Chemistry

What is Gunite



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In the early 1900's an American taxidermist named Carl Akeley decided that he needed an easier, improved and more novel way to stuff his animals. He developed the first "cement gun", a device which uses pressurised air to blow concrete onto (or evidently into) a place which needs to be filled or repaired. "Gunite" is the dry powder which is used in this process. The dry powder is blown down the tube or hosepipe pneumatically by the pressurised air and then mixed with water further down the tube. This mixture is then expelled from the hose at high velocity onto the surface to which it is required.

At first Akeley used the invention for the purpose for which he intended it, to stuff animals for exhibition within the Field Museum of Natural History, Chicago. This was a very basic prototype of the gun, and almost certainly lacked the same power and efficiency that is present in modern cement guns. However, he later refined his invention into some closer to the concrete gun that we know today in order to repair and refurbish parts of the museum structure that had been damaged. Advances have been made in cement gun technology since then however, as gunite has been largely replaced with a new substance "Shotcrete".

Shotcrete is essentially just pre-prepared concrete pumped through the nozzle of a hose at high pressures. The name shotcrete has become a umbrella term for all applications of both gunite and shotcrete and so people often get confused between the two. It has several advantages over the dry-mixed gunite; it is much easier to apply for example and is much less time consuming, two vital points when a business considers which of the two to use. Other advantages include there being less waste and mess produced, both in the form of escaping dust and less rebounding concrete from the point of application.

Gunite however is still used in some instances. This is due to the fact that it offers a lot of control for the controller of the hose, as the concentration of water-dust can be adjusted at the nozzle. Whilst this may seem fairly useless it offers the user more control over the viscosity of the concrete produced. This makes it particularly useful in applications where the texture of the target is uneven or has a very steep gradient. It also a preferable material to implement when the user has to stop and start applying the concrete, as it prevents the otherwise wet concrete setting in the hose.

There are several practical applications of gunite and shotcrete, surprisingly no longer including taxidermy! A prominent example of shotcrete being used is in the construction of swimming pools, in which a layer of concrete has to be evenly spread over the bottom of the swimming pool pit. Shotcrete and gunite are also used when reinforcing cliffs and other natural stone structures that would otherwise prove hazardous if left untended to. The material is perfect for this purpose as it sprays on like a liquid, ensuring that it fills up the loose cracks in the walls etc.

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