Sprayed concrete is the method by which concrete is sprayed into place, rather than the more conventionally used pouring or placing into formwork. According to the Sprayed Concrete Association other terms used include Gunite, Shot Concrete and Shotcrete.
There are many applications and uses for sprayed concrete. These include curved structures (including shell roofs and domes and tunnel linings) and free-formed structures (such as swimming pools and climbing walls). Applications also include underground construction, retaining walls and piled wall facings. Sprayed concrete is also commonly used to provide fire protection to steelwork and for strengthening and repair works to existing structures.
There are essentially two methods of application: the dry process and the wet process, typically installed by different specialist contractors and equipment. Both use high velocity air to propel.
Dry process sprayed concrete: a predetermined dry mix of cement and aggregate is propelled through a spraying nozzle, where a finely atomised spray of water is added to the stream of materials to hydrate the cement.
Wet process sprayed concrete: uses batched wet concrete pumped through a hose or pipe to a discharge nozzle where high pressure air propels the concrete into position.
Concrete mixes should be specially selected to suit each application. Your third party accredited supplier of ready-mixed concrete will ensure you are provided with the correct concrete for spraying suitable for your requirements, working to EN206: BS 8500 the European and UK standards for concrete.
For more information visit the Sprayed Concrete Association (SCA) website at http://www.sca.org.uk/
CQ Winter 2008
Read 'Venturing into the Cocoon' article on the sprayed concrete at Darwin Centre, Concrete Quarterly, winter 2008.
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