Shotcrete and Gunite Sprayed Linings

Sprayed Tunnel Linings

Sprayed concrete is a construction technique that sprays concrete into place instead of pouring it into moulds. There are two methods one uses a dry mix and the other a wet mix.

The dry mix method is usually called gunite and was developed in 1895. The dry mix is pumped to the nozzle using compressed air, where a finely atomized spray of water is added to the stream of materials to hydrate the cement.

The wet mix method is called shotcrete. The sand, aggregate, cement, water and chemicals are mixed and then pumped to the nozzle using compressed air.

As the mining industry continues to deal with the challenges of low commodity prices, the sector is looking for innovation for improved efficiency.

From the general focus on lowering operational costs, mining companies are looking for improved safety, technology, and automation to improve productivity and profitability.

The mining sector is interested in new technology innovation in shotcrete. There have been some significant technological advances in cement admixtures within the past few years. The advances have led to improvements in speed, efficiency and cost using shotcrete as the tunnel lining.

The new admixtures are allowing improvement in excavation downtime between shotcrete and the bolting part of the process.

Fibre reinforcement within the shotcrete is also becoming popular as it improves the strength of the shotcrete and can reduce the wall lining thickness and speed up the operation.

Shotcrete V Gunite

Shotcrete and Gunite are names used in the world of sprayed concrete. 

Gunite was developed in 1895. and uses a dry mix concrete pumped to the nozzle with compressed air and water added at the nozzle.

The concept was developed just after world war two. The system is a premixed wet concrete that is pumped to the spray nozzle by compressed air.

With the use of innovative chemical additives, both types of sprayed concrete are very popular.

Mixing and Pumping Machines

The mixing machines pump and spray concrete and come in a hand help version and a robotic version. Both versions are widely used depending on the type of work. Robotic shotcrete machines are used mostly in tunnelling work, and handheld spray machines on stabilizing mountain rock faces, swimming pools, and other basement waterproofing work.

Mixers

The mixers mix sand, cement, water and chemical admixtures. The batched mix is then placed into the shotcrete spraying machine for use.

Fibo Intercon manufactures a shotcrete mixer that can deliver from 10 m3 to 50 m3 of shotcrete concrete per hour.

Polymer Fibres V Steel Fibres

Polymer fibres may not have the same strength as steel fibres, but you can add far more to a mix, giving the polymer fibre an advantage. For example, there is 55,000 fibre per kg, and with 5 to 6 kg per m3 of concrete, this provides the mix with very rich fibre content.

Structural polymer fibres perform better than steel in high deformation zones when there are more rock stresses.

When the surface of the sprayed concrete is under stress, the fibres begin to work. At this time, the fibres are normally exposed. Steel fibres corrode when exposed, where polymer fibres don’t. This is also the case when there are aggressive chemicals in the water table within the strata.

Polymer fibres are more friendly when spraying concrete. They will bend and flex during the spraying process stopping pipes from clogging up.

New Advancements

There are a number of new shotcrete innovations that allow the tunnelling process to become more efficient. They include:

Some products can replace silica fume and other supplementary cementitious materials, and patented synthetic macro fibres are used as a structural substitute to traditional mesh reinforcement or steel fibres. The system also has other new admixtures that enhance productivity during spraying and deliver more robust application performance.

The savings are impressive, with typical installed costs coming in at least 10 per cent lower than alternatives. 

Mining Shotcrete and Grout Mixers

Fibo Intercon mining products are second to none. When looking for reliability, long life and quality shotcrete and grouting plant, look no further.

Fibo has several tunnel and mining shotcrete mixing layouts to suit different mine and tunnel requirements.

The mixing plant is controlled by a state of the art software that ensures concrete quality and efficiency in delivering outstanding productivity.

Learn more about Fibo Intercon shotcrete and grout mixing plant.

Shotcrete Batching Plant Option 2

Shotcrete Batching Plant Option 2