Introduction to Shotcrete

SHOTCRETE

Shotcrete, or sprayed concrete are all terms used to describe concrete or mortar that is delivered via a hose and pneumatically projected at a high velocity onto the surface. Shotcrete is a cement-aggregate-water combination that is often reinforced with traditional steel rods, steel mesh, or fiber.

Shotcreting is carried out with the assistance of a specialized equipment comprised of a mortar cannon or concrete sprayer and a compressor.

We will study about shotcrete, shotcrete techniques, and shotcrete’s benefits and drawbacks.

SHOTCRETE 101

Shotcrete has been shown to be the most effective technique for fabricating curved structures such as domes and tunnels.

The advancement of technology enables improved control of tasks and their completion with increased efficiency in terms of both time and expenditure.

The advantages of shotcrete include the following:

• Due to the fact that shotcrete needs less formwork than traditional concrete, it is more cost effective.
• It needs just a modest amount of room for fabrication and placement.
• Because shotcrete contains a large proportion of cement, it is very durable.
• It is fire and catastrophe resistant, mold and worm resistant, and has a low permeability.
• Additionally, it has a high thermal resistance mass.

SHOTCRETE HAS THE FOLLOWING PROPERTIES:

1. Frost and thawing resistance:

Frost resistance is achieved by including a suitable air-void system into wet-mix shotcrete.

Typically, a mixture containing between 8% and 12% air has an adequate air system.

Although several dry-mix processes have been tested under moderate freezing and thawing conditions, dry-mix shotcretes are more susceptible to cold and thawing issues than wet-mix shotcretes.

This is due to the difficulties of introducing air into the dry-mix shotcrete and establishing an appropriate air-void system.

2. Strength characteristics:

The compressive-flexural strength ratio seems to be comparable to that of ordinary concrete.

Additionally, relationships between water-cement ratio and strength seem to follow the general pattern of greater strength and lower water-cement ratio.

Initial strength may be very high, reaching 8 MPa after five hours and 22 MPa after twenty-four hours.

3. Toughness properties:

Fibers may be added to shotcrete as a consequence of the material showing considerable load-carrying capability after the occurrence of the first fracture.

Stiffness is defined as the relationship between post-crack load capacity and load capacity in the initial crack.

The kind, size, shape, and number of fibers all contribute to the degree to which this performance is achieved.

Density and permeability may be great when proper field procedures are followed.

SHOTCRETE MANUFACTURING PROCESS:

Wet Mixing:

The wet-mix method combines cement, aggregates, mixes, and water before ductile and aerated.

Typically, a concrete truck delivers a wet mix that is pushed via a shotcrete machine.

Wet-mixes are utilized for large-scale installations that are easily accessible to construction vehicles.

The advantages of the wet method include the following:

• There is little or no need for formwork.
• A cost-effective technique of concrete placement.
• Ideal for uneven surface applications, this product enables convenient material handling in difficult-to-reach locations.

Dry Mixing:

In the dry-mix process, cement, aggregate, and additives are combined and then pneumatically delivered via a tube and subsequently through a nozzle’s water ring.

Water is evenly distributed throughout the mixture.

Typically, dry-mixes are utilized for placements of small to medium volume or in areas with restricted vehicle access.

Shotcrete is utilized in instances when formwork is either too expensive or impracticable.

The advantages of the dry process are as follows:

• Simple to start, stop off, and clean.
• On-site material control is provided.
• The nozzle guy has the capability of moving the cannon 1000 feet horizontally or 500 feet vertically.

SHOTCRETE HAS THE FOLLOWING ADVANTAGES:

1. This method requires little or no organization.
2. It is a cost-effective method of pouring concrete.
3. Intended for use on uneven surfaces.
4. It enables simple material handling in difficult-to-reach locations.
5. Additionally, it is simple to start, stop off, and clean.
6. Increases load bearing capability owing to stress redistribution.
7. It has an exceptional resistance to corrosion.

SHOTCRETE’S DISADVANTAGES:

1. Rainwater either washes the cement away from the sandy surface or saturates it, causing sagging or cracking.
2. The material will be separated between the nozzles by a powerful wind; the deposit’s aim is to save energy.
3. This needs highly trained labor and in-depth geotechnical knowledge.
4. Shotcretes that are improperly applied may create a far worse problem than an untreated one.

SHOTCRETE APPLICATIONS:

• It was utilized in tunnels, mines, drainage audits, and exploitation audits to create subterranean holes.
• In rock slopes, stability and support for excavation foundations are provided by rock and soil fixing methods.
• It is used to safeguard channel linings, ensure the safety of bridges, and stabilize debris flows.
• Additionally, it is utilized to restore reinforced concrete structures such as bridges, chemical processing, and agricultural handling.
• Utilized to restore aging maritime structures such as bulkheads, piers, and seas.

Summary:

Shotcrete may be used in lieu of superstructure (unstructured) and substructure maintenance (unstructured). It is an effective method of hand lay-up for vertical and overhead jobs requiring fast set mortar.

Read Also: