In 2015, the U.S. Army Corps of Engineering began construction on the Davis Barracks at West Point, NY. The 172 million dollar barracks became a state-of-the-art facility. The new barracks was built to house 650 cadets, three in each room, consisting of 297,392 ft2 (27,629 m2).
The barracks building is located on the side of a mountain, below the cadet chapel, which in of itself is a famous landmark. The site for the barracks posed numerous challenges which included the removal of 285,000 tons (259,000 metric tons) of granite for the building’s foundation. Between 2015 and 2017, during the construction, over
Y Not Try a Double Nozzle System
Although many shotcrete workers “claim” to be capable of placing massive amounts of concrete in a daily shift, or shooting with the pump turned “wide open,” in reality, the nozzleman tends to ultimately be the limiting factor on production speed and daily placement volume. Plain and simple they get tired. Shooting too fast diminishes accuracy and overall quality.
We have a cast-in-place wall with extensive rock pockets and voids from inadequate vibration during casting. One option is to tear down the wall and replace, however we are wondering if shotcrete can be used to repair the deficiencies. If so, what are the recommended procedures to prepare and shotcrete the repairs?
Shotcrete is a great solution to your wall casting issue. In all shotcrete repair to get the best bond you need to:
1. Chip back to sound substrate – all the rock pockets and voids should be chipped out (or you can use hydrodemolition) to sound concrete.
2. If the chipped-out area is deep into the wall, make sure to have the opening at about a 45° angle from the back of the chipped out area to the surface so that the air flow providing shotcrete’s high velocity can escape and not be trapped.
3. Do not feather edge the perimeter of the repaired opening. Provide a ¾ to 1 in. (19 to 25 mm) roughly square shoulder at the perimeter edge. If this is sawcut make sure the sawed surface is roughened before shotcreting.
4. Thoroughly clean the chipped-out area to remove all dust.
5. Bring the entire chipped out area to a saturated surface dry condition.
6. Do NOT use a bonding agent. It will detract from the inherent excellent bond of shotcrete.
7. Use an experienced shotcrete nozzleman (ACI-certified in the vertical orientation for the process being used) with a quality concrete mixture, and proper shotcrete equipment.
8. Make sure the shotcrete finishers are experienced and do not tear or delaminate the shot sections.
9. Protect the freshly shot and finished sections from freezing or extremely hot weather.
10. Cure the shot sections for a minimum of 7 days. A water cure is preferred to a curing membrane. Either wet-mix or dry-mix would be suitable for your project.
The shotcrete contractor you select for the project should recommend the process they are best suited for based on their crew experience and equipment. Appropriate testing for this type of repair may include compression testing of the materials from shotcreted panels (ASTM C1140 Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels, ASTM C1604 Standard Test Method for Obtaining and Testing Drilled Cores of Shotcrete, and ACI 506.2 Specification for Shotcrete), and bond pull-off tests to verify the bond of the shotcreted material to the original substrate. For more guidance on shotcrete and its use in concrete repairs, you may want to review ACI 506R-16 Guide to Shotcrete, as it can give you more detailed information about shotcrete materials, surface preparation, shotcrete crews and placement, testing, protection and curing.
We are working on a design-build project located in southern California of which the perimeter walls of the underground parking structure are planned to be shotcrete. Do you recommend any particular ACI publication that would be applicable to the shotcrete operation or does ASA have their own publications, similar to ACI, that are more appropriate to shotcreting?
ACI Committee 506 is the technical committee responsible for creating and maintaining the ACI documents related to shotcrete. ACI 506R-16 Guide to Shotcrete is an excellent resource for shotcrete information including materials, equipment, crew composition and placing techniques. It is a non-mandatory document that is very descriptive and readable. ACI 506.2-13 (18) Specification for Shotcrete is another excellent resource that has mandatory requirements for the contractor’s shotcrete placements. Additionally, the ACI 318-19 Building Code Requirements for Structural Concrete directly addresses shotcrete for use in buildings.
