27 Ian Moore White Paper

Abstract

Various sprayed repair systems are available to rehabilitate drainage infrastructure. These include epoxy, polyurea, and polyurethane sprays used on the inner surface of reinforced concrete maintenance holes to seal against leakage and to protect the concrete from biogenic corrosion. It also includes cementitious materials used to restore hydraulic integrity and the structural capacity of sewers and highway culverts. This paper summarizes recent work to understand the strength limits of these repair methods, and to develop design equations that permit consultants to select appropriate liner thicknesses, and to assess the impact of loss of bond between the sprayed liner and the host pipe. Firstly, the polymer sprays are investigated by considering a circular zone of material where bond has failed to develop between the spray and the substrate. Failure of the liner is either by fracture or peeling, and the allowable size of the debonded region will depend on the groundwater pressure, the tensile strength of the liner material, and the resistance of the bond between the liner and the substrate. Next, design methods to select the required thickness of cementitious sprays on corrugated metal pipes are described, considering either bonded (i.e. composite) or unbonded interaction of the liner with the corrugated steel. Finally, new methods for selecting the required thickness of cementitious sprays on reinforced concrete pipes are outlined, considering the condition of the pipes being rehabilitated.