Washington State’s Capitol Seismic Upgrade will surely rank as one of the top restoration projects of this decade and shotcrete proved to be essential to its success. As with most complex rehabilitations, many of the hurdles faced arose after the project had begun. The ability of the contractors, engineers, and architects working together to overcome these issues proved once again to be the crucial factor in the success of the project.
Thick Section overhead Repair and Strengthening of a Concrete Pier: A Viable Shotcrete Solution
When considering placement options for thick section overhead concrete repair or strengthening, more often than not, the consideration of a shotcrete solution is overlooked. Historically, shotcrete has suffered from being mainly associated with vertical placements for above ground work. This may be due to the fact that until 1983, silica fume enhanced shotcrete was unheard of in North America; therefore, building up placement lifts overhead of more than a few inches thick using shotcrete was not deemed possible. Additionally, many shotcrete contractors customarily have avoided low production applications where placement volumes are measured in cubic yards per day rather than cubic yards per hour. As a result, most thick overhead concrete sections have been placed via the more common method of forming and pumping.
In general, forming and pumping concrete overhead works adequately. In deep sections the concrete or repair material is pumped through a port or valve on the bottom or lower side of the stout form. In effect, the air inside the form is pushed up and ultimately out of the concrete placement location. In deep section repair, there can be challenges devising a methodology that ensures no air is trapped in the upper sections of prepared areas. Repairs to pile caps may preclude the coring of vent holes down through the top of the deck due to congestion of reinforcing steel. In a form and pump application, the issue of adequate bond to the prepared concrete substrate is also a consideration. Most repair installations require a composite action of new material to existing concrete. Curing, shrinkage, and the presence of bleed water floating on top of the new concrete placement may adversely affect the ultimate bond strength of these installations. The aspect of building forms for repair and strengthening placements, especially around precast piling, can be difï¬cult and extremely time consuming as well.
Careful consideration of the pros and cons of shotcrete placement over a more traditional approach of forming and pumping for thick overhead sections offers compelling technical evidence for pursuing a shotcrete option. The following case
Use of Fiber-Reinforced Shotcrete
As many of you Shotcrete readers know, there have been many articles published here on FRS, and many more where FRS is mentioned. Two articles in the premier issue of Shotcrete in February, 1999, mentioned FRS. I have been keeping a bibliography of Shotcrete articles on FRS and, through Summer 2004, I have over 20 listed. These, of course, are available on the American Shotcrete Association (ASA) website. For example, in an editorial in the May 2000 issue, Mike Ballou says, œSteel Fiber Reinforced Concrete”It is time to ï¬ nd out about it, and in a Spring 2003 Technical Tip, Denis O™Donnell discusses where ï¬ bers should or should not be used in ground support for hard rock mining.
The Setenave Dry Docks Rehabilitation
Sentenave is ageneral designation for a shipyard built in the ninty seventies at the right end of Portugal
Rock Stabilization of Two Historically Sensitive Rock Slopes using Shotcrete
The need to stablize these rock slopes was driven by the construction of the Hudson-Bergen Light Rail Project, which was being extended into Weehawken, NJ. The location of the light rail was along the base of the Palisades in Hoboken and Weehawken. The need to stablize these rock slopes was driven by the construction of the Hudson-Bergen Light Rail Project, which was being extended into Weehawken, NJ. The location of the light rail was along the base of the Palisades in Hoboken and Weehawken.
Silica Fume in Shotcrete
Silica fume is a highly pozzolanic mineral admixture that has been used mainly to improve concrete durability and strength and as portland cement replacement. Silica fume has been used primarily in the United States, Canada, and the Scandinavian countries, but is now finding increasing use elsewhere in the world.
Steep Slope Stabilization with Fiber-Reinforced Shotcrete
For the past 150 years or so, roads have been built through the mountain passes in the western U.S. and Canada. Sometimes these roads led to mines; sometimes they started as logging roads. Some were built for access roads for the railroad. Many were built so that people could drive wagons, stagecoaches, and later, automobiles to their destinations. As time went on, some of these roads were abandoned, while others were turned into highways and scenic byways. These roads can be seen on maps, criss-crossing through mountain passes, valleys, and wherever passage was possible. Many of these roads were constructed along mountain slopes, carved out using the largest equipment available at the time, sometimes by hand work, and sometimes by blasting through rocky areas. Road conditions in some of these areas can change dramatically throughout the year. In the mountains, vast amounts of snow can accumulate during the course of just a few days. Sometimes there are heavy rain storms. There can be snow avalanches and mudslides from the rain and snow. In times of drought, vegetation might dry out and die, leaving slopes exposed to erosion, increasing the probability of avalanches and mudslides. Because of varying climactic conditions, freezing-and-thawing cycles, radical changes in the amount and nature of moisture, steepness of slopes, and other factors, slopes need to be stabilized so that rocks, trees, debris, and other factors not listed do not unearth them-selves and become hazards to all things below them. One of many ways to secure and stabilize highway slopes is by the use of ï¬ber-reinforced shotcrete (FRS), usually along with either rock bolts or some other mechanical device drilled into the rock or slope. This paper provides an overview of why ï¬ber-reinforced shotcrete is an excellent choice in lieu of plain shotcrete reinforced with either welded wire mesh or rebar mats for such slope stabilization work.
Specification of Shotcrete Toughness
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.
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.
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