Fiber-reinforced shotcrete has become an established material for ground support in tunnelling and mining applications as well as in new construction and infrastructure repair. Designers and speciï¬ers frequently require such shotcrete to maintain some quantiï¬able postcrack strength or toughness. Until the newly published round panel test method (ASTM C 1550-03)1 becomes more widely used, North American designers and speciï¬ers will likely continue to refer to toughness parameters as determined by the beam test method (ASTM C 1018).2 The following sections discuss various toughness parameters associated with this beam test and their signiï¬cance.
Architectural Shotcrete for Residential and Commercial Development
Architectural shotcrete can be used to enhance the environment of almost any type of project, from backyard pool areas and dramatic rock and water entry features to world-class theme parks like Disneyland and Universal Studios. The versatility, strength, and durability of shotcrete can be combined with the natural appearance of rockwork to make a visually pleasing structure in a natural setting.
The use of shotcrete to create natural looking rockwork originated more than three decades ago. One of the earliest uses was in the creation of artiï¬cial boulders for use in museum exhibits in the Southwest. This type of work then evolved into the creation of rock and water features for residential swimming pools to enhance the surrounding hardscape with natural looking, sculpted rock features.
In residential applications, skilled craftsmen work alongside the shotcrete crew while the pool shell is constructed. Depending on the size of the feature, a steel mat is tied into the reinforcing cage of the pool using No. 3 reinforcing bar at 6 in. (15 cm) on center. As the pool is shotcreted, a mound in the rough shape of the feature to be constructed is shot simultaneously. This mound can then be shaped and sculpted by the rock crew until the desired shape and form is achieved. Once that is accomplished, the shotcrete is slick- toweled and then covered with the necessary material used to give the shotcrete a texture similar to natural stone.
Because of the structural characteristics of shotcrete and the natural look of sculpted rock, the project possibilities are endless. This has opened the door to projects incorporating caves, playgrounds, slides, and retaining walls in both residential and commercial settings. As these features become larger and more complex, the structural aspect becomes more signiï¬cant. Structural ledges and overhangs can be con-structed so that water flows over, but can be walked under. Caves can be constructed within the rockwork so that pumping equipment can be housed, protected, and hidden. This type of feature can be constructed by using No. 3 rein-forcing bar at 6 in. (15 cm) on center. A heavy metal lath is placed on the underside of the
Hear, Here…
Construction sites can be very noisy places”kind of like a Rolling Stones concert, but much longer in duration. A lot of the equipment we use on a regular basis in the construction industry can produce sufï¬cient levels of noise to cause hearing loss when a worker is exposed to that noise for extended periods of time. Complicating this loss of hearing is the fact that the loss comes over an extended period of time. A worker who cannot hear may be in more danger on the job site. He also may develop tinnitus (a ringing sound in the ears), increased stress levels, and increased blood pressure. The ability to hear what is happening around us is an important part of working safely.
Noise levels are measured in decibels (dBA). The scale used for measuring decibels is a bit like the scale used to measure earthquakes. The noise at 73 decibels is about 2 times louder than the noise at 70 dBA. The Occupational Safety and Health Administration (OSHA) has developed rules regarding how long a worker can be exposed to noise levels before hearing protection becomes mandatory.
Shotcrete Repair Saves Baltimore Bridges
This Shotcrete Classic was selected for reader interest. While ï¬rst published 23 years ago, most of the dry-mix shotcrete technology described for repair of bridges still remains relevant today. There are a few areas where things have changed. Small line wet-mix shotcrete equipment is now available with suitable start and stop characteristics for small volume wet-mix shotcrete repair of bridges and other structures and is now also widely used for this purpose. Also, with proper surface preparation and the incorporation of silca fume in shotcrete, bonding agents are now seldom used, or needed. Good guidance regarding current recommendations for shotcrete repair of bridges can be found in the AASHTO-AGC-ARTBA Task Force 37 Report œGuide Speciï¬cation for Shotcrete Repair of Highway Bridges, published in 1998 by AASHTO in Washington, DC.
ACI Shotcrete Nozzleman Certification and the American Shotcrete Association
As a member of the American Shotcrete Association (ASA) since its inception, and as a member of the shotcrete industry for even longer, I have been an active participant in the debate over the importance of shotcrete nozzleman certification. For years, very few throughout the industry disagreed with the need for a nozzleman certiï¬cation program. The vehicle by which a certiï¬cation program could be delivered, however, was argued and debated by industry members everywhere!
American Concrete Institute
In 1997, the American Concrete Institute (ACI) established ACI Committee C 660, Shotcrete Nozzleman Certification, with the mandate to develop, maintain, and update programs for use in the certiï¬cation of persons performing as shotcrete nozzleman. As Chair of this committee, it is my pleasure to announce that this certiï¬cation program is now fully operational, and since its launch at the World of Concrete in Las Vegas in 2001, almost 300 nozzlemen throughout North America have been granted certiï¬cation by ACI.
