Interesting and informative papers are always welcome!

Has your company completed an interesting project, introduced a new service or product, or have other news that the shotcrete industry should know about? Then become an author in Shotcrete magazine.

Deadlines for Submission

Issue
Theme
Deadline
1st Quarter | 2023
Top 25 Articles of ASA – Part II
December 15, 2022
2nd Quarter | 2023
Outstanding Shotcrete Project Awards
February 15, 2023
3rd Quarter | 2023
Productivity
May 15, 2023
4th Quarter | 2023
Recreational Projects
August 15, 2023

About Shotcrete magazine

Shotcrete is a quarterly magazine published by the American Shotcrete Association (ASA) and is designed primarily for promotion of the shotcrete process. Present controlled circulation is approximately 17,000 copies and readership includes engineers, contractors, facility owners, manufacturers, distributors, educators, and public agencies involved in the shotcrete industry across 100 countries.

Topics cover all areas of shotcrete such as buildings, parking structures, bridges, rehabilitation, materials selection, and methods. Each issue has a central theme; however, other topics are also featured in each issue. With rare exceptions, specific product names are not mentioned in articles. The publications committee and an ad-hoc technical advisory group review and approve all material before publication.

ASA encourages you to submit material for the following issue items:

  • Feature articles and Project reports (minimum of four per issue)
  • Sustaining Corporate Member Profile (offered to Sustaining Corporate Members of ASA) – View PDF
  • Corporate Member Profile (offered to Corporate Members of ASA) – View PDF
  • New Products & Processes – View PDF
  • Shotcrete Corner
  • Technical Tip
  • Industry News – View PDF
  • Safety Shooter
  • Pool & Recreational Shotcrete Corner
  • Goin’ Underground
  • Contractors Corner

What to include when submitting materials for a feature article, Shotcrete Corner, or Technical Tip:

  • Article text (average article length is 1500 to 2000 and project report length is 800 to 1000 words)
  • Four or more illustrations preferred (photos, tables, charts, drawing details, etc.)
  • Measurements (including length, weight, volume, area, speed, etc.) must be in U.S. units followed by metric conversion in parentheses
  • Temperature must be in degrees Fahrenheit followed by degrees Celsius in parentheses
  • Full references (if appropriate), properly formatted (see below for link to reference examples)
  • Captions for each illustration
  • Short author biography
  • Author photo (if available)

What to include when submitting materials for New Products & Processes:

  • Article text (average length is 200 to 250 words)
  • One photo illustration

What to include when submitting materials for Sustaining Corporate or Corporate Member Profile:

  • Article text (average length is 500 words, although there is no minimum or maximum)
  • Photo(s) to accompany profile
  • Up to two pages of content
  • Company logo and contact information

What to include when submitting materials for Industry News:

  • Article text (average length is 100 to 250 words, although there is no minimum or maximum)
  • Photo to accompany article

How to submit material:

Please e-mail article text, autobiography text, and caption text as a Microsoft Word document.

High-resolution digital images can be submitted via e-mail or disc. Images should be a minimum of 300 dpi, preferably sized at a minimum of 4 x 6 in. for general photos and at 1-1⁄4 x 1-3⁄4 in. for author photos. Line art should be TIFF, JPEG, or EPS files. Glossy photographic prints and/or 35 mm slides are also accepted, and can be returned if requested. We do not accept color inkjet printouts or color copies of photos. We also do not accept embedded graphics unless they are 300 dpi at 4 x 6 in.

Where to submit material:

Tosha Meadows, Managing Editor

American Shotcrete Association
401 Edgewater Place, Suite 600 | Wakefield, MA 01880

[email protected]
Phone/Fax: (248) 983-1712

Did you know you can order reprints of your article, project report, or company profile?

If your company’s project is featured in an article in Shotcrete, the marketing value of that article can be extended by contracting with our design department to create a professional reprint that can be used to market your company for years to come. Options include reprinting the magazine cover, adding your own advertisements, corporate logos, and contact information. To obtain a quote on reprinting your article, fill out and fax in the Reprint Quote Form.

