What is surface shotcrete

One type of construction technique called surface shotcrete is high-velocity concrete spraying. The ability of this technique to quickly and effectively create a strong, durable layer makes it popular for use in both new construction and repair work. In applications where conventional concrete pouring techniques might not be practical, like tunnels, retaining walls, and swimming pools, shotcrete is especially helpful.

Cement, water, and aggregate are combined at the start of the shotcrete process, and the mixture is pushed through a hose and projected onto the surface using compressed air. There is less need for additional formwork because of the strong adhesion of the concrete due to this high-pressure application. Applying the surface allows for flexibility in design and finish because it can be shaped and smoothed as needed.

Shotcrete’s capacity to produce a smooth, continuous layer of concrete improves structural integrity and lessens the possibility of weak spots or cracks. This is one of the material’s primary benefits. Because of this, it is the best option for strengthening structures and shielding them from the elements. Shotcrete is also renowned for having outstanding bonding properties, which guarantee that the concrete sticks to a variety of substrates, such as steel, brick, and rock.

Shotcrete is prized for its adaptability as well as its structural advantages. Applications for it range from mining and slope stabilization to artistic projects like sculptures and facades for buildings. Because of its versatility, it’s a well-liked option for both residential and commercial projects, providing strong performance and a beautiful appearance.

Features of shotcrete

Spraying produces a robust and long-lasting surface that stands out for its ability to withstand changes in temperature and moisture. When it comes to shotcrete surfaces, you can build a layer on the base that is any thickness and shape you want. For instance, you could apply gunite plaster to the walls or mix a substance with unique plasticizers to make the bases more fire resistant. As a result, the shotcrete method is thought to be the most advanced because it allows you to select the specific ingredients that will enhance certain concrete properties.

For such processing, a mixture of cement, sand, additives, and filler is typically utilized. Which layer of gunite concrete can be sprayed on the exterior depends on the size of the latter’s particles:

• If a fine-grained filler with particles no larger than 10 mm is used, then such a composition is suitable for applying a layer 3-4 cm thick.
• Larger filler granules of about 25 mm in size are suitable for creating thick layers up to 150 mm. Such compositions are called shotcrete.

There are two ways to lay the gunite mixture: wet and dry, along with different fillers.

Wet gunning method

Another name for this technique of applying the solution is pneumatic concreting. Using a ready-made solution that has been thoroughly mixed and represents a single mass is what wet gunning entails. The liquid mixture is sprayed onto the surface after being delivered to the nozzle via a hose. To serve the composition on the sleeve, a concrete pump or pneumatic supercharger is employed.

It is highly convenient to use such processing technology for a number of reasons:

• The concrete solution almost does not bounce off the surface;
• Thanks to the homogeneity of the mixture, it is applied quickly;
• In the process of applying the mixture torque, a minimum amount of dust is formed (therefore this method is suitable for closed rooms);
• After processing, you can perform the finish grout;
• Unused excess concrete can be used for other works.

But there are disadvantages as well:

• The solution is supplied at a fairly low speed, due to which the density of the applied layer is below;
• Thorcretic concrete cannot be applied with a thickness of more than 3 cm.
• In the process of processing surfaces, a torque of installations are used, which strict requirements are presented to the maintenance;
• due to low maneuverability and the impossibility of using longer hoses to feed the mixture, concrete mortar can only be applied directly at the site of concrete production.

Dry shotcrete

A lot of people may be familiar with pneumatic concreting, but not everyone is aware of what dry shotcrete is. Since this method of applying the solution necessitates particular preparation, only experts should undertake dry processing.

The basic procedure for this method is to feed the dry solution into the shotcrete machine’s nozzle first, then add water to it via an additional hose. The mixture is pushed under intense pressure onto the surface in the following step. The solution ejection speed in this scenario can be as high as 170 m/s.

When discussing the benefits of the dry method with a shotcrete gun, the following benefits need to be emphasized:

• mixtures can be fed over long distances;
• layer thickness can be 6 cm.
• the consumption of water used for the solution is reduced;
• due to the high speed of mortar feed, it is possible to significantly increase the adhesion of the first layer and the quality of adhesion of subsequent layers;
• before processing, it is not necessary to apply primer mixtures to the surface.
• the dry method shotcreting equipment does not require maintenance (after using the machine, it is enough to blow out the sleeves with compressed air).

