The ASA Outstanding Shotcrete Project Awards Program exists to recognize excellence and innovation on projects in which the application of shotcrete has played a significant role.
ASA’s Annual Outstanding Shotcrete Project Awards Program provides an exciting real-world demonstration of the exceptional advantages of placing concrete via the shotcrete process. Many sustainability advantages are also inherent in the shotcrete process and play a significant role in winning projects as well as the project owner’s ultimate decision to use shotcrete as the method of concrete placement. Projects must be completed between January 1, 2021, through September 1, 2023, and can be submitted in the following areas: Architecture │ New Construction, Infrastructure, International Projects, Pool & Recreational, Rehabilitation & Repair, Underground.
To assist in your submission, we have provided submission resources to inform you of the submission guidelines, a list of questions, and a copy of the owner release form. Please email any questions to [email protected].
In September 2021, American Concrete Restorations Inc. was contracted to perform 60 yd³ (46 m³) of concrete repairs to an existing shaft that is used to access an underground tunnel system in a southern suburb of Chicago, IL. The job was for the Metropolitan Water Reclamation District of Greater Chicago, Thornton Construction Shaft. The dimensions of the shaft are 250 ft (76 m) deep and 30 ft (9 m) in diameter, and the only access is from the top using a crane basket. The project specifications called for the use of a polymer-modified, bagged product using the formand-pour method to replace the old concrete.
During the summer of 1970, on my 18th birthday, my father woke me up and told me they needed me on a job. I drove out that morning in July to the Crucible Specialty Steel plant in Midland, PA. It was my first experience working on a Gunite job. We were gunning refractory in a vessel, and I was throwing 100 lb (46 kg) bags of pre-packaged refractory into a paddle mixer to pre-dampen the material. We emptied the paddle mixer on sheets of plywood and shoveled the pre-dampened refractory material into the dry-mix shotcrete gun’s hopper. The Jetcreter was a continuous-feed gun, and it was tough for us to keep up with it. It was a very long day for me because it took 15 hours to complete the gunning. I left the house that morning in the dark and returned home in the dark. That was my introduction to “Gunite” (now referred to as dry-mix shotcrete).
Como miembro de la Sociedad de Honor Internacional en Economía y con una doble licenciatura en Finanzas y Banca, ingresé al mundo del shotcrete preparado de manera un poco diferente que la mayoría de los que ingresan a esta industria. Eso fue hace más de 20 años, pero los principios de comprender el tiempo, el valor del dinero y los costos de oportunidad están indeleblemente grabados en mi psique. En la actualidad, junto con mi socio comercial, quien también proviene de un entorno de fabricación y negocios en un campo internacional, dirigimos una empresa de transporte, una empresa de concreto lanzado vía seca, una empresa de PebbleTec y una empresa de diseño, todo bajo un mismo techo. En conjunto, tenemos entre 55 y 60 empleados en cualquier día dado. En un negocio de este tamaño, la productividad y la comprensión de los costos laborales son clave para sobrevivir.
In recent years, shotcrete has been widely used for ground support in civil tunnels and mines in North America. Shotcrete technologies have advanced with robust robotic sprayers, high-performance shotcrete mixture designs, and high-performance fiber reinforcement in conjunction with rigorous qualification of shotcrete nozzlemen and QC inspection and testing programs. Design engineers and contractors are using shotcrete more and more often for various underground applications including ground support and final linings in tunnels in soft ground and hard rock mines, as well as in repair and rehabilitation projects in railway tunnels and other underground openings. Large underground caverns have been constructed using shotcrete as the initial liner in San Francisco and Los Angeles, and for both the initial liner and final liner in New York and Washington D.C. This article focuses on recent underground shotcrete technology developments from project experience and provides lessons learned. It also demonstrates that proper quality control and shotcrete qualification programs are critical for successful shotcrete projects.
As a member of the International Honor Society in Economics and with a double BS in Finance and Banking, I came into the world of shotcrete prepared a little differently than most entrants to the field. That was over 20 years ago, but the principles of understanding Time, the Value of Money, and Opportunity Costs are indelibly ingrained into my psyche.
Shotcrete is often the best alternative when repair and restoration are being contemplated and can be the ideal application method for both reinforced and nonreinforced construction. From tanks and pools to chemical and automotive to retaining walls and highway structures, the opportunities are endless.
The shotcrete process has also been used for repair and installation of new linings in industrial melting and firing facilities since 1915. The relining of blast furnaces, ladles, and casting facilities, as well as petroleum and cement producing plants, are some of the applications that employ both wet and dry process shotcreting of specialty, heat-resistant materials. The shotcrete process allows for new installations during downtime and “hot” installation of certain materials as a routine part of the production cycle—another advantage of this unique concrete construction method.
Proper surface preparation allows the shotcrete professional to be able to integrate new materials with in-place construction to form a composite that will stand up to exposure and use. As important as the materials are the coordination of efforts from a properly qualified contractor, materials supplier, engineer, and architect. When all of these pieces are in place, the exceptional benefits of the shotcrete process are realized.
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.
Shotcrete is a placement method for concrete. With proper equipment and placement techniques, concrete shotcreted in place will have strength, unit weight, permeability, and other hardened properties equivalent or superior to cast concrete consolidated by vibration. Due to delivering concrete material through relatively small diameter lines (1.5 to 2 in.) [38 to 51 mm] concrete mixtures for shotcrete placement typically limit the maximum coarse aggregate size to a nominal 3/8 to ½ in. (9.5 – 13 mm) size.
Thus, answering your specific questions:
We are not aware of any expansion bolt manufacturers tests that used shotcrete placement of concrete for their test samples. However, tests on cast concrete should be equivalent with a given compressive strength and aggregate size/type in the concrete mixture.
We expect that as answered in #1, that the tests run with ACI 355.2 requirements in cast concrete would have similar results when used with shotcrete placement of the concrete mixtures with similar hardened properties.
Also, note that ACI 318-19 directly includes shotcrete as a placement method for structural concrete.
Freeze-thaw deterioration is dependent on the concrete being saturated in multiple freezing/thawing cycles. In an overhead application, where water can’t stand on the surface, the concrete can’t be saturated unless water permeates through from the upper surface. And with good quality concrete in the tunnel, water shouldn’t permeate through, so it should be functionally watertight. As a result, freeze-thaw likely isn’t a critical durability issue.
A steel trowel finish does require extra working of the surface and would require the contractor to be very attentive to the proper time to obtain the finish yet not overly disturb the fresh concrete. Gravity is working against the overhead concrete staying in place.
Having a smooth steel trowel finish would make minor shrinkage cracks more noticeable. However, in the tunnel without exposure to sunlight or much wind exposure, and with proper attention to curing, perhaps surface cracking will be minimal.
