Refer to ACI 506.1R-08, “Guide to Fiber-Reinforced Shotcrete,” at www.concrete.org for guidance on fiber types and dosages. Glass fibers are seldom (if ever) used in shotcrete because they tend to break under the high velocity required for shotcrete. Steel or macrosynthetic fibers should be used at about 0.4 to 0.5 volume percent to control hardened shotcrete cracking, 50 to 66 lb/yd3 (30 to 39 kg/m3) for steel (specific gravity (SG) of 7.85), and 6 to 7.5 lb/yd3 (3.6 to 4.5 kg/m3) for macrosynthetic polypropylene (SG of 0.91). Fiber suppliers can provide more technical guidance for their products. You can locate fiber suppliers by visiting the ASA Online Buyers Guide at www.shotcreteweb.wpengine.com/pages/products-services-information/buyers-guide/.
Are there any guidelines/regulations as to how close in proximity the installer/nozzle person can be to the receiving surface? I have a chimney job (existing chimney repair) that has an opening of 3.5 x 3.5 ft (1.1 x 1.1 m) and the interior is calling for a gunite (dry-mix) liner to be installed. Is there an issue with splash-back or any other concern with using gunite in such a confined space?
When gunning in tight areas, you have to allow for the bend in the hose and the length of the nozzle, which will require at least 2 to 2.5 ft (0.6 to 0.8 m). An area 3.5 ft (1.1 m) wide is a very tight area to gun in, but it can be done. In areas that restricted, it’s not possible to always maintain a 90-degree shooting angle, so you will get much more rebound from the deflection when shooting at less than desirable angles. Also, with the dry process, you have to reduce the air pressure and volume to keep from blowing the material off the walls. Ideally, you would like the nozzle to be at least 3.5 to 5 ft (1.1 to 1.5 m) from the receiving surface, depending on the nozzle you use. For a tight area like you are proposing, in addition to reducing the air pressure and running it slowly, we would recommend using a double-bubble nozzle, as it has a wider spray pattern, allowing the nozzleman to be closer to the receiving surface and still get an adequate spray pattern. A double-bubble nozzle is also flexible, which will help in extremely tight areas. You can locate organizations that sell a range of nozzles by visiting the ASA Online Buyers Guide at www.shotcreteweb.wpengine.com/pages/products-services-information/buyers-guide/.
I am searching for a sample specification that calls for the use of a polymer-modified cement mortar in lieu of one that does not have the polymer additive. My thought is that this material would be more durable. I am also wondering if it would have greater bond to the old substrate.
Most of the industry does not endorse the use of polymer-modified additive in shotcrete. Please refer to ACI RAP Bulletin 12 and ACI 506R for further information and insight from the American Concrete Institute (ACI) at www.concrete.org. Shotcrete applied by competent contractors to properly prepared surfaces exhibits excellent bond characteristics to the substrate. Additionally, a good shotcrete mixture that is properly applied will yield a durability equal to or superior to cast concrete. There are many examples discussed in various articles of Shotcrete magazine at shotcrete.org/archivesearch/ArchiveSearch.asp.
I am working on an existing slope with a ratio of 3:1 (horizontal:vertical) and a total height of 6 ft (1.8 m). The slope has been surfaced with asphalt concrete. Will shotcrete adhere to the asphalt concrete surface, or should the asphalt concrete be removed prior to applying shotcrete?
Shotcrete will adhere to properly prepared asphalt concrete. Shotcrete bond is generally related to the preparation of the surface that you want to bond with. If the surface is dirty, the shotcrete will not bond very well.
We are proposing a project that will use shotcrete on an existing metal bin wall to match recently constructed soil nail walls with shotcrete facing. What is the proper way to prepare the bin-wall surface? Also, what type of reinforcement would you recommend and what is the suggested method of attaching the reinforcement to the bin wall?
The surface should be cleaned using a high-pressure water blaster or sandblasting to remove any loose material and rust. If the metal bin material is thick enough, you might want to consider welding metal studs or nuts to the bin to secure the reinforcing steel or mesh. The amount and type of reinforcement is beyond the scope of our organization and we suggest getting guidance from a qualified engineer. You may gain some insight from the design of the reinforcing used in the soil nail walls.
Can a shotcrete mixture be designed using crushed washed sand instead of natural washed sand?
The grading of fine aggregates, natural or manufactured, should be in compliance with the combined aggregate gradations in ACI 506R or ASTM C1436. Using crushed washed sand will be more difficult than using natural washed sand due to the more angular particle shapes. Due to the more angular particles, crushed sand will likely require a higher paste content to successfully convey it through the shotcrete hose.
Type CA and FA shotcrete are two classifications listed in ASTM C1480. What is the application of these two types of shotcrete?
