An introduction to shotcrete
Shotcrete is an excellent technology for stabilization and support of structures in a very quick time and for concrete application without using formwork. Shotcrete is also the interacting combination of human, equipment and materials. Shotcrete is a high-performance material which functions only as well as these “three components of success”. Man, personified in the work of the nozzle man, requires great technical skill and dedication to the job. The operator must be able to rely fully on the machine and the shotcrete material. It is the interaction and quality of these components that finally determines the success of the shotcrete application.
In times of rapidly increasing mobility and limited space, the need for underground infrastructure continues to increase. Shotcrete has an important role in these requirements. This method is economically outstanding and almost unlimited technically, making it obvious answer.
Shotcrete is a single technical term that covers different components of a complete construction technology:
- The sprayed concreting process
- The material shotcrete
- The shotcrete system
These three components define a complete technology which has a long tradition, huge potential for innovation and a great future. The material shotcrete is a concrete mix design that is determined by the the requirements of the application and the specified parameters. As a rule, this means a reduction in the maximum aggregate grading to 8mm or maximum 16mm, an increase in the binder content and the use of special shotcrete additive (accelerator) to control the properties of the material. Shotcrete was used for the first time in nineteen nineties and has been permanently developed and improved over few decades.
There are now two different shotcrete processes:
- dry process shotcrete
- wet process shotcrete
The shotcreting process designates its installation. After production, the concrete is transported by traditional means to the processing equipment. Shotcrete or gunite is fed to the point of use via excess-pressure-resistant sealed tubes of hoses and is sprayed and compacted onto the substrate. The following methods are available for this stage of the shotcreting process:
- the dense-flow process for wet shotcrete
- the thin-flow process for dry shotcrete
- the thin-flow process for wet shotcrete
Before being sprayed, the concrete passes through the nozzle at high speed. The jet is formed and the other relevant constituents of the mix are added, such as water for dry shotcrete, compressed air for the dense-flow process and setting accelerators when required. The prepared shotcrete mix is the projected onto the substrate at high pressure which compacts so powerfully that a fully-compacted concrete structure is formed instantaneously. Depend on the setting acceleration, it can be applied to any elevation, including vertically overhead.
The shotcrete process can be used for many different construction applications. Shotcrete and gunite are used for concrete repairs, tunneling and mining, slope stabilization and even artistic design of buildings. Shotcrete construction has various advantages:
- application to any elevations because shotcrete adheres immediately and bears its own weight
- can be applied on uneven substrates
- good adhesion to the substrate
- totally flexible configuration of the layer thickness on site
- reinforced shotcrete is also possible (mesh/fiber reinforcement)
- rapid load-bearing skin can be achieved without forms (shuttering) or long waiting times
Shotcrete is a very flexible, economic and rapid construction method, but it also requires a high degree of mechanization and skillful specialist workers are essential.
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