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.
Uses of shotcrete
Main application (90%)
Tunneling – Stability
Mining operation – Rock bursting
Hydropower project – Lining
Slope stabilization – Fractured rocked
Other application (10%)
Building Foundation – Stability
Canal lining – Slope stabilization, lining
Fire and corrosion protection – Structure protection
Repair – Structural concrete repair
Swimming pool – Slope stabilization
Shotcrete Mix Design
Shotcrete mix design is governed by same princiles that govern concrete mix design. The major difference is maximal particle sizes. There are some factors need to take in account:
- The cementitious materials are between 20 to 25% of aggregate.
- The water per cement ratio (W/C) ranges from 0.38 to 0.48.
- Aggregate that bigger than 8mm should not exceed 10%
- 95% of the total surface of the aggregate come from sand, Usually sand content from 55%-65% of total aggregate (depend on grading analysis)
- Using of admixtures: superplasticizers
- Using of accelerator
It must be underlined that shotcrete applications have gained much more importance during thr past years due to its flexibility, speediness and economy. This owning to an improvement in the field of application technology as well as concrete technology.