Gunite (Shotcrete Mantles)

Gunite or Shotcrete or Sprayed concrete concerns concrete of high resistance, which is implemented on the structure with a high pressure ejection. It usually contains increased cement content (compared to the injective concretes) and aggregates of small gradation. After its ejection from a nozzle, concrete is firstly applied onto a surface in order to form a concrete layer. Then the sprayed concrete, after the ejection, is coated and becomes flattened, so as to provide a final flat surface where needed. The way concrete is ejected is the most important factor for the proper completion of the project. This method is mainly used to enhance especially the most serious damage of the structural elements of a building, such as columns, beams, sheets, foundations, walls, bearing walls, masonry, etc. There are two methods for shotcrete’s production, the dry and the wet process. In both methods, the mixture is transferred by elastic hoses with the help of an air- compressor until the intervention point.

• Dry method: the mixture is prepared in the construction site, where the dry ingredients of concrete (cement, aggregates) are mixed and put into the blasting machine and after water is added the mixture is ready to exit the nozzle.
• Wet method: after the mixture gets prepared by a concrete production plant, comes ready in the construction site, containing all the necessary ingredients (cement, aggregates, water). After that, the mixture is plumbed into the liquid gunite machine and directly is ejected. This method presents more advantages over the dry one, as the product’s quality remains stable and high, while the losses are minimized.

Advantages:

• It may be ejected even on vertical surfaces or surfaces with of slopes
• The same satisfying result is achieved, only with smaller layers’ thickness compared to cast concrete
• Better adjustment and adherence to the already existing concrete is achieved due to the high pressure of the ejection
• Due to the low rate of water / cement, it has high amounts of resistance
• No formwork is needed