Shotcrete (wet and dry)and gunite areis atwo commonly commonly used terms for substances applied via pressure hoses. Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface. Wet shotcrete contains all of the water when it is discharged into the shotcrete pump. Dry shotcrete (aka gunite) enters the shotcrete machine as a damp mixture of aggregate and cement with the majority of the water added at the nozzle. All sShotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted onto any type or shape of surface, including vertical or overhead areas.
Shotcrete was invented in the early 1900s by American taxidermist, Carl Ankeny, who used it to fill plaster models of animals. He used the method of blowing dry material out of a hose with compressed air, wetting it as it was released. This was later used to patch weak parts in old buildings. In 1911, he was granted a patent for his inventions????? What are you trying to say?, the "cement gun", the equipment used, and "gunite", the material that was produced. Until the 1950s when the wet-mix process was devised, only the dry-mix process was used. In the 1960s, the alternative method for gunning by the dry method was devised with the development of the rotary gun, with an open hopper that could be fed continuously. Shotcrete is also a viable means and method for placing structural concrete.
The nozzleman is the person controlling the nozzle that delivers the concrete to the surface. The nozzle is controlled by hand on small jobs, for example the construction of small swimming pools. On larger work the nozzle is held by mechanical arms and the nozzleman controls the operation by a hand-held remote control.
The dry mix method involves placing the dry ingredients into a hopper and then conveying them pneumatically through a hose to the nozzle. The nozzleman controls the addition of water at the nozzle. The water and the dry mixture is not completely mixed, but is completed as the mixture hits the receiving surface. This requires a skilled nozzleman, especially in the case of thick or heavily reinforced sections. Advantages of the dry mix process are that the water content can be adjusted instantaneously by the nozzleman, allowing more effective placement in overhead and vertical applications without using accelerators. The dry mix process is useful in repair applications when it is necessary to stop frequently, as the dry material is easily discharged from the hose.
Wet-mix shotcrete involves pumping of a previously prepared concrete, typically ready-mixed concrete, to the nozzle. Compressed air is introduced at the nozzle to impel the mixture onto the receiving surface. The wet-gun procedure generally produces less rebound, waste (when material falls to the floor), and dust compared to the dry-mix procedure. The greatest advantage of the wet-mix process is that larger volumes can be placed in less time.
One major advantage a volumetric mixer has is that it can reduce or increase the slump of the mix on demand. Because water is stored separately and not batch at a central location the operator can respond to this application quickly and change the slump of the mix with a simple adjustment of the water flow valve. Not only can the operator change this slump and deliver what is required, they can, upon completion of the pour, move on to their next job site and produce standard concrete without having to return to the plant to change or reload based upon mix design.
Another advantage volumetric mixers enjoy is that many of the gunite and shot crete jobs are performed in confined quarters such as underground mines and tunnels. It can be extremely difficult to reach these with the conventional means of producing concrete. Accessibility, and maneuverability are both issues that cannot be underestimated when serving these markets. and IIt is simply not possible to reach all of these sites with a batch plant or barrel mixer. Volumetric mixers are manufactured not only in different sizes but also different production rates and can meet a wide range of needs.
The size of a volumetric mixer can be most advantageous concerning the shot crete and gunite markets when confronted with these parameters. Most often a standard truck mounted or skid mounted mixer will suffice for a gunite or shot crete project. However, mixers have been mounted on rail cars, special skid designs have been developed, and even new models have been developed to better serve the industry.
Versatility is a key to producing shotecrete and gunite. Having the flexibility to easily change back and forth between these sometimes complex yet confusing applications will allow you to better serve this market.