For years, the shotcrete industry has recognized the need for stringent standards with respect to the quality of the shotcrete process. In addition to good quality, well-proportioned shotcrete mixtures and suitable equipment, shotcrete nozzlemen are certainly a key element in this process. ACI Committee C 660 has delivered a credible and thorough program with strict policies, guidelines, and procedures that respond to the demands of our industry. A select group of experienced and acknowledged shotcrete experts have been approved by ACI to act as examiners for the certiï¬cation program. Today, certiï¬cation of a shotcrete nozzleman through this ACI program provides nozzlemen with not only improved knowledge and skills but also with international recognition as craftsmen.
Shotcrete Rebound- How Much is Enough?
Rebound is an essential element in the application of shotcrete. Rebound is deï¬ned as follows: œMainly large aggregate with some sand and cement that bounces or ricochets off the receiving surface and falls on to lower surfaces.1 There is a vital function that is achieved in the rebounding of shotcrete. The secret lies in knowing how much rebound is enough. To paint a mental picture for the reader to understand rebound, consider a baseball. If you take a baseball and dip it into some fresh concrete and pull it out, it will be covered with mortar”a paste consisting of the cement and ï¬ne aggregate and water”that acts as the glue required to create an artiï¬cial rock called œconcrete. If you took this baseball covered with mortar and threw it at a high velocity against a solid block wall at a 90-degree angle to the wall, the ball would strike the surface and bounce off. Because the paste is also in motion at 95 miles per hour and the paste is not securely bonded to the ball, some paste will leave the surface of the baseball, contact the wall, and adhere to the surface. In layman™s terms, it would œsplat onto the wall. The harder the baseball is thrown, the more the paste would leave the surface of the
Architectural Finishes for Retaining Walls
What kind of architectural ï¬nishes are possible with shotcrete? From the most basic natural gun ï¬nish to exotic carved sculptures, from the gray color of regular portland cement concrete to custom-colored and stained mixtures, shotcrete can take on many different types of ï¬nished appearance. Today™s designers are continually challenged to provide quality finishes that ï¬t the surroundings; and in many applications, shotcrete can ï¬ll these needs. Cut and Finish Methods Achievement of an architectural ï¬nish starts with the establishment of the ï¬nal surface plane. Perimeter forms and guide wires are used to
Jefferson Street Bridge: The “Million Dollar Bridge” Listed on the National Register of Historic Places
Dubbed the “million dollar bridge” by town residents, referring to the cost of building the structure in 1921, the Jefferson Street Bridge in Fairmount, WV, is a three-span reinforced concrete arch bridge that crosses the Monongahela River. Listed on the National Register of Historic Places, the bridge was originally designed by The Steel Engineering Company of New York and was dedicated to the town of Fairmont on May 20, 1921. The John F. Casey Company of Pittsburgh completed the original construction.
Having been used by Fairmont residents for more than 70 years, the Jefferson Street Bridge needed restoration work to ensure the continued safety of the structure. The goal of the restoration project was to take down 80% of the structure with only the original arches remaining intact, reconstruct the bridge with new materials, and retain the same appearance as the original 1921 design.
In 1998, the Mosites Construction Company of Pittsburgh began the two-year restoration project. Working with architectural ï¬rm Howard Needles Tammen & Bergendoff (HNTB) of Alexandria, VA; engineering ï¬rm Gannett-Fleming of Pittsburgh; and RCS Consulting of Ripley, WV, Mosites Construction Company had to overcome numerous challenges related to the design and location of the bridge. Before any demolition could be done, precautions were taken to protect a communi-cations ï¬ber optic cable that ran under the south sidewalk of the bridge. Also, to preserve the six original arches, special engineering methods were employed to keep the demolition of other areas of the bridge from harming the arches. To duplicate the original appearance of the structure parapet and light poles, special architectural precast forms were designed.
To help restore the piers and arches, Mosites Construction Company turned to The QUIKRETE® Companies for its high-quality commercial-grade products. Using 6400 m2 (69,000 ft2) of 37.5 mm (1.5 in) thick pneumatically applied QUIKRETE® Gunite MS®, Mosites successfully restored all four sides of the existing arches.
Innovative Shotcrete Application Over Geofoam Structure Supporting Boston’s Central Artery Tunnel
The objective of Boston’s Central Artery/Tunnel (CA/T) Project is to ease the congestion of approximately 190,000 vehicles per day traveling through the city of Boston. This objective is being achieved through the total reconstruction of Interstate Highway I-93 as it passes through the heart of Boston, together with the extension of Interstate I-90 from its terminus at I-93 just south of downtown Boston to Logan International Airport in East Boston. The Artery replaces an elevated six-lane highway that opened in the late 1950s and originally carried approximately 75,000 vehicles per day. The focus of this article is on two transition structures and ramps in the C09C2 Construction Contract: the I-93/I-90 Interchange Ramps and Surface Restoration at Albany Street, where shot-crete facing has been implemented as a facing system for lightweight embankments.
Understanding Wet-Mix Shotcrete: Mix Design, Specifications, and Placement
The purpose of this article is to examine the use of modern wet-mix shotcrete in underground environments. A critical review is provided of aspects such as mixture design, specifications, and placement. More specifically, the intent of this article is to identify the limits of the wet-mix shotcrete process, examine actual mix designs, discuss the various methods of determining (and specifying) the early-age properties of shotcrete (< 1 day), and review shotcrete placement properties, especially pumping the fresh concrete. The presentation treats various subjects taking into account actual field practices as well as the results of on-going research at Laval University, QC, Canada.