A conference was conducted to discuss the making, testing, and using of shotcrete for underground support. With regard to the making of shotcrete, quality control was considered essential. It was believed that average 28-day compressive strengths in the range of 3,000-4,000 psi (20.6-27.5 million N/sq m) were more realistic than the presently specified 5,000 psi (34.4 million N/sq m) compressive strength at 28 days. Opinion on the maximum size of coarse aggregate to be used in a shotcrete mix favored at least 1/2-inch (13 mm) maximum size. The importance of compatability tests of the cement and accelerator to be used was emphasized. Though remotely controlled nozzles and wet mix shotcrete equipment has had wider use in Europe, there was considerable interest shown in the use of skilled nozzlemen as employed in the U.S. Cube, core, probe, impact, and pull-out tests were discussed, and it was concluded that such tests need further development. In discussions of where to use shotcrete, it appeared that shotcrete offered economies in nominally unlined water tunnles built by the drill and blast method, where it could serve the dual function of support and final lining. It also appeared to offer economies where a drill and blast tunnel had a persistent need for support and coverage of the rock to prevent deterioration due to moisture change or stress relief. Though it is not believed to be presently compatible with the tunneling machine, an example was presented where a tunneling machine had been designed to accommodate the use of a specific shotcrete system.

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Filing Info

  • Accession Number: 00260465
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 11 1974 12:00AM