Concrete shotcreting

Shotcreting concrete is a flexible method that’s becoming more and more common in construction projects of all kinds. It entails sprinkling concrete onto a surface quickly, which enables strong adhesion and effective coverage even on curved or vertical surfaces.

Building retaining walls, reinforcing structures, and even crafting decorative elements like fake rocks for landscaping can all be accomplished with this technique. This method works quickly and economically, and it can be used in places where conventional pouring techniques would be impractical or impossible.

Knowing the fundamentals of concrete shotcreting can change the game when working on new construction projects or strengthening existing ones. This article will examine the operation of this method, its advantages, and typical applications.

What is shotcreting?

Shotcreting means layer-by-layer spraying of cement mortars under high pressure. In the process, strong adhesion of the working mixture particles and the treated surface occurs, cracks, voids, and small pores are filled. The resulting shotcrete concrete exhibits the properties of heavy and light grades of cement obtained by traditional methods. Sprayed concrete has a feature: a stronger and more durable structure with high water resistance, frost resistance. With the help of shotcreting, a layer with any structure is formed on concrete. With the help of additives and fillers, the properties of the material vary. For example, you can get a surface with increased fire resistance, thermal conductivity, or resistance to temperature changes.

Types of process

Two methods are used to apply spraying:

1. Dry method.
2. Wet process.

The tasks at hand, the installation type, and the conditions for mixing the mixture will all influence which type is selected.

Dry concreting

Dry cement is mixed with different fillers and used in the dry concrete spraying process. In this instance, a hose is used to supply water under pressure. Within a spray device, the two phases are combined. There, too, a solution with the necessary density forms. There are benefits and drawbacks to the approach.

• ease of use and cleaning of the unit;
• variability of the feed distance;
• the thickness of the resulting layer is up to 6 cm;
• no need to prime the treated surface;
• high interlayer adhesion rates;
• high efficiency.

• no mistakes are allowed when mixing the components of the mixture;
• experience in shotcreting is required;
• difficulties when working with dry material (particles bounce off the surface during application);
• dustiness and increased contamination of the work area.

Wet method

A solution that has been previously prepared is fed into the nozzle when wet spraying concrete. Specialized hoses feed it into a smooth flow under the pressure produced by the concrete pump.

Among the method’s benefits are:

• high homogeneity of the solution;
• easy to work with the finished material;
• no strong dustiness of the area;
• possibility of use in closed spaces;
• remaining materials are used for other works;
• no need for additional processing of the concrete layer, grouting is enough.

Among the drawbacks are:

• small layer thickness – up to 3 cm;
• spraying time;
• difficulty in cleaning the unit;
• inability to maneuver due to short feed hoses.

Shotcreting is a technique for applying concrete that entails spraying it onto surfaces quickly and efficiently. This works particularly well in areas that require additional reinforcement or are difficult to reach. This method is a flexible option for contemporary construction projects because it is perfect for producing long-lasting, smooth finishes on slopes, retaining walls, and tunnels.

Installation

Shotcrete cementing is done with specialized equipment:

• concrete mixer;
• concrete pump or compressor;
• hose, sleeves, sprayer with nozzles.

Technology

There are three steps in the spraying process.

Preparation of the mixture or solution

Depending on the surface’s operational requirements, the cement to sand ratio varies. This ratio is one to three when using mechanical shotcrete and one to four when using atmospheric shotcrete. The mixture used to make sprayed concrete has precise ingredient ratios. For mechanical spraying, the proportion of cement to sand is 1:3, and for atmospheric treatment, it is 1: 4.

It’s crucial to properly mix all the ingredients and use the completed solution within three hours to get a high-quality coating. If not, the concrete will solidify, lumps will appear, and the final surface’s quality will suffer. A plasticizer is frequently added to the mixture of shotcrete. In this case, there are two things to consider:

• a liquid additive is added to the solution only after it has been pre-diluted with water;
• a dry composition is pre-mixed with dry concrete and sand.

