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As per ACI 506R, “shotcrete is concrete or mortar conveyed through a hose and pneumatically projected at a high velocity onto a surface”. It is widely used in construction and repair applications due to its cost-effectiveness, sustainability, and adaptability.
The shotcrete process is suitable in restricted construction areas, when the formwork is cost-prohibitive, or in the case when variable thicknesses or thin layers are required. The application of shotcrete requires good coordination between the contractor, engineer, material supplier, and architect.
Shotcrete increases the speed of construction which helps in completing the projects on time. Even though the hardened properties of shotcrete are similar to those of traditional cast-in-place concrete, the shotcrete placement process provides extra advantages, for instance, early strength development and exceptional bond with almost all substrates.
What are the Applications of Shotcrete?
1. Repair and Restoration
Shotcrete is a technique for repairing and restoring deteriorated concrete, steel, or wood structures. While it is economical to repair beams of variable depths, caps, columns, abutments, wingwalls, and underdecks, it may become expensive for repairing a full-thickness of the bridge deck.
In addition, shotcrete is used to repair fire and earthquake damages, strengthen walls, and encase steel structures for fireproofing.
The Oregon city arch bridge, Galveston Island pleasure pier, and Blaine hill viaduct bridge are some of the structures in the United States that have been repaired using shotcrete technology.
2. Ground Support
In combination with various reinforcements and anchors, shotcrete effectively stabilizes earth and rock excavations and supports the ground during mining and tunneling. The shotcrete technique is superior to ground-supporting systems like traditional timber and steel shoring. It offers early ground support after excavation or blasting.
Shotcrete provides the ability to conform to the natural irregular profile of the ground without formwork. It has been successfully utilized in advancements of tunnels through altered, cohesionless, and loose soil. Shotcrete can also be employed as a final lining for underground structures.
3. New Construction
Shotcrete is a preferred technique for constructing new structures like tunnels and slope stabilization. It reduces construction costs by minimizing formwork and constructing straight, curved, and irregular surfaces.
3.1 Pools, Water Features, and Skate Parks
The application of shotcrete is feasible for pools and skate parks with many curves. The flexibility of concrete placement provided by shotcrete enables owners to construct a uniquely shaped pool. Shotcrete pools are economical, watertight, durable, and aesthetically appealing.
3.2 Tanks and Domes
Shotcrete is used to construct watertight, economical, and durable tanks of different sizes to store a variety of liquids, including chilled water, industrial wastes, and wastewater. It has also been used to build domes ranging from small shelters to large vessels spanning 60 m.
3.3 Architectural Buildings and Landscape
Shotcrete has been used for many architectural applications like intricately formed building structures, landscapes, and zooscape. This is because it meets the construction needs of architects, designers, and contractors alike. It can easily be used to construct different curves with varying thicknesses as is required in the construction of architectural buildings and landscapes.
Shotcrete has been used for repairing and placing new linings in industrial firing and melting facilities. Some examples are relining of blast furnaces, casting facilities, and petroleum and cement production plants. The shotcrete technique allows for new installations during downtime.
Top Sustainability Benefits of Shotcrete
- Save formwork by 50-100% compared to traditional cast-in-place construction.
- Formwork does not need to be designed for internal pressure.
- Complex shapes rarely require formwork.
- Reduce or eliminate the need for a crane and other equipment.
- Increase the speed of new construction by 33-50%.
- Eliminate downtime.
- Exhibit excellent bond characteristics with existing substrates and subsequently improves durability.
- Suitable to repair surfaces that are not cost-effective with other repairing processes.
- Able to access restricted areas such as overhead and underground.
As per ACI 506R "shotcrete is defined as concrete or mortar conveyed through a hose and pneumatically projected at a high velocity onto a surface”.
1. Dry shotcrete process (gunite)
2. Wet shotcrete process
Shotcrete contains coarse aggregate with a maximum size of 6.3 mm.
1. Repair and restoration
2. New construction
3. Ground support
4. Architectural concrete
6. Pools and skates
7. Tanks and domes
Shotcrete has been broadly used in construction and repair applications due to its economy, sustainability, and adaptability. The shotcrete process is suitable to construct and repair difficult-to-reach areas like overheads, uniquely-shaped structures, and support naturally irregular profiles of the ground without the need for formworks.