The addition of fibers to concrete and mortars as reinforcement is not a new concept. The ancient Egyptians used straw to reinforce mud bricks for use in structures like the core walls of the pyramids. During the first century AD, the Romans incorporated horsehair fibers in the construction of structures like the Coliseum to help prevent drying shrinkage cracking of the concrete. In the modern era, the first scientific studies on the use of steel fibers to reinforce concrete date back to the 1960s and 1970s.1,2 The use of steel fiber-reinforced shotcrete (FRS) was first introduced in the 1970s.3 The first documented use of FRS was in 1973 by the U.S. Army Corps of Engineers in a tunnel adit project at the Ryrie Reservoir in Idaho. Soon thereafter it became well recognized that soil and rock excavations could effectively be stabilized with steel FRS and its use and acceptance increased globally. In the mid-1990s, the use of macrosynthetic fibers in shotcrete was developed and has increased with particular success in temporary support in underground mines where large deformation capacity is desired. Since the 1970s, thousands of projects have been successfully completed using fibers as reinforcement, including shotcrete, slabson-ground, composite steel decks, slabs-on-pile, and precast elements.
The Shotcrete Inspector Certification program began out of the need in the industry to have knowledgeable individuals inspecting shotcrete projects. Shotcrete contractors often find themselves having to educate project inspectors on the details needed for quality shotcrete placement. Shotcrete is a superior placement option in many cases, yet unfortunately, the expertise in evaluating the work is often non-existent. Many contractors and specifiers are faced with situations on jobsites where the lack of shotcrete-specific knowledge from the inspector has either limited the use of shotcrete or created potential litigious situations. The industry needs a knowledgeable on-site inspector, not necessarily an expert in contract documents or even a laboratory tester. As is the case with form-and-pour concrete, an inspector who has demonstrated basic shotcrete knowledge will
Shotcrete is a placement method for concrete. Even though the shotcrete process is over 100 years old, it constantly evolves and today, it is a modern, costeffective, and more sustainable method of concrete placement. Those of us who regularly shotcrete a variety of work will at times have inspections and therefore have to work with inspectors. Understanding the inspector’s role as a safeguard or agent for the owner is important. However, we often find dealing with inspectors can be a cumbersome part of our job. Knowing how to do something properly and being able to fully explain the means and methods of a specialized process (shotcrete) to someone who has little to no firsthand experience are two completely different animals
Frequently, shotcrete contractors are required to shoot test panels at the beginning as well as throughout projects. Several tests are performed from these panels; however, compressive strength testing is the most common. This article will primarily address compressive strength testing. At some point, every contractor has missed a required break strength on a core extracted from one of their panels. Frequently, those bad results are not caused by bad material or poor workmanship. They are caused by poor test panel handling and improperly performed test standards. Often, the causes of those bad test results could have been easily avoided. Let’s discuss some of the more common test panel mistakes witnessed in the field
It was early November and I was on top of a mountain, at the halfway point of a project that would take 18 months to complete. This is the moment I got a call to help build a swamp, indoors, for a movie set on the coast. We get all sorts of odd requests, but this was a different kind of strange. Without further ado, I said, “Sure, sounds great, when do you need it?” The studio replied, “By Thanksgiving,” as filming was starting the following week. This sort of answer required a little more digging
In today’s complex urban jobsite, easy sites to build on are diminishing, while available sites are becoming harder to reach. In addition, the remaining sites often require creative solutions to develop. The project 1395 22nd St. is a complex of five apartment buildings built into one of the many hillsides in San Francisco, CA, and is surrounded by existing buildings and adjacent properties. Several of the tallest buildings for the project have one level below grade, one level at grade, and ten stories above grade. As part of the foundation system of the project, horizontal and vertical grade beams were installed along the hillside for the first five stories of the buildings and then anchored into the hillside with prestressed tiebacks. The excavated slope was up to a 1.5:1 slope, making for very difficult access to each of the
In North Carolina, we are quite fond of our local swimming holes. Ask any Tar Heel, and they will assuredly regale you with tales of their childhood spent swinging wildly from ropes and jumping from or sliding down boulders. The swimming hole always held magic for us when we were small, with water that glowed with microscopic fool’s gold, and tiny fish that would nibble at our feet. It was a place where we could run, jump, and splash, all while nature was busily oiling the wheels of our young imaginations. It’s a scene that one North Carolinian couple wished to recreate for their grandchildren, right in their backyard.
The Plymouth Tunnel is a 1020 ft (311 m) sequential excavation method (SEM) tunnel located in Silver Spring, MD, that makes up a portion of the Maryland Transit Authority’s (MTA) Purple Line light rail connecting the existing metro lines around Washington, DC. The Purple Line Transit Constructors (Flour/Lane/Traylor Joint Venture— PLTC) is the Lead Contractor with the Traylor personnel self-performing the excavation and lining work for the Plymouth Tunnel.
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.
The Duck Island Clean Water Facility, located in Lowell, MA, is a 32 million gal./day (120 megaliter/day) activated sludge treatment plant. The facility accepts wastewater from several Massachusetts cities and towns, including the City of Lowell and the towns of Chelmsford, Dracut, Tewksbury, and Tyngsborough. The service area includes approximately 220,000 people. The facility has been in the news for the past decade due to its need for massive repairs
For the Ayla Golf Academy and Clubhouse in Aqaba, Jordan, Oppenheim Architecture took inspiration from the surrounding landscape and Bedouin tradition to deliver a distinctive building that evokes the aelemental beauty of the desert and mountains. The design amakes innovative use of shotcrete to create a continuous
In our lives, we seldomly look back and say, “that was a very cool project.” This is one of those projects because aof the challenges we faced from the start. Poor access, intricate finish, difficulty in formwork, concrete chemistry, and protection of the existing exterior façade were all challenges of the Uber Mission Towers Project.
The 14th annual Carl E. Akeley Award was presented to William Clements and Kevin Robertson, King Packaged Materials Company, for their article, “Compatible Shotcrete Specifications and Repair Materials,” published in Shotcrete magazine, Spring 2019. This article discusses how shotcrete is used for concrete repairs with correct test methods and using the right shotcrete material to provide a long service life.
The ASA President’s Award was established in 2005 to recognize a person or organization that has made exceptional contributions to the shotcrete industry. It is the sole responsibility of the immediate outgoing President of ASA to select the recipient of this award. Since 2006, 13 well-deserving individuals and one organization have been awarded the ASA President’s Award, all of whom dedicated their time and energy to advancing the shotcrete industry
This is Part One of a two-part series on potential causes of problems in concrete and shotcrete.