Adhesive bonding as an alternative for underwater structural repair

An acrylic adhesive is offered as an alternative to welding for onsite underwater structure repair. The resin -viscosity is adjustable through the addition of liquid viscosity modifiers and reinforcing fillers to the formulation. The underwater resin solidification can be achieved "on-demand" by a photo-polymerization process: Resin cure is accomplished typically by a 15-second high intensity, blue illumination (25 to 100 W/m(2)) with a retrofitted diving flashlight. Lap shear strength ranges between 2 and 6 MPa (300 and 900 psi), depending on the illumination time, the light intensity and the substrate condition. Bonding has been performed successfully on a wide range of submerged surfaces: bare, rusty and painted steel, concrete, wood, fiberglass, brass, bronze and aluminum. For fouled surfaces, a preparation treatment that can be applied underwater before bonding has been designed and strongly improved the adhesion strength. Bonding in brine water versus tap water does not affect bonding and the strength results. In addition, no effect of water temperature has been detected between 1 and 40 degreesC (32 and 104 degreesF). Bond aging in water at room temperature showed an increase in tensile strength during the first week of immersion, followed by a drop towards a plateau situated at 1/3 of the initial strength value. The filled resin (ready for use) can be stored at room temperature for months in a dark container. If the resin is subjected to higher temperatures, some presolidification occurs locally in the container, but the liquid fraction displays similar cured strength characteristics when illuminated.