Type FA shotcrete uses a fine aggregate meeting the requirements of ASTM C1436 Gradation #1. Type CA shotcrete uses a combined aggregate gradation meeting the requirements of ASTM C1436 Gradation #2. The decision on which type to use depends on the application, shotcrete thickness, specification requirements, and perhaps the shotcrete equipment to be used, that is, wet- or dry-process. For example, one may want to use Type FA if using dry-process equipment and placing thin sections, or when a smooth finished surface texture is required. For thicker sections, Type CA shotcrete may provide the best properties for the application. The choice of which to use depends on the application, equipment, and experience of the contractor.
I have a question on cold weather shotcreting. I have heard that for shotcrete operations, the ambient temperature has to be 40°F (4.4°C) and rising. I am on a job, and the inspector said it only needs to be 35°F (1.67°C) and rising. The high for the day is expected to be around 45°F (7.2°C), then fall back into the high 20s F (–4 to –1.67°C). What would be your advice?
Shotcrete is concrete and the same rules apply with respect to cold weather applications. Cold weather is defined in ACI 306R, “Cold Weather Concreting” as “a period when, for more than 3 consecutive days, the following conditions exist: 1) the average daily air temperature is less than 40°F (4.4°C) and 2) the air temperature is not greater than 50°F (10°C) for more than one-half of any 24-hour period.” ACI 306R is an excellent reference that provides recommendations for cold weather concrete placement and protection. A copy of ACI 306R can be purchased online at ACI’s Web site, www.concrete.org, from the Bookstore and Publications tab. You can also download articles regarding cold weather placement from ASA’s Web site, shotcrete.org—click on “Shotcrete magazine,” go to the article search page, and type in “cold weather.”
Users should check the ASA on-line bookstore for the latest version to purchase. If not available in the ASA Bookstore, contact the authoring organization.
American Concrete Institute (ACI)
www.concrete.org
- ACI 506R, “Guide to Shotcrete”
- ACI 506.1R, “Guide to Fiber-Reinforced Shotcrete”
- ACI 506.2-13, “Specification for Shotcrete”
- ACI 506.4R, “Guide for the Evaluation of Shotcrete”
- ACI 506.5R, “Guide for Specifying Underground Shotcrete”
- ACI C-06, “Application and Use of Shotcrete,” 1981
- ACI CCS4, “Shotcrete for the Craftsman”
- ACI CP60, “Shotcrete Nozzleman Craftsman Workbook CP-60”
- ACI SP-14, “Shotcreting”, 1966, 224p.
American Association of State Highway and Transportation Officials (AASHTO)
www.bookstore.transportation.org
- AASHTO-AGC-ARTBA Joint Committee – Task Force 37 Report, “Guide Specifications for Shotcrete Repair of Highway Bridges,” (TF3&-1), 122pp.
- AASHTO-AGC-ARTBA Joint Committee – Task Force 37 Report, “Inspector’s Guide for Shotcrete Repair of Bridges,” December (IGSRB-1) 80 pp.
ASTM International (ASTM)
www.astm.org
- C42/C42M – Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete
- C1116/C1116M – Standard Specification for Fiber-Reinforced Concrete
- C1385/C1385M – Standard Practice for Sampling Materials for Shotcrete
- C1398 – Standard Test Method for The Laboratory Determination of the Time of Setting of Hydraulic-Cement Mortars Containing Additives for Shotcrete by the Use of Gilmore Needles
- C1140 – Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels
- C1141/C1141M – Standard Specification for Admixtures for Shotcrete
- C1436 – Standard Specification for Materials for Shotcrete
- C1480/C1480M – Standard Specification for Packaged, Pre-Blended, Dry, Combined Materials for Use in Wet or Dry Shotcrete Applications
- C1550 – Standard Test Method for Flexural Toughness of Fiber-Reinforced Concrete (Using Centrally Loaded Round Panel)
- C1604/C1604M – Standard Test Method for Obtaining and Testing Drilled Cores of Shotcrete
- C1609/C1609M – Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading)
- STP- 169D – “Significance of Tests and Properties of Concrete and Concrete-Making Materials,” 2006, J. Lamond and J. Pielert Editors – Chapter 53 – “Shotcrete”, John H. Pye, pp 616 – 624.
International Tunneling Association (ITA)
www.ita-aites.org
- Working Group 12 – Shotcrete Use – Publications:
- Report: Shotcrete in Tunneling: Status Report 1991.
- Report: Shotcrete for Rock Support – Guidelines and Recommendations – A compilation 1992.
- Shotcrete for Underground Support: State-of-the-Art Report with Focus on Steel-fibre Reinforcement,1992, 8 pp.
- Shotcrete for Rock Support: A Summary Report on the State-of-the-Art in 15 Countries, 1993, 29 pp.
