- Question: We always have a difficult time hiring good shotcrete nozzlemen. When interviewing nozzlemen, how can we screen those who can shoot well from those who can only talk about shooting?
Answer: Screening and hiring proficient workers can be difficult and time-consuming. Since field workers affect a project's overall quality, it's wise to devote some time to the hiring process. Also, with the costs of paperwork and training for each new hire, it's best to select a good candidate the first time out. Consider using the ACI Committee 506 "Guide to Certification of Shotcrete Nozzlemen" for the screening process. This document suggests having each candidate take a written test and demonstrate workmanship. To quickly narrow the field of applicants, have each one answer the following 10 true/false questions taken from ACI 506. For a copy of the guide, contact the American Concrete Institute, P.O. Box 19150, Detroit, MI 48219 (313-532-2600). Quick Screening Quiz for Shotcrete Nozzlemen Place T (true) or F (false) in the blank after each statement. 1. Dry-mix fine-aggregate shotcrete is also known as gunite. ___ 2. When enclosing reinforcing steel, the nozzleman should: (a) Hold nozzle closer than usual. ___ (b) In dry-mix application, slightly reduce the amount of water entering at the hose. ___ (c) Keep face of bar clean so the steel can be seen until buried. ___ 3. Shotcrete will easily bond to a concrete surface that has been cured with a regular concrete curing compound. ___ 4. Shotcrete rebound should not be salvaged and worked into later batches of materials. ___ 5. In the dry-mix process, a one-to-two mix proportion of cement to sand is considered a lean mix. ___ 6. When water curing is specified, both wet- and dry-mix shotcrete surfaces should be kept moist for a minimum of seven days. ___ 7. Curing fresh concrete is necessary to: (a) Keep surface clean. ___ (b) Minimize shrinkage cracking. ___ (c) Make concrete strong by chemical action. ___ 8. Hose plugs can be caused by: (a) Wet sand. ___ (b) Rocks or caked cement lumps. ___ (c) Poor operation by gunman. ___ (d) Too much water at nozzle. ___ (e) Not blowing out hose when gun is shut down. ___ 9. Sand pockets are caused by: (a) Not curing fresh shotcrete. ___ (b) Slugs from nozzle. ___ (c) Hot sun and wind. ___ (d) Holding nozzle too far from reinforcing steel. ___ (e) Shooting at too much of an angle to the wall. ___ (f) Not shooting into corners first. ___ (g) Shooting over rebound. ___ 10. It is possible for properly spaced reinforcing steel to be moved away from the shooting surface during shotcrete application if the steel is not securely tied back to the shooting surface. ___ Answers: 1. T 2. (a)T (b)F (c)T 3. F 4. T 5. F 6. T 7. (a)F (b)T (c)T 8. (a)T (b)T (c)T (d)F (e)T 9. (a)F (b)T (c)T (d)T (e)T (f)T (g)T 10. T