RepairQ Our current project is a pier with severe corrosion of reinforcement and obvious spalls. The work will all be overhead with the surface 18 in. (457 mm) above the mean tide level and, for a variety of reasons, dry-mix is not an option. We are looking for a good, dense, wet-mix design for saltwater marine exposure. Compressive strengths need to be in the mid-range of 7000 to 8000 psi (48.3 to 55.2 MPa).
For a potentially suitable wet-mix shotcrete mixture design for marine structure repair, go to the ASA Web site (shotcrete.org). Click on Shotcrete magazine and search for “Shotcrete Classics: Deterioration and Rehabilitation of Berth Faces in Tidal Zones at the Port of Saint John.” This mixture design worked well for over 1.2 miles (2 km) of ship berth face repair over a 10-year period. Note: Because of high freezing-and-thawing exposure, the shotcrete was required to be air entrained. While the original mixture design called for 7% air content as shot, it was subsequently modified to require an air content of 7 to 10% as batched (at the point of discharge into the shotcrete pump) and an air content of 5 ± 1.5% as shot (into an air pressure meter base). Such shotcrete has provided good freezing-and-thawing resistance. You should be aware that your local materials (coarse and fine aggregates and cement) may have different properties in the concrete mixture, however, as compared to the mixture discussed in the article. It is recommended that a local engineer, testing laboratory, or concrete supplier be retained to develop a concrete mixture using local materials that meets the performance requirements of the mixture design mentioned in the article. Also, test panels constructed with the mixture, nozzlemen, and equipment to be used in the shotcreting are highly recommended to verify the strength performance of the shotcrete.
