Shotcrete Materials – 1. Cement : Rediset cement may be used in place of OPC to achieve a quick set. Accelerators are particularly required when overhead placing is to be done. For the wet mix process, air entraining cement can also be used. Silica fume can be added to the cement.

• If used, about 15 % silica fume by weight of cement can be included.2.
• Aggregates : Nowadays small sized aggregates are also added to shotcrete concrete to increase the thickness in a single operation while making it economical.
• Reduction in cement content upon addition of aggregates makes it economical.

For the construction of light weight structures, lightweight aggregates are used. While using these aggregates, the dry mix method should be followed.3. Water : Potable water should be used. Quality of this potable water for mixing is discussed HERE,4.

• Quick set
• Very early strength
• Compaction
• Adhesion

5. Reinforcing steel : Steel bars with a diameter of more than 16 mm cannot be used practically for shotcreting.

What is the difference between concrete and shotcrete?

What is shotcrete and when is it used? – Q. What is shotcrete and when is it used? A. Shotcrete is a method of applying concrete projected at high velocity primarily on to a vertical or overhead surface. The impact created by the application consolidates the concrete.

• Although the hardened properties of shotcrete are similar to those of conventional cast-in-place concrete, the nature of the placement process results in an excellent bond with most substrates, and rapid or instant capabilities, particularly on complex forms or shapes.
• The shotcrete process requires less formwork and can be more economical than conventionally placed concrete.

Shotcrete is applied using a wet- or dry-mix process. The wet-mix shotcrete process mixes all ingredients, including water, before introduction into the delivery hose. The dry-mix shotcrete process adds water to the mix at the nozzle. Shotcrete is used in new construction and repairs and is suitable for curved and thin elements (ACI 506R).

What is the difference between wet and dry mix shotcrete?

What is shotcrete and when is it used? – Q. What is shotcrete and when is it used? A. Shotcrete is a method of applying concrete projected at high velocity primarily on to a vertical or overhead surface. The impact created by the application consolidates the concrete.

1. Although the hardened properties of shotcrete are similar to those of conventional cast-in-place concrete, the nature of the placement process results in an excellent bond with most substrates, and rapid or instant capabilities, particularly on complex forms or shapes.
2. The shotcrete process requires less formwork and can be more economical than conventionally placed concrete.

Shotcrete is applied using a wet- or dry-mix process. The wet-mix shotcrete process mixes all ingredients, including water, before introduction into the delivery hose. The dry-mix shotcrete process adds water to the mix at the nozzle. Shotcrete is used in new construction and repairs and is suitable for curved and thin elements (ACI 506R).

What is gunite shotcrete?

Shotcrete, gunite, or sprayed concrete is concrete or mortar that is conveyed through a hose and is pneumatically projected at high velocity on the surface. Shotcrete is a mixture of cement, aggregates, and water that is usually reinforced by conventional steel rods, steel mesh, or fiber.

What is shotcreting?

FAQ – What is shotcrete concrete? (Define shotcreting.) Shotcreting meaning can be understood as, Shotcrete is a fine concrete deposited onto the surface pneumatically through jetting at high velocity. What is shotcrete and what are the two methods of shotcreting? Shotcrete is a process of applying the concrete by propelling it from a nozzle with the help of compressed air.

• Cement and sand mixture is prepared and fed to mechanical feeder called gun.
• The gun passes the mixture to the delivery hose by the feed wheel/distributor.
• From the delivery hose, the mixture is passed to the nozzle by compressed air.
• Perforated manifold inside special nozzle sprinkles water forming mortar.
• Mortar is ejected from the nozzle at high velocity to the surface to be shotcreted.

Water content in the mixture can be adjusted by controlling water discharge from the manifold of the nozzle. For wet mix shotcreting, the following application procedure is used:

• Concrete mortar is prepared as usual.
• The mortar is metered into a feeding chamber.
• Then the mortar is passed into the delivery pipeline.
• Then, mortar is passed to the nozzle by compressed air at a speed of 5.5-7 atmosphere.
• Mortar is ejected from the nozzle at high velocity to the surface to be shotcreted.
• High velocity system is established using a small nozzle and high pressure which gives good compaction, but low output.
• Low velocity system is established using large diameter hose which gives high output, compromising compaction.

What is shotcrete rebound? Shotcrete rebound : During the process of shotcreting from the gun, some of the concrete falls off the surface because of the high velocity of the jet. Shotcrete rebound consists of maximum large size particles like aggregates.

Cement content is minimum in the rebound. Shotcrete rebound is maximum at corners and overhead surfaces. It also increases with a decrease in w/c ratio. For vertical wall surfaces, shotcrete rebound is minimum. It can also be minimised by keeping the jet at the right angle to the surface to be shotcreted and keeping the gun at 1 m away from the surface.

Image Courtesy : Schematic representation of Dry Mix Shotcrete, Wire Mesh in Shotcrete, Nozzle for Shotcreting,