Please submit a point of contact e-mail address for correspondence and a mailing address to send additional copies of the magazine when submitting this material.

Resources

View back issues for previous articles, Corporate Member Profile, Shotcrete Corner, and Technical Tip
Author’s Reference Example Guide

Position Statements

ASA has produced position statements on the best practices for proper shotcrete placement. To date, position statements have been issued by the ASA Board of Directors, Underground Committee, and Pool & Recreational Shotcrete Committee. These statements have also been published in our trade magazine, Shotcrete.

Board of Direction
Pool & Recreational Shotcrete Committee
Underground Committee

Collected Resources

Specification Resources

Previously published shotcrete articles which provide a summary of reference material of interest to specifiers:

Complimentary Web Sessions
Conference Proceedings
Member Company Technical Resources

*Members, do you have helpful technical information about shotcrete on your website to share with the ASA community? If so, email your link to [email protected] for consideration!

Safety Resources

Industry Resources

American Concrete Institute (ACI) | www.concrete.org
  • ACI PRC 506 – Shotcrete – Guide
  • ACI PRC 506.1 – Fiber-Reinforced Shotcrete – Guide
  • ACI SPEC 506.2 – Specification for Shotcrete
  • ACI PRC 506.4 – Guide for the Evaluation of Shotcrete
  • ACI PRC 506.5 – Specifying Underground Shotcrete – Guide
  • ACI PRC-506.6 – Visual Shotcrete Core Quality Evaluation- TechNote
  • ACI PRC-506.7 – Shotcrete Preconstruction Mockup—TechNote
  • ACI PRC-506.8 – Shotcrete Use in Pool Construction – Guide
  • ACI CCS-4 – Shotcrete for the Craftsman
  • ACI CP-60 – Shotcrete Nozzleman Craftsman Workbook
  • ACI CP-61 – Shotcrete Inspector Reference Package
  • Additional ACI Shotcrete Resources
ASTM International (ASTM) | www.astm.org
  • C42/C42M – Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of
  • Concrete
  • C1385/C1385M – Standard Practice for Sampling Materials for Shotcrete
  • C1140/C1140M – Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels
  • C1141/C1141M – Standard Specification for Admixtures for Shotcrete
  • 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)
International Concrete Repair Institute (ICRI) | www.icri.org
  • 110.1 – Guide Specifications for Structural Concrete Repair
  • 320.1R – Guideline for Selecting Application Methods for the Repair of Concrete Surfaces
  • 320.2R – Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces
  • 320.5R – Pictorial Atlas of Concrete Repair Equipment
American Railway Engineering and Maintenance-of-Way Association (AREMA) | www.arema.org
  • Manual for Railway Engineering – Chapter 8 Concrete
International Tunneling Association (ITA) | www.ita-aites.org
  • Working Group 12 – Sprayed Concrete Use – See WG 12 Publications


Disclaimer Resources on the American Shotcrete Association (ASA)’s website are provided as a service to our readers. ASA assumes no responsibility for errors or omissions as this list is a work in progress.

Technical Questions and Answers Archive

Submit a Question

The ASA Technical Questions and Answers is a free service offered to all users, but primarily intended for engineers, architects, owners and anyone else who may be specifying the shotcrete process and/or has need for a possible answer to a technical question.

User agreement: The answers provided to submitted questions are intended for guidance in planning and executing shotcrete applications. This information is intended only for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations, and who will accept responsibility for the application of the material it contains. The American Shotcrete Association provides this information based on the best knowledge available to them and disclaims any and all responsibility for the information provided. The American Shotcrete Association will not be liable for any loss or damage arising therefrom.

If you are unable to find what you are looking for in the archive, then submit a new technical question.

