Before making a mix design for shotcrete or sprayed concrete, it is needed to get sufficient information from the clients. Adequate support information will result in a technically and economically effective for the work. A proper mix design assures a successful trial and thus, successful application on-site.
Hereafter is a list of 9 questions to ask the clients prior to making a shotcrete mix design:
1. The location of shotcrete to be applied? Slope stabilization, overhead and wall in the tunnel.
2. Wet or Dry process will be applied? Normally, dry process for slope stabilization, the wet process for tunnel lining.
3. The requirement of early strength (8 hours, 72 hours, 7 days, 28 days) and the final strength at each location.
4. Slump requirement (for wet process only)
5. What accelerator admixture to be used? Please note that it would be better to use liquid admixture in the rainy season.
6. What is the concrete spraying machine to be used? Rotor Machine (for both wet and dry process) or Pump Machine (wet process only)
7. What kind and type of cement to be used (cement should be super fine. Blain Surface fineness is greater than 4000 square centimetres per gram) PC cement is most suitable for early strength requirement.
8. A dispenser system needs to be installed in case the wet process is used. Is such a liquid dosing unit available?
9. Any other information is helpful in designing the shotcrete mix?
Once these questions get answered, the mix designing process can be started. For shotcrete or sprayed concrete, the trial is a must be prior to the issue of mix design for the actual application.