The FMP Blog

How Shotcrete Works and When It’s the Best Choice

  • January 2, 2024

Concrete is a very versatile building material. Its compressive strength and durability are unrivaled.

But conventional concrete has its limitations. That’s why shotcrete was invented. 

What is shotcrete, and what are its applications in the construction industry? Keep reading to find out. 

Contents:

1. What is Shotcrete?

2. The Pros and Cons of Shotcrete

3. Dry vs. Wet Shotcrete Mix

4. How Best to Use Shotcrete

5. Final Thoughts


What is Shotcrete?

Shotcrete is sprayed concrete pneumatically projected through a hose at a high velocity. This is a popular method of applying concrete to vertical, overhead, and complex surfaces.

Shotcrete is made of a concrete mix of cement, silica fumes, blended aggregate, steel fibers, and accelerators — all mixed with water.


The Pros and Cons of Shotcrete

Shotcrete is an ingenious development for creating unconventional concrete structures. However, it does come with a couple of drawbacks.

Let’s dive into the pros of cons of shotcrete.

Pros

The benefits of shotcrete far outweigh the limitations. To prove this, let’s highlight what you can gain from using shotcrete in your construction project. 

Fast Application

Unlike cast-in-place concrete, shotcrete requires no need to build traditional formwork to hold the concrete in place. The shotcrete process uses concrete pumps on site to shoot the cement through a delivery hose onto the desired location. 

This not only saves time by cutting out the need to build and take down formwork, but the entire process is straightforward and efficient.  

Reach 

Shotcrete can be sprayed from a distance of up to hundreds of feet.

Since you don’t have to worry about getting the equipment up close, you can build concrete structures in locations out of reach of traditional concrete equipment. 

Shotcrete can be sprayed up, to the side, down, and even underground. It opens up building opportunities that were once impossible.

Economical

Using shotcrete is economical for several reasons. 

First, there you need less material. Although rebar is still advised for some structures, no wood is required for formwork.

Second, the equipment to construct with shotcrete is cheaper if you buy a mixer/pump combination.  

You can save on labor costs since it only requires one person to operate the machine. Let’s not forget faster application means fewer man hours, too. 

Sustainable

Less framework means less wood, reducing your carbon footprint. 

The sustainability of shotcrete is also increased since it has resistance to mold, worms, and fire. It can even handle high temperatures.

Should shotcrete structures need repair, this is easily done simply by adding more shotcrete, providing a longer life span for the entire design and further improving sustainability. 

Cons

While shotcrete may seem to be without fault, it has some limitations that contractors should consider before beginning this type of project.

Requires Expert Application

As amazing as shotcrete is, the laborers who apply it must be just as amazingly skilled. Improper application of shotcrete can be disastrous.

On top of that, the project must be finished fast, or you risk it drying out and going to waste.

Environmental Factors

Shotcrete is especially sensitive to elements like rain and wind. For this reason, it must be applied in a controlled environment or when weather permits. 


Dry vs. Wet Shotcrete Mix

There are two methods of applying shotcrete: wet and dry. The processes differ slightly, as do the effects.

Dry-Mix Shotcrete

Also known as gunite, dry-mix shotcrete is just as you would expect: dry when placed into the hopper. 

Dry-Mix Process

The process of dry-mix shotcrete is to put cement and wet aggregates directly into the shotcrete sprayer.

There is a separate hose attached to the nozzle that dispenses water. Water is added to the cement at a high velocity as the dry mix reaches the nozzle.

This jetting of water is added to the compressed air to create an even higher compaction of shotcrete to the surface. The amount of water added is controlled by the nozzleman by adjusting the valve on the nozzle.

Pros of Dry-Mix Shotcrete

Gunite can be used on job sites where space is limited and trucks cannot transport premixed concrete to the areas needed. It has a higher bonding and tensile strength, and typically produces less waste than wet-mix shotcrete. 

Cons of Dry-Mix Shotcrete

If the nozzleman doesn’t accurately control the water pressure, the water content can vary, causing a difference in concrete texture throughout the project. 

Dry-mix also produces high dust emissions, which can get messy on your worksite and is more expensive. 

Wet-Mix Shotcrete

This type of shotcrete is made from wet cement, but the equipment and process are similar to that of dry-mix. 

Wet-Mix Process

For wet-mix shotcrete, cement and water are premixed and then added to the shotcreting equipment by truck or another large device. It is then shot through the nozzle by compressed air.

