The "projected concrete" is a concrete transported through a hose and projected pneumatically at high speed on the projected surface, as a construction technique. It is a pulverized concrete that is mixed in a predetermined proportion of cement and aggregates and mixed with (or without) water. The projected concrete process was first used in Pennsylvania, USA. In 1907 by Dr. Akeley. The projected concrete is subjected to placement and compaction at the same time due to the force with which it projects with the nozzle. It can impact any type or form of surface, including vertical and aerial areas.
This technology helps in completing the construction task with great economy in terms of time and investments. Shotcrete technology is introduced to make work immediate and easier, where any alteration can exist or any architectural effect has to be enhanced. The technical properties such as the compressive strength and the modulus of elasticity of the projected concrete show an important influence on the safety of the tunnel, the lining of the canals and the construction of buildings, etc. During the construction period. The Shotcrete is an excellent tool for the stabilization and support of the structure in a very short time and for concrete applications without using molds. Projected concrete or "pulverized concrete" is the interaction of man, machine and concrete. In times of rapid mobility and limited space, the need for underground infrastructure continues to grow.
The projected concrete is a cement-based blend projected pneumatically at high speed on a receiving surface. The material component of the cast concrete is essentially concrete or sometimes mortar, but the projected concrete application process is unique. This process allows good compaction of the concrete without vibration. In comparison with cast concrete, other important advantages of the projected concrete process are related to the reduction of the quantity and the time of installation of the formwork, elimination and associated labor costs, very flexible logistics, very good work safety and good environmental conditions . Today, due to the significant advances that have occurred mainly in the last decades, the projected concrete can be considered an adequate repair material, especially suitable in different situations, where the formwork is not practical or can be reduced or eliminated, where Access to the work area is difficult, where thin layers and / or variable thickness are required and where normal casting techniques can not be used. The drawbacks of conventional cast concrete (only based on cement and aggregate mixtures) are reviewed and high performance cast concrete is presented. These new projected concrete materials are produced by the addition of new generations of chemical additives, supplementary cementitious materials and reinforcing fibers.