Shotcrete 101

The world of concrete is vast and complex. If you’re thinking of using concrete for a building project or renovation, you may come across the term “shotcrete.” It’s commonly used for pool construction as well as overhead and vertical applications.

But what exactly is shotcrete, how does it work and what are its benefits?

What Is Shotcrete?

High velocity + hose application

Shotcrete is a more of a process than a product. Concrete is applied through a hose and onto a surface at a high velocity. It’s commonly used to apply concrete to overhead or vertical surfaces, but it can be used for other purposes as well.

The process was invented by Carl Akeley, an American taxidermist, in 1907. Carl used this method to repair the façade of Chicago’s Field Columbian Museum. His technique involved blowing the dry material out of the hose using compressed air and then injecting the water as it was released through the nozzle.

The impact of the application process consolidates the concrete on impact, allowing the material to be both placed and compacted at the same time. Steel mesh, rods or fibers are used to reinforce the material.

Shotcrete is highly versatile, and the method can be used to apply concrete to any shape or type of surface.

Today, there are shotcrete machines that control the entire application process, making installation quick and easy.

Shotcrete is commonly used for:

  • Mines
  • Tunnel walls
  • Automobile tunnels
  • Subways

It may also be used to some degree when constructing underground parking structures and high-rise buildings.

How Shotcrete Works

Shotcrete is a simple concept. There are two main methods of application: wet mix and dry mix.

Wet vs. Dry Mix Methods

In most applications, shotcrete describes both dry-mix and wet-mix. However, with pool construction, shotcrete refers to wet mix, and gunite refers to dry mix.

Here’s how each method works:

Wet Mix Method

The wet mix method is exactly what it sounds like – a previously mixed, wet concrete mixture is sprayed from a hose onto the surface. The mixture is pushed through the hose, and at the nozzle, compressed air is introduced to propel the mixture onto the surface.

One advantage of this method is that it produces less waste, dust and rebound compared to the dry mix method.

Large volumes of concrete can be applied at a time and at a faster rate than the dry mix method.

Dry Mix Method

With the dry mix method, all of the dry ingredients are placed into a hopper and moved pneumatically through the hose into the nozzle. A skilled nozzleman controls the water that’s being added to the dry mixture.

When the dry material hits the water, it doesn’t mix completely. Once the mixture hits the surface, the mixing and compacting is complete.

The advantage of using the dry mix method is that the water levels can adjusted in real-time as necessary. This is ideal for vertical and overhead applications that require a more nuanced approach. It’s also the preferred method for repair work when it’s necessary to stop frequently.

Benefits of Using Shotcrete

Shotcrete has a lot of great benefits that make it a popular option in construction. The material is:

  • Watertight
  • Extremely durable
  • Able to prevent cracks
  • Easy to bond with most materials

You can apply a thin coat of shotcrete in key areas. It conforms to abnormal shapes and can be sprayed into tough-to-reach areas. If you need to fill in corners or awkward shapes, use a hose to spray shotcrete into these key areas.

As we mentioned previously, Shotcrete can be used as a wet or dry process. That application option can be further refined with additives.

If additives are put into the mixture, they can further add to the benefits of shotcrete. A few of the most common additives that provide different benefits to the mixture are:

  • Silica fume – Increases the resistance of the material to both chemicals and water. Rebound levels are reduced, and the final product has flexural strength and compression.
  • Accelerators – Fallouts and other production issues can be easily corrected by improving the placement characteristics of shotcrete. Accelerators create thicker applications in a single pass.
  • Fibers – The addition of fibers increases the toughness of a material while also increasing energy absorption and reducing the risk of cracks.

While the benefits of shotcrete are many, there are also sustainability benefits that need to be considered. Shotcrete is highly sustainable and can help lower the costs of projects. A few of the many ways that shotcrete is more sustainable than other products include:

  • Save 50% or more compared to cast-in-place construction
  • Little formwork is necessary when dealing with complex shapes
  • Construction speed savings of 33% or higher
  • Downtime for repairs is less
  • Enhances durability by offering better bonding to improve construction speeds

Man hours required to complete projects are drastically reduced when you choose shotcrete.

When To Use Shotcrete in Residential Homes

Shotcrete is unique in that it can be used in both dry and wet mix processes. Applications are vast, with the method being used in everything from new construction to building repairs and even ground support.

The material is also commonly used in skate parks, pools and even water parks thanks to its ability to conform to any shape and its watertight properties.

Repairs and restoration are faster and easier, and you’ll even find uses for shotcrete in:

  • Refractory
  • Domes
  • Tanks
  • Support
  • Landscape

It’s important to remember that shotcrete’s final product is very similar to conventional concrete. The key difference is the placement process, which allows for shotcrete to offer superior application in hard-to-reach areas.

You’ll also benefit from the material bonding to a variety of substrates, with instant and rapid bonding.

When dealing with curved or thin elements, shotcrete excels where other forms of concrete do not. New construction can also benefit from using this material because it allows for a much faster construction time with fewer man hours necessary and key cost savings.

A lot of builders and homeowners also like that once this material is smoothed, you can create a variety of looks. You can color the shotcrete after or before applying, or you can also make the material look like natural stone.

In the excavation industry, there are multiple uses for the material, including reinforcing the excavations. Stabilization is offered thanks to shotcrete’s ability to adhere to substrates. The area where shotcrete is used can be backfilled after the structure is complete.

When the shotcrete has fully cured, you can add to its integrity by sealing it so that there are no issues with water penetration, insects or other issues.

If the structure does need to be repaired, shotcrete’s spray application allows for top-of-the-line crack repairs that look just as good as the original application.

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