Performance of spray-on liners for concrete maintenance holes to external water pressures

The deterioration of maintenance holes (MHs), particularly due to corrosion, is a growing concern as the collapse of a MH can cause safety issues such as sinkholes and they are expensive and disruptive to replace. Spray-on liners are commonly used for MH rehabilitation, but MHs are still prone to fractures and cracks caused by external loads and continued corrosion. These defects expose the liners to water pressure from groundwater. In addition, the performance of liners can be compromised due to de-bonding from the concrete substrate caused by improper surface preparation. However, limited research exists on liner behaviour under such conditions, and standardized testing and design protocols are lacking. This study investigates the interaction between spray-on liners and concrete substrates and proposes a practical test method to determine the critical failure pressure of the liner. Full-scale tests were conducted on a MH with de-bonded areas where the liner was not bonded to the substrate and without de-bonded areas. Additionally, small-scale specimen tests using flat concrete pavers as the concrete substrate were developed and performed. The results showed that failure pressures were similar in the full-scale MH and specimen tests, indicating that concrete substrate curvature did not have an impact. Using the concrete paver specimens, failure mechanisms and critical failure pressures were examined for three liner materials, i.e. epoxy, polyurea, and polyurethane, with varying de-bonded diameters and surface preparation methods. Tensile failure was the critical failure mode for the epoxy liners, and their failure pressure could be conservatively estimated using flat plate theory. In contrast, polyurea and polyurethane liners exhibited a peeling failure mode, with peeling forces per unit length quantified. Adhesion strength tests showed potential for estimating these peeling forces. The findings presented in this paper represent an initial step toward developing a testing protocol and design procedure for spray-on liners used in MH rehabilitation.