Submit a Question Search all FAQs

Filter by Shotcrete Type

    I am a TBM Tunnel Engineer from India, and I was looking for information on the applicable compressed air pressure range required for a wet-mix shotcrete application (small shotcrete pump-capacity 7 CU.M/Hr) hand spraying with a 30m hose for a better-compacted mix. I would kindly request you to please send me information on the pressure range to be expected for good quality shotcrete placement of the concrete mix on the rock substrate in NATM Tunneling.

    Wet-mix shotcrete depends on air flow at the nozzle to accelerate the concrete to 60 to 80 mph (100 kph to 130 kph). Most air compressors produce their air flow capacity at 100 to 120 psi (7 to 8.4 kg/cm2) at the compressor. However, depending on the size length and couplings in the air hose, there may significant pressure drops when the air reaches the nozzle. Here’s what ACI 506R-16 Guide to Shotcrete Section 4.4.2 states for wet-mix:

    “The recommended ft3/min (m3/min) needed for the wet-mix process is between 200 to 400 ft3/min (5.7 to 11.3 m3/min) air volume at 100 psi (7 bar). Higher air volume capacities are needed for higher volume and higher-velocity shotcrete applications. If a blowpipe is to be used during the shooting process, more air will be required to run both operations simultaneously. Conducting a test during the preconstruction testing phase using a blowpipe while gunning the wet-mix material will indicate if the air compressor has enough air volume capacity to perform both tasks at the same time. Long, small-diameter lines may not provide sufficient air volume capacity, even with a large air compressor. Test and consider increasing the size of the air line.”

    Though there is no direct guidance for air pressure at the wet-mix nozzle you may consider the guidance for dry-mix air pressure in ACI 506R Section 4.4.1:

    “The operating air volume (ft3/min [m3/min]) drives the material from the gun into the hose, and the air pressure is measured at the material outlet or air inlet on the gun. The operating pressure varies directly with the hose length, the density of the material mixture, the height of the nozzle above the gun, and the number of hose bends. Experience has shown that operating pressures should not be less than 60 psi (4 bar) when 100 ft (30 m) or less of material hose is used, and the pressure should be increased 5 psi (0.34 bar) for each additional 50 ft (15 m) of hose and 5 psi (0.34 bar) for each additional 25 ft (7.5 m) the nozzle is above the gun.”

    The minimum 60 psi (4 bar) necessary for dry-mix could be applied to the wet-mix air supply as the velocity created by the air flow is similar.

    I would like to know the fire rating information on a shotcrete wall, 8 in. thick.

    Shotcrete is simply a placement method for concrete. Thus, fire resistance of any shotcreted concrete section can be evaluated by consulting ACI CODE-216.1- 14(19) Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies. There are many factors that affect the fire resistance so you will need to review the code to establish what’s appropriate for your structure.

    Is there a guide to determining pressure applied to a form during shotcrete placement? I have seen references to 50 lb/ft2 (240 kg/m2) but no backup to this. Is the ACI formwork design guide applicable to shotcrete in some way?

    Since shotcrete is pneumatically placed against a one-sided form there is no liquid concrete pressure against the form. When bench shooting vertical walls the majority of pressure from the high velocity impact is carried by the previously placed concrete as the concrete is stacked. Plus, this pressure is very localized, only affecting a small zone immediately adjacent to the impact area of the material stream. Here is an article on a research project that quantified the force https://shotcrete.org/wp-content/uploads/2020/05/2007Sum_TechnicalTip.pdf

    From the paper conclusion “In normal spraying conditions, wet- and dry-mix shotcretes produced a force on the panel of about 45 and 20 lb (200 and 90 N), respectively. The maximum load recorded is 87 lb (389 N) and it was observed in simulating a water plug.”

    If your shotcrete form is exposed to wind forces before placing shotcrete, you may want to consider the wind pressure that may be expected across the entire form during construction to keep the form intact. This should be much less than the 50 lb/ft2 pressure you mention. ACI formwork design is intended for cast concrete where liquid concrete is contained within a two-sided form and is NOT applicable to shotcrete placement. Some sources show a 60 mi/hr (100 km/ hr) wind exerting about 10 lb/ft2 (50 kg/m2) on a vertical wall.

