GeneralQ In placing shotcrete in layers, what is the recommended thickness of each layer?
Appropriate thickness of the shotcrete layers is impossible to generalize because it depends on many factors, including:
- The type of shotcrete (wet- or dry-mix);
- The texture and stiffness of the receiving surface;
- The physical properties of the fresh concrete used, including a) w/cm ratio; b) slump; c) use of accelerator; d) type of supplementary cementitious materials used in the mixture (microsilica, fly ash, and slag); e) fibers used in the mixture; and f) mixture temperature;
- Weather conditions—Is it hot or cold, dry or wet, and/or windy or calm?;
- The shotcrete equipment used: a) type of nozzle; b) distance from the receiving surface; and c) air pressure and air volume;
- The orientation of the shotcreting (vertical/sloped/overhead)
Experienced shotcrete contracting firms using ACI Certified Nozzlemen have a wealth of experience in evaluating all these factors to achieve the proper results. You may consider subcontracting the shotcrete work to an ASA member contractor with experience in this type of work. You can submit your project details for bids from our ASA Corporate Members using the Web form at shotcrete.org. For further reference, ACI 506R-05, “Guide to Shotcrete,” provides some general discussion of the shooting techniques that may be appropriate. Retaining an engineer or shotcrete consultant experienced in shotcrete application may be of value to assist in evaluating your specific factors and recommend the best solution.
