What is Shotcrete?
In the early 1900s, Carl Akeley, a famous hunter, naturalist and professor, devised a novel method of making plaster models of large animals for taxidermy work. He made a wire frame, and with a special gun he devised, sprayed plaster onto the frame by means of compressed air. The principle of Akeley’s method was to hold a supply of dry material in the gun, convey it to the nozzle with compressed air, and wet it with the proper amount of water as it was blown onto the frame. This resulted in strong, thin coatings that would not slump off the frame and eliminated the problem of the plaster setting up before it was fully placed. The equipment then was used to patch deteriorated concrete with a sand and cement mix. The results were excellent and, in 1911, patents and trade names were issued for the “Cement Gun” which is what the equipment was called, and “Gunite,” the material produced by the process. Until the 1960s all shotcrete work was dry-process, using pressure-tank guns. During that
As per the American Concrete Institute (ACI), shotcrete can be defined as a mortar or concrete, pneumatically projected at high velocity through a pressure resistant conveying line onto a surface, where it is compacted on impact. Cement, sand, aggregate, water, additives and admixtures are the components entering in the production of the shotcrete mix. Compared to normal concrete, shotcrete differs mainly from three points: • The maximal size of the aggregate used. • The way to place it. • The mixture of shotcrete can be dry or wet. Regarding terminology we can describe Gunite as sprayed mortar while Shotcrete as a sprayed concrete. By gunite we means a cementitious mixture of which the particles size is limited to 8 mm. For shotcrete we consider the use of aggregates of which the maximal size is 16 mm. However, in the last 10 years there is a tendency to limit the maximal aggregate size to 12 mm. Shotcrete development can be summarized from its start to nowadays as follows: Dry proces