There are drawbacks to this method as well:

• there is a strong rebound of the shotcrete plaster;
• a lot of dust and dirt is formed on the work site;
• the work can only be performed by qualified specialists (the master must constantly check the ratio of water and dry mixtures for shotcreting).

Compressors, mixers, hoses, nozzles, and sophisticated shotcrete units are among the tools used in dry mortar spraying.

There’s no use using this method if you want to "refresh" the look of the walls in your home. However, it is worthwhile to select the dry processing method and get in touch with experts who possess all the required knowledge and tools if, for example, shotcreting is required to strengthen foundations.

Shotcreting technology

If you are doing the spraying yourself, it is advised that you break the task up into three phases.

Prepare the solution

The operational requirements for the surface to be treated must be determined before mixing mixtures for shotcreting. The ratio of cement to sand is one to three if mechanical processing is your plan. In order to use atmospheric shotcreting, the component ratio must be 1:4.

Practical! The amount of rebound particles in the solution will be greatly decreased if surfactants are added.

Subsequently, the solution is supplemented with filler and thoroughly mixed. Next, dilute the mixture with water and stir everything together until you have a homogenous mass. Plasticizers and liquid additives are added to the solution last.

Clean the work surfaces

Walls and other surfaces need to be cleared of paint, plaster, oil, dirt, and dust before shotcreting. Using hydrodynamic equipment or sandblasting is the simplest way to accomplish this.

Additionally, you must smooth out all of the fissures (this will lessen the solution particles’ rebound). It is advised to use water pressure of 0.3 MPa to clean the work area.

One way to guarantee uniform application of the solution is by placing beacons on the surface. It is advised to carry out reinforcement in order to fortify the shotcrete concrete layer even more (using a mesh with a cell size of about 10 cm).

Spray

Layers of the composition are applied to the surface. The type of solution and the filler added to it will determine the thickness of each layer, which can range from 0.5 to 0.7 cm.

When spraying, circular motions are used. Ensure that there is always a 90-degree angle between the sprayer and the plane. Spraying at a pressure between 0.45 and 0.50 MPa is thought to work best, and the solution feed rate should be between 150 and 175 m / s.

A few additional subtleties of the work should also be taken into account:

• The entire area must be covered with mortar at once.
• When processing adjacent strips, the mixture is applied with an overlap of 20 cm.
• If you use concrete mortar without any additives, then the second layer of the composition can be applied only after 2 hours. If the mixture contains plasticizers, then the drying time can be reduced to 20 minutes (for walls) and up to 40 minutes (for the ceiling).
• The solution that will bounce off the surface must be wiped off immediately, otherwise it will harden.
• After spraying the final layer, it is recommended to go over the surface with metal floats. This will give the walls smoothness.

Water must be sprayed on the surface for a week following the application of the solution.

Applying concrete to a variety of surfaces is a flexible and effective technique known as surface shotcrete. This method works well for projects where durability and time are critical because it can be quickly constructed and repaired. It is especially helpful in intricate or asymmetrical structures because it can adhere to both horizontal and vertical surfaces without the need for formwork.

The strength and longevity of surface shotcrete are two of its main benefits. Shotcrete, when properly applied, creates a dense, solid layer that is resistant to deterioration, moisture, and temperature changes. This makes it a great choice for long-term resilient structures like swimming pools, tunnels, and retaining walls.

The versatility of shotcrete’s applications is another advantage. It can be customized to meet the needs of individual projects by being sprayed in layers of differing thickness. This flexibility includes the kinds of materials that can be added to the mixture, allowing the concrete’s characteristics to be changed to suit the needs of the surrounding environment or structure.

In general, shotcrete provides a workable answer to a variety of construction-related problems. Because of its strength, versatility, and ease of use, this technique is highly valued in the construction sector. For both new construction and repairs, surface shotcrete offers a dependable and effective way to get excellent results.

With surface shotcrete, you can create a strong, dense, and long-lasting layer of concrete by quickly spraying a mixture of cement, sand, and water onto surfaces. It’s a very flexible construction method. This technique works well for building new structures, repairing old ones, and forming intricate shapes without the use of conventional formwork. Applications for shotcrete include architectural facades, tunnel linings, and slope stabilization. It is a well-liked option for applications needing both strength and flexibility because of its easy application process, superior adhesion qualities, and capacity to form intricate shapes.

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