    What is the efficiency of dry-mix shotcrete? How much is over spray vs. how much sticks to the surface?

    Dry-mix shotcrete may have more rebound (coarse aggregate that bounces off the surface) than wet-mix so it may be considered a little less efficient. However, predampening and the use of special nozzles can increase wetting and reduce rebound which makes the dry-mix efficiency approach wet-mix. Rebound may be estimated as 5 to 15%, with an average of 10% of the weight of the concrete materials. The experience and placing technique of the nozzleman can substantially affect the amount of rebound in either dry-mix or wet-mix. Overspray is much less and may depend on wind conditions and placing techniques. When looking at the overall efficiency of shotcrete placement in a given section, dry-mix materials can be tailored much closer to the actual need while wet-mix may have minimum concrete delivery volume and time constraints that would end up not using all the material delivered. Also, dry-mix has approximately ¼ the production rate of wet-mix, so in high-volume placements, wet-mix may have a natural advantage in productivity.

     

    Is it true that shotcrete compression tests are more accurate and are likely to be higher (better) results? Basically, is there a difference when testing wet-mix shotcrete applied pneumatically as compared to simply being taken directly in cylinders from the batch plant or ready-mix delivery?

    Shotcrete placement provides full consolidation of the concrete by high-velocity impact. Concrete placed into cylinders for testing is consolidated by multiple rodding in three layers. Shotcreting also has some percentage of rebound so the concrete mixture that remains in the panel is more paste-rich than the mixture entering the pump. Thus, shotcrete placement may provide better consolidation, and a more paste-rich in-place mixture resulting in higher compressive strengths. However, shotcrete compressive strength is evaluated by cores extracted from panels. The coring process can create microcracking in the exterior surface of the core and produce slightly lower compressive strength than cylinders that have no damage to the outer surface when removed from the cylinder form and tested. Overall, there doesn’t seem to be a significant difference when evaluating the concrete material’s strength by shotcrete placement or concrete cylinders taken before pumping.

    You could establish a correlation on a specific project by taking cylinders before pumping and then shooting material test panels. Then testing the cylinders and cores from the panel at the same age.

    I was wondering if ASA has any safety meeting/ tailgate presentations on high-pressure shotcrete work. I need to ensure my team knows how to properly disconnect hoses and align proper fitting procedures. Furthermore, do you have any guidance on a repair procedure for the rubber hose?

    We have an ASA document, “Safety Guidelines for Shotcrete,” that addresses shotcrete safety. It is not a job specific safety plan but gives you guidance on the information you may include in your plans. You can find it on our bookstore at https://shotcrete.org/bookstore/?productpage=2. A free copy of the Safety Guidelines is provided to all of our corporate and sustaining members. Membership also provides many other benefits, including discounts on shotcrete nozzleman certification and participation in our committees. We have a committee specifically devoted to Education and Safety for shotcrete that is very active.

    Regarding the repair of the rubber hose, there is no procedure to repair any breaches in the hose itself. A damaged or excessively worn hose should never be used as the pressure that builds when a delivery line plugs during pumping is extremely dangerous. Modern pumps can reach 2000 psi (14 MPa) internal concrete pressure when experiencing a plug and the hose must be capable of carrying that high pressure. The wet-mix shotcrete hose is heavily reinforced, and the couplings are designed for high pressure. Your crew must be sure that all clamps are fully engaged on the heavy-duty couplings, and that safety pins are in place.

    I would like to ask if there are any articles, references, etc, which reference procedures to determine the maturity of the concrete applied via shotcrete? Basically, how to generate the validation curves?

    Shotcrete is a placement method for concrete. Thus, generating the maturity curves would be based on the concrete mixtures. There are several online resources about the maturity method. One that discusses production of the curves is from the Minnesota DOT and available in PDF format at www.dot.state.mn.us/materials/concretedocs/MaturityMethodProcedure.pdf.