RepairQ I have a seawall with a gunite (dry-mix shotcrete) outer layer. The gunite layer has cracked in multiple locations on the seawall resulting from years of exposure to the harsh environment. The original gunite was not part of a soil nail system. I am considering a re-coat of shotcrete probably 3 to 4 in. (76 to 100 mm) thick with wire mesh and L-anchors on a 2 to 3 ft (0.6 to 0.9 m) grid. I know the importance of surface treatment for bonding, etc., but I am not sure if I should remove the original gunite layer (which is still sound in some places) or apply the re-coat. The new overlay needs to be structurally effective. I know that a soil nail system is the most dependable solution, but cost is a major concern. Do you have any suggestions?
The new shotcrete layer can be added to the existing shotcrete or installed after the existing shotcrete is removed. The decision to remove or not remove the existing shotcrete is beyond the scope of what we can comment on. If the existing shotcrete is left in place and overlayed, it should be thoroughly cleaned and roughened to create a good bonding surface. Because this is in a marine environment and you are considering the use of wire mesh, you need to make the new layer thick enough to have sufficient cover on the reinforcing steel. Alternately you could consider the use of fiber-reinforced shotcrete and silica-fume-enhanced fibrous shotcrete. Please note that there are many types of fibers on the market. We recommend that you review some of the Shotcrete magazine articles on fibrous shotcrete and on shotcrete in a marine environment on the ASA Web site. We suggested two papers for reference. The first is by Gilbride, Bremner, and Morgan on the Port of Saint John, and the other is by Morgan on the use of fibers that cover marine repairs. You mentioned using “L-anchors” at 2 to 3 ft (0.6 to 0.9 m) spacing. The use of grouted anchors with a reasonable embedment is quite common, but the design of such anchors is again beyond the scope of what we can advise.
