Improving water resistance of acrylate adhesive joints through atmospheric plasma treatment for civil engineering applications

For civil engineering applications, the service lifetime of adhesive joints and their resistance to environmental ageing are critical for safe design. Water exposure is among the most harmful ageing scenarios, significantly weakening adhesion at the substrate interface. This study evaluates the influence of atmospheric plasma treatment (Diffuse Coplanar Surface Barrier Discharge -DCSBD) on the water resistance of acrylate adhesive joints used in double lap shear configurations with aluminium (including anodised) and Zn-electroplated steel substrates. Mechanical properties and failure modes were assessed before and after immersion of specimens in warm water for 21 days, comparing three surface preparation strategies: the effects of plasma treatment alone, plasma combined with a solvent-based adhesion promoter, and the promoter alone were compared to study changes in joint durability. DCSBD treatment significantly improved the shear strength of anodised aluminium and galvanised steel specimens (by 102% and 70%, respectively) after immersion, compared to specimens without plasma treatment that were also exposed to immersion. Plasma treatment improved the adhesion of the acrylate adhesive to all metal substrates studied; however, this effect was observed only when the solvent-based adhesion promoter was also applied. In the absence of the adhesion promoter, adhesive failure predominated and shear strength decreased for all substrates compared to the reference specimens. This synergistic effect suggests that the combination of plasma treatment and adhesion promoter enhances the bonding mechanism, leading to superior joint performance at some metal substrates, particularly under challenging conditions such as water immersion. • Combined plasma and chemical activation improves water resistance of acrylate adhesive joints on anodised aluminium and galvanised steel. • Plasma treatment alone is insufficient for long-term adhesion without a solvent-based adhesion promoter. • Shear strength of anodised aluminium joints increased by 102% after immersion when plasma and activator were used together. • Non-destructive ultrasonic testing confirmed improved interfacial bonding quality in plasma-treated specimens.