Pros of Wet-Mix Shotcrete

Unlike dry-mix, where the nozzleman controls the water ratio, wet-mix shotcrete has a precise and consistent water content (since the entire concrete batch is premixed). 

Wet-mix creates less rebound, resulting in less waste as well. Additionally, the process is cheaper with easier labor. Admixtures can be applied as necessary.

Cons of Wet-Mix Shotcrete

The compaction of wet-mix shotcrete is less than that of dry-mix, causing it to be weaker. Transporting wet-mix can be troublesome, since the concrete must be moved in a truck and kept in motion to prevent drying out. 


How Best to Use Shotcrete

Following the ACI Guidelines is strongly advised to ensure you correctly apply the shotcrete for a long-lasting and sustainable project. 

Although, in theory, you could use shotcrete for every concrete structure, it is especially beneficial for some in particular. Below are the most common applications of shotcrete to consider for your next commercial project. 

Repairs and Restorations

The nature and method of applying shotcrete make it the perfect concrete to use when reinforcing corroded or damaged concrete structures. It is often helpful to repair fire and earthquake-damaged structures as well. 

One good example is the restoration of a bridge. Shotcrete can be propelled high into the air to reach the undersection of the bridge and stay put. On the other hand, the conventional application of concrete would require a much more extensive process with many factors that could go wrong. 

Shotcrete can also be used to encase steel structures for further fireproofing.

Read more: Benefits of Steel Buildings

Free Form Structures

Free-form structures are beautiful architectural feats. However, the construction of these designs can be challenging. 

Using shotcrete can make a seemingly impossible structure a reality and drastically reduce the time and effort needed to build them. 

Swimming Pools

Swimming Pools

Rectangular pools are easy to construct and can be made offsite and placed into the ground. Although a simple process, the design and look of these pools are also simple and boring.

Shotcrete has made it possible to create a more exciting and unique pool with curves and irregular shapes. 

Skate Parks

Good skate parks have as many curves and hills as possible to allow more opportunities for skaters to practice their moves. Shotcrete is the go-to material for these types of parks due to its ability to make smoothly-curved surfaces. 

Landscaping

For a visually-appealing landscape, shotcrete comes in handy. It can also be used to retain the natural look of a property while adding more stability to the hills. 

Theme Parks

The structural requirements of theme parks frequently include unconventional designs and unique forms. 

Shotcrete can be used to make tunnels, domes, curved structures, and any other idea needed to create a magical place that theme parks so often embody. The rides themselves will typically require specialized structures for support and theatrical design. 

Curved Architecture

Any concrete building with a curved design can be built using shotcrete. 

Curved Retaining Walls

Shotcrete has unmatched abilities to support soil while simultaneously creating a boundary wall. That is why it is a top choice for retaining walls for highways, landscaping, and outdoor theatres. 

Ground Support

Because shotcrete can be applied directly to the soil without formwork, it is handy in soil stabilization.

Various anchors and reinforcements can aid in stabilizing the soil during excavation or mining. Shotcrete is beneficial on sloped or irregular ground surfaces and can provide waterproofing for underground structures. 

Concrete Shells

Shell concrete structures have been around for centuries. These 3D spaces are made from curved slabs or folded plates and can carry a significant load regardless of their minimal thickness. 

There are several ways to create a concrete shell, but shotcrete definitely ranks in the top three methods for cost and convenience. 

Refractory

Repairing or lining industrial facilities is one of the applications of shotcrete that is nearly unmatched by any other method. Blast furnaces for firing or melting materials can be lined with a special material called refractory shotcrete

This blend of cement, aggregates, and bonding agents is able to handle higher temperatures. Casting facilities and those used for petroleum or cement production will require refractory cement to be applied to their furnaces or boilers. 

Underground Construction

Underground Tunnel Construction

Due to the risk of life in underground construction, mechanical shotcrete application has become the go-to for tunneling of any kind. It can even be done remotely using a special machine that dispenses the shotcrete without the need for manual labor. 

Shotcrete can be used not only for soil stabilization during tunneling but also for the final lining of the tunnel itself. Additionally, it can be helpful in the construction and repair of underground tanks, reservoirs, and dams. 


Final Thoughts

Without a doubt, shotcrete is a genius engineering development that has propelled the architectural abilities of the world forward. That being said, we are not finished developing the methods of applying shotcrete for even more engineering advancements. 

If you want to use shotcrete in your commercial project, you will need a skilled team to make it work. 

Contact FMP Construction to discuss the possibilities.

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