Wet-mix shotcrete has been used more and more for structural applications in the past few decades. Recently, wetmix shotcrete was successfully used to construct a mass structural wall with congested reinforcement and minimum dimensions of 1. 0 m in a sewage treatment plant.
Outstanding Infrastructure Project
Project Name:
Eglinton Crosstown LRT Project at Mt Pleasant Station
Location:
Toronto, Canada
Shotcrete Contractor:
Torrent
Architect/Engineer:
SNC-Lavalin
Material Supplier/Manufacturer:
Innocon Ready Mix & Canada Building Materials
Equipment Manufacturer:
REED Concrete Pumps
General Contractor:
Crosslinx Transit Solutions
Project Owner:
Metrolinx & Infrastructures Ontario
Shotcrete Consultant/Quality Inspections:
WSP E&I Canada Ltd.
South Wastewater Treatment Plant
I n early September of 2019, Gulf Coast Underground (GCU) received a call from the City of Baton Rouge and their construction manager, Jacobs Engineering Group (JEG). There was an issue at the South Wastewater Treatment Plant that would require a unique contractor skillset to properly repair. The problem was that the cast-in-place influent structures receiving 65 million gallons (246 ML) of sewer flow daily, were corroding and needed to be repaired quickly
Davis Barracks Sculpted Wall
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.”