ageing procedures (immersion in warm water according to ETAG 002, neutral salt spray test according to ISO 9142, Procedure E4, and extended cataplasm test based on ISO 9142, Procedure E2) among each other on adhesives which are applicable in the civil engineering field. The research covers two different adhesives (two-part acrylate and silane terminated polymer, STP) applied in double lap shear joints composed of aluminium and Zn-electroplated steel substrates. Aluminium was used in two types of alloy and also as anodized aluminium due to its wide use in building facades. All mechanical test results were put in context with chemical analysis results to better understand the changes in the adhesive joint after environmental ageing. Based on infrared spectroscopy, we observed hydrolysis for both tested adhesives, which was more significant for the acrylate adhesive after immersion in water according to ETAG 002 and for the STP adhesive after the neutral salt spray test. Moreover, water and higher temperatures lead to the decomposition of the polymer structure in the case of the acrylate adhesive, which explains the reduction of significant mechanical properties (often more than 60%) after all types of laboratory ageing procedures. The STP adhesive showed lower mechanical properties worsening (about 30%) than the acrylate adhesive caused by hydrolysis. Changes in polymers were futher examined by the water absorption test and the determination of the glass transition temperature by DMA. It was confirmed that the STP adhesive has a better water resistance than the acrylate adhesive due to lower water absorption rates and no significant changes in Tg after immersion.