A past article in Shotcrete magazine describes the additions to cover shotcrete in ACI 319-19: shotcrete.org/wp-content/ uploads/2020/06/2019Fal_HanskatHollandSuprenant.pdf
Another past article dealing with Shotcrete Testing—Who, Why, When, and How can be found on our website here: shotcrete.org/wp-content/uploads/2020/01/2011Sum_Hanskat.pdf
Outstanding Infrastructure Project
Project Name:
Deep Cove Foreshore Development
Location:
British Columbia, Canada
Shotcrete Contractor:
Oceanrock Art Ltd.
Architect/Engineer:
Kontur Geotechnical
Material Supplier/Manufacturer:
Remple Bros Ready Mix
Equipment Manufacturer:
Putzmeister
General Contractor:
Capilano Builders
Project Owner:
Andre & Trudel Kroecher
Honorable Mention Project
Project Name:
Bridle Ridge Subdivision
Location:
British Columbia, Canada
Shotcrete Contractor:
Vancouver Shotcrete and Shoring Inc.
Architect/Engineer:
GeoPacific Consultants
Material Supplier/Manufacturer:
Graeystone Ready Mix Inc
Equipment Manufacturer:
REED Concrete Pumps
General Contractor:
Morningstar Homes, LTD
Project Owner:
Morning Star Homes, LTD
We are working on a large infrastructure project in New York state. We have access and approval issues for a new concrete mixture design. Our understanding is we can specify a Pre-Bagged or Pre-Packaged Shotcrete mix for a wet-mix application. Is this the correct terminology? Are there companies that produce this type of product?
We see both Pre-Bagged and Pre-Packaged terminology used. ASTM C1480 / C1480M – 07(2012) uses the rather unwieldy “Standard Specification for Packaged, Pre-Blended, Dry, Combined Materials for Use in Wet or Dry Shotcrete Application.” Most suppliers of packaged dry concrete materials for shotcrete have formulations designed for wet-mix applications. You can find our corporate members who supply pack-aged materials on our website in the Buyers Guide (shotcrete.org/BuyersGuide), select the Category, “Shotcrete Materials-Mixture Sales” and the Subcategory, “Wet Mix.”
I have a 24 in (600 mm) thick shotcrete wall that will have to be scanned for voids. The project has been struggling to locate a local expert who has the capability to scan this thick of a wall. In addition, this new 24 in thick shotcrete wall was dowelled and made “as one unit” together with an existing 24 inches thick cast in place wall. What technique should I use to get the right proportion?
Shotcrete is a placement method for concrete. Thus, all non-destructive testing (NDT) applicable to concrete walls would be usable on your wall. However, it is difficult to get good results with a scanning system for heavily reinforced concrete walls of your thickness. Impact Echo and Impulse Response are two one-sided techniques that can provide good results for a portion of the 24 in thickness though would likely not be able to scan the entire depth. Ultrasonic Pulse Velocity is a potential if you can access both sides of the wall. For one-sided investigation at greater depth you may be able to use a MIRA system. It is sophisticated tomographic system that says it can test from 50mm to 800mm (32 in) thickness. There are national consulting firms that provide these investigation systems. Each requires a highly trained, experienced operator so be sure to verify the firm can document successful experience with the method.
Shotcrete Incorporated into ACI 318-19 Building Code
Since the shotcrete process originated well over 100 years ago, improvements in materials, equipment, and placement techniques have enabled it to become a well-proven method for structural concrete placement. The efficiency and flexibility of shotcrete have been used to great advantage in sizable structural projects, as the high-velocity impact inherent in the process provides the compaction needed to turn low-slump concrete into freestanding vertical and overhead placements with minimal formwork.
Falls Village Penstock #1 Structural Shotcrete Rehabilitation Project
In early November of 2018, Knowles Industrial Services Corporation (KISC) was issued a contract by First Light Power Resources, Inc. (FLP) to perform a structural shotcrete liner within a steel-riveted penstock at the Falls Village Hydro Electric Plant in Canaan, CT. FLP’s request for bids permitted contractors to provide a design-build approach for a structurally self-sustaining system to be built within the penstock interior. The existing 9 ft (2.7 m) diameter, 360 ft (110 m) long penstock was buried in its entire length on a steep bank and crossed underneath a live highway. Penstock replacement by excavation proved to be too costly, as much of the existing penstock beneath the roadway was encased in reinforced concrete requiring significant demolition and interruption to traffic in this area.