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2013SumShotcreteEMag

Sustainability Top Ten Sustainability Benefits 1. Formwork savings of 50 to 100% over conventional of Shotcrete cast-in-place construction. The United States Green Concrete Council’s (USGCC) book, 2. Formwork does not have to be designed for internal The Sustainable Concrete Guide—Applications, includes a pressures. list of the top 10 sustainability benefits of shotcrete in its 3. Complex shapes require very little—if any—formwork. chapter on shotcrete. Over the next 10 issues of Shotcrete 4. Crane and other equipment savings or elimination. magazine, this Sustainability column will elaborate on each 5. Labor savings of at least 50% in repair applications. one of the listed advantages. Previous discussion of advan- 6. New construction speed savings of 33 to 50%. tages from past issues can be viewed on the ASA website at 7. Speed of repair reduces or eliminates downtime. www.shotcrete.org/sustainability. 8. Better bonding to the substrate enhances durability. U.S.GREEN 9. with other processes.Adaptability to repair surfaces that are not cost-effective CONCRETE COUNCIL 10. Ability to access restricted space and difficult-to-reach(see below).areas, including overhead and underground Ability to Access Restricted Space and Difficult-to-Reach Areas, Including Overhead and Underground Apumpable concrete mixtures will help minimize the extent them to specify shotcrete for applications where conventionalcapabilities and limitations of the shotcrete placement process.Understanding these capabilities and limitations will allowccessing the site of a concrete pour can often be one ofthe biggest challenges faced by contractors. Good quality, of the challenge. But, in the case of form-and-pump placement, form-and-pump placement methods are difficult and costly forming crews will still be required to install forms and remove to undertake. them after placement. The extent of the challenges can be magnified when accessing difficult-to-reach locations, such as Dry-Mix Shotcrete Process an elevated bridge structure or a location deep underground in When placing dry-mix shotcrete, the concrete mixture is a mine or tunnel. These challenges can often be minimized pneumatically conveyed through a shotcrete hose or other when shotcrete is the placement method chosen. conveying pipe until it reaches the nozzle, where the water The reduction or elimination of formwork minimizes move- required for hydration is added by the nozzleman. The benefits ment of materials, a key benefit provided by the shotcrete in terms of access are obvious. The distance that a dry concrete process. In difficult-to-access locations, a shotcrete nozzleman mixture can be conveyed is dependent on a number of fac- can place concrete thousands of feet (1000 ft = 300 m) away tors—the most important being volume of air. A minimum of from the material source, and is limited only by the amount of 185 ft3/m (5.25 m3/m) is usually required to convey a dry available air required to move the material for dry-mix applica- shotcrete mixture a distance of 100 ft (30 m), allowing the tions and the pump selection in wet-mix applications. shotcrete nozzleman to access elevated locations such as a When faced with the challenge of difficult access, it is bridge deck or confined spaces such as a sewer pipe, while the important for specifiers to have a strong understanding of the remainder of the crew's material and equipment are staged at 60 Shotcrete • Summer 2013


2013SumShotcreteEMag
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