Experimental study on the long-term behaviors of spray-applied acrylate waterproofing membrane for tunnels exposed to aggressive ions

Abstract

This paper presents laboratory experiments exploring the resistance of an acrylic-acid-polymer (AAP) based, spray-applied waterproofing membrane (SWM) against long-term exposure to aggressive ions (Cl−, SO42− and OH−). The watertightness performance of this SWM exposed to aggressive ions is examined through an innovative penetration device that is designed to measure the penetration of a corrosive solution into the sandwich structure (concrete lining bonded with SWM). Our results show that the SWM maintains excellent resistance to long-term Cl− and SO42− exposure, but incurs swelling and dissolving induced by OH−. The tensile strength of specimens immersed in OH− solution was also found to be reduced by up to more than 90% compared to specimens immersed in distilled water. In addition, SWM exposed to OH− resulted in a non-uniform penetration trace and the largest penetration depth into the specimens, together with severe swelling and dissolving spots on the SWM surface. In contrast, SWM exposed to other solutions resulted in a relatively uniform vapor transport trace. The surface morphology and internal porosity of SWM after three-year corrosion tests were further characterized using scanning electron microscopy (SEM) and X-ray microscopy (XRM). Detailed experimental examinations show that the acrylic-acid-polymer SWM has excellent resistance to a salty and acidic environment, with quite limited resistance to an alkaline environment, which would alter the surface conditions of the SWM and severely decrease the mechanical strength of the internal structures. Our study also indicates that there is an optimal spray distance for SWM (50 cm under tested conditions) and deviation from this distance will aggravate SWM corrosion.