- Health and Safety in Shotcreting, 1996, 18 pp.
- Sprayed concrete for final linings: ITA Working Group Report, 2001, 14 pp.
- Lining of Tunnels under Groundwater Pressure, 2002, 6 pp.
- Shotcrete and Waterproofing for operational tunnels, 2005.
- Shotcrete for rock support: a summary report on the state of the art
American Society of Civil Engineers (ASCE)
www.asce.org
- Conference Proceedings
Note: Some Proceedings are out of print, however individual papers may be available. - Use of Shotcrete for Underground Structural Support, Engineering Foundation Conference, South Berwick, ME, Jul 16-20,1974, 467 pp. (Also see ACI SP-45) Shotcrete for Ground Support, Engineering Foundation Conference, Easton, MD, Oct 4-8, 1976, 763 pp. (see ACI SP-54)
- Shotcrete for Underground Support V, Engineering Foundation Conference, Uppsala, Sweden, Jun 3-7, 1990, J. Sharp and T. Franzen Editors, 560 pp.
- Shotcrete for Underground Support VI, Engineering Foundation Conference, Niagara-on-the-Lake, ON, May 2-6, 1993, D. Wood and D. Morgan Editors, 198 pp.
- Shotcrete for Underground Support VII, Engineering Foundation Conference, Telfs, Austria, Jun 11-15, 1995, H. Kdapperich, R. Pöttler and J. Willocq Editors, 313 pp.
- Shotcrete for Underground Support VIII, United Engineering Foundation Conference, São Paulo, Brazil, Apr 11-15, 1999, T. Celestino and H. Parker Editors, 349 pp.
- Shotcrete for Underground Support X, Engineering Conferences International Conference, Whistler, Canada, Sep 12-16, 2006, D. Morgan and H. Parker Editors, 382 pp.
- Shotcrete for Underground Support XI, June 7-10, 2009 – Davos, Switzerland, Editors:Felix Amberg, M.o.S. ETHZ, SIA, Switzerland, Knut F Garshol, BASF Construction Chemicals, LLF, USA
- Shotcrete for Underground Support XII, October, 2015, Singapore. Professor Ming Lu, Nanyang Technological University Dr. Oskar Sigl, Geoconsult Asia Singapor PTE Ltd, Dr. Guojun Li, Singapore Metro Consulting Eds.
- Shotcrete for Underground Support XIII, September 3-6, 2017. Kloster Irsee (near Augsburg), Irsee, Germany (Conference Proceedings will be available later), Professor Dr.-Ing. Dietmar Mähner, Institute for Underground Construction, FH Münster, Germany
Norwegian Concrete Association (NB)
www.betong.net
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support,” Proceedings, International Symposium on Sprayed Concrete, Fagernes, Norway, Oct 1993, R. Kompen, O Opsahl and K Berg Editors, 464 pp.
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support,” Proceedings, Second International Symposium on Sprayed Concrete, Gol, Norway, Sep 23-26, 1996, 433 pp.
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support,” Proceedings, Third International Symposium on Sprayed Concrete, Gol, Norway, Sep 26-29, 1999, 525 pp.
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support, Proceedings, Fourth International Symposium on Sprayed Concrete, Davos, Switzerland, Sep 22-26, 2002, 365 pp.
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support, Proceedings, Fifth International Symposium on Sprayed Concrete, Lillehammer, Norway, Apr 21-24, 2008, 346 pp.
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support, Proceedings, 7th International Symposium on Sprayed Concrete, Sandefjord, Norway, June 16-19, 2014, 458 pp.
- “Sprayed Concrete: Modern use of wet mix sprayed concrete for underground support, Proceedings, 6th International Symposium on Sprayed Concrete, Tromsø, Norway, September 12-15, 2014, 426 pp
Other Volumes
- “Shotcrete: A Compilation of Papers by Dudley R. ‘Rusty’ Morgan,” American Shotcrete Association, Farmington Hills, MI, 2008, 424 pp. shotcrete.org
- “Tunneling is an Art,” Marc Vandewalle, N.V. Bekaert, S.A., Zwevegem, Belgium, 2005, 400 pp.
- “Recommended Practice – Shotcreting in Australia,” Concrete Institute of Australia / Australian Shotcrete Society, May 2008, 67 pp.
- “Shotcrete: Engineering Developments,” Proceedings, International Conference on Engineering Developments in Shotcrete, Hobart, Tasmania, Australia, Apr 2-4, 2001, E. Stefan Bernard Editor, 268 pp.
- “Shotcrete: More Engineering Developments,” Proceedings, Second International Conference on Engineering Developments in Shotcrete, Cairns, Queensland, Australia, Oct 4, 2004, E. Stefan Bernard Editor, 291 pp.