Cleaning the working surface

The base in front of Torkretic Cementing is cleared of plaster, paint residue, dust, dirt, and butter. Hydrodynamic, waterjet, or sandblasting techniques work well for this. Iron fittings that have rust on them need to have it removed. Uniform roughness of the working plane is permitted in order to improve adhesion. To lessen the chance of concrete rebound, the cracks should be sealed. Rarefied air should be used to blow the working plane, and a water jet set to 0.3 MPa pressure should be used to wash it.

Beacons are advised for more consistent spraying. It is permissible to reinforce the shotcrete layer using a mesh whose cells have a size of 10 cm. The first ball of shotcrete needs to be applied to the mesh if the cell size of the reinforcing material is smaller.

Sputtering

The shotcrete is sprayed one layer at a time. The layers range in thickness from 0.5 to 0.7 cm. The type of solution, the treated plane’s location, and the concrete application technique all affect this value. Although it is applied in two layers, a thickness of 0.2–0.5 cm is deemed adequate. A probe or beacons are used to control the height.

The best way to apply concrete is in circular motions, with a 90˚ angle between the nozzle and the plane. When processing deep ruts, cracks, and the area between the surface and the reinforcement mesh, a small departure from this value is allowed. The layers should be arranged in 100-cm-deep horizontal strips that are indented from the surface. Processing the joint lines with adjacent strips that overlap by 20 cm should be done all at once.

Applying the second layer after two hours is necessary when using pure cement mixtures without additives. Because there is less particle rebound in this instance, it is acceptable to shorten the distance to the surface to 80 cm. When processing a horizontal structure with a liquid mixture containing plasticizers, the first layer’s drying time is shortened to 20 minutes, and for ceiling applications, it is 40 minutes. Before it sets, the resultant rebound needs to be taken out right away.

As long as it’s warmer outside than 5 ˚C, the completed shotcrete coating needs to be moistened every day for a week. As soon as the job is finished or during downtime, the equipment needs to be thoroughly cleaned with water and dried with air to eliminate any remaining concrete residue.

Shotcreting rules

It’s crucial to adhere to several additional guidelines in addition to the ones regarding shotcrete mixture preparation and surface preparation.

1. Correct use of the unit allows you to achieve maximum savings in materials, high productivity and quality of the work performed.
2. Strictly maintain the distance from the working surface to the spray nozzle and the feed rate of the mixture.
3. Observe the proportions of cement and water, since if there is not enough moisture, the material will clump, and if there is too much, the surface will "float".
4. A high-quality spray is achieved at a pressure in the installation of 0.45-0.50 MPa for a spray speed of 150-175 m/s.
5. To minimize rebound, the solution jet is directed perpendicular to the surface, treating it with circular movements at a distance of 1.3-1.5 m. Surfactants are added to the mixing water to increase the adhesive ability of the solution.
6. To ensure that the resulting surface is smooth, after spraying the last layer of concrete, it should be smoothed with metal trowels and then reinforced.

Shotcrete concreting of a house

Shotcrete requires three items to be used at home: a gearbox, a compressor, and a "pneumatic shovel," which is a holder with a metal bucket at the end. Using compressed air at 4-6 atmospheres of pressure, the sand-cement mixture is forced onto the surface through a sprayer and shoveled into the shovel. Using the wet method, you can apply concrete with up to 0.6 cm particle size due to the size of the bucket holes.

A layer thickness of 0.5–1.5 cm and a distance of 10-15 cm between the nozzles and the surface are crucial to maintain.

Shotcreting is a flexible method that has shown to be very successful in a range of building endeavors. Its speedy and effective concrete application makes it a useful technique for both new construction and repairs.

Shotcreting offers flexibility and durability whether it is used to create complex shapes, repair damaged structures, or stabilize slopes. This approach is highly adaptable to various settings and requirements, which is why many professionals prefer it.

Shotcreting is capable of producing robust, long-lasting results when the proper supplies and knowledge are used. You can decide when and how to apply this technique in your own projects by being aware of its uses and advantages.

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