Also referred to as sprayed concrete, shotcrete is a multipurpose building material that is becoming more and more well-liked due to its effectiveness and adaptability in a range of construction projects. Shotcrete is applied differently from traditional concrete, which is poured into formwork and allowed to cure, by employing specialized equipment to spray the concrete mix at a high speed onto surfaces.
A carefully measured mixture of cement, aggregates, and water is used to start the process. Admixtures and fibers are examples of additives that are occasionally added to improve particular qualities like strength, durability, or workability. After that, the mixture is fed into a hydraulic or pneumatic pump system, which sends it through a hose and out of a nozzle.
When the concrete mix is sprayed onto the receiving surface, compressed air at the nozzle causes it to accelerate to extremely high speeds. Shotcrete can adapt to many forms and contours thanks to this application technique, which makes it appropriate for intricate geometries like tunnels, slopes, and curved walls. Because shotcrete can be applied overhead, horizontally, or vertically, it is the material of choice in difficult construction situations.
Shotcrete is applied using two main techniques: wet-mix and dry-mix. The components of wet-mix shotcrete are combined with water and then pumped through a hose to be sprayed onto the surface. Uniformity and instant hydration upon contact with the substrate are guaranteed by this method, which can be useful in controlled environments.
However, with dry-mix shotcrete, the dry concrete mix and water are fed into the nozzle separately, where they are mixed and forced onto the surface by compressed air. This approach is frequently preferred for outdoor applications or circumstances where access to water is restricted because it provides more control over the consistency of the mix.
Compared to traditional methods, shotcrete’s rapid application process shortens construction times, which is especially advantageous for projects that need to be completed quickly. Because of its high bond strength and longevity, it can be used in structural applications where resilience and longevity are essential, like tunnel linings, swimming pools, and retaining walls.
Shotcrete continues to be at the forefront of contemporary construction methods as materials and technology progress, providing engineers and builders with a dependable way to achieve both structural integrity and architectural flexibility in their projects.
With its flexible application method, shotcrete—also referred to as sprayed concrete—revolutionizes the construction industry. Using this technology, concrete is projected onto surfaces at a high speed, producing a strong, long-lasting layer that is perfect for tunnels, swimming pools, and structural repairs. Shotcrete adheres to vertical or overhead surfaces without the need for formwork, which makes it quicker and less expensive than traditional concrete pouring. Depending on the requirements of the project, the procedure uses formulations for either a wet or dry mix. Shotcrete is a popular option in contemporary construction because of its versatility, strength, and ease of application. It provides increased strength and efficiency in situations where traditional techniques are insufficient.
- What is shotcrete
- Types of process
- Dry concreting
- Wet method
- Installation
- Technology
- Preparation of the mixture or solution
- Cleaning the working surface
- Spraying
- Shotcreting rules
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What is shotcrete
Concrete shotcrete technology applies concrete mixture to any surface using flexible special lines that are subjected to high pressure. The technique helps to fill all gaps, fissures, and potholes by greatly compacting the solution and increasing its adhesion.
Depending on the technology being utilized, a layer of concrete composition as thick as three to six centimeters may be applied. Using a spraying technique, concrete is produced with a better structure that is stronger, more resistant to moisture, and less susceptible to frost. By varying the volume of cement and fillers, as well as the addition of specific additives to the solution, technical characteristics can be altered.
- Ability to perform work at sub-zero temperatures.
- Increased strength and resistance to mechanical stress.
- Minimal water absorption due to compaction of the solution.
- Resistance to aggressive environments, sudden changes in temperature / humidity.
- Laying without the need for formwork installation.
This technology is employed for a wide range of tasks, most frequently in the construction of structures or monolithic components. Concrete is fed under constant pressure through a special hose on one side while formwork is installed on the other after a steel reinforcement frame is constructed.
Shotcrete is applied in layers, enabling the creation of a thin but sturdy monolithic structure. Complex surfaces (concave, convex, bowls, arches, vertical planes, etc.) can be quickly and affordably created.
The process of repairing structures also benefits from the use of concrete mixtures since they provide a dense and long-lasting filler for chips, cavities, and cracks. The coating greatly strengthens and prolongs the life of the structure, shielding it from any detrimental influences.
- Repair and renovation of finished monolithic concrete structures.
- Strengthening tunnels and monoliths during underground work.
- Soil fastening during excavation work.
- Application of the top layer of concrete, which has increased strength and durability, in order to strengthen structures, buildings.
- Insulation of foundations, ensuring their strength.
- Construction of architectural objects of complex shapes and configurations.
- Creation of fireproof, waterproof, frost-resistant coating.
Types of process
There are two primary technologies available for shotcreting: wet and dry methods. The selection of a particular technique is done while considering the conditions for mixing the mixture, the tasks assigned, the presence of an installation of the necessary kind, etc.d.
Dry concreting
The technology is based on the use of various hoses to supply dry cement mixture and water. Compressors provide compressed air under pressure for both components, which are combined in a specialized sprayer. Subsequently, the mixture is fed out of the nozzle at an average speed of 170 m/s.
- The material is obtained with increased strength and density characteristics.
- The mixture can be fed over long distances, which significantly speeds up the process of work and increases maneuverability.
- Maximum adhesion level.
- Possibility to apply the mixture in a layer up to 6 centimeters.
- Reduced cost of work due to reduced labor intensity and productivity.
- Possibility to turn on/off the unit at any time.
- Ease of operation and cleaning of the unit.
- No need to prime the surface being processed.
- Higher consumption of the mixture due to rebound.
It is important to note some of the method’s drawbacks, including the requirement that the master have shotcreting experience, the elimination of any mistakes in the component mixing process, the challenge of working with dry material, and the increased dustiness and contamination of the work site. The concrete surface needs to be finished after the mixture is applied.
Wet method
When utilizing this technology, the unit’s sprayer is filled with the ready-to-lay solution. A concrete pump or compressor is used to feed the mixture into the solution. If a concrete pump is chosen, the mixture enters the nozzle under constant pressure, guaranteeing that each layer is distributed evenly. However, because the composition is pumped in portions by the pneumatic compressor, more concrete is used.
- The mixture is fed to the sprayer already prepared, which increases the homogeneity and high-quality coating of shotcrete of any design.
- Significant savings in material, reduction in waste volume due to a small rebound.
- The ability to perform finishing immediately after the completion of the last layer.
- The solution that did not get on the surface of the monolith can be used for other work.
- The mixture is sprayed at a minimum distance to the surface, so this method of shotcreting can be used to carry out work in closed rooms.
- Absence of significant dustiness of the room or territory.
- Absence of the need for mandatory additional processing of the concrete layer (grinding is enough).
The layer can only be applied with a maximum thickness of 3 centimeters. The feed rate is low (up to 100 m/s). Spraying takes a long time. The unit is difficult to clean after work is done. Short hoses for feeding the mixture make it difficult to maneuver. There is also no way to stop work, which causes the mixture to harden and equipment failure.
Installation
Shotcreting requires specialized installations, which typically include the following components: a concrete mixer, a concrete pump or compressor, sleeves, hoses, sprayers, and nozzles. Installations for both dry and wet concrete supply are designed based on the shotcreting technique.
Water and dry cement mix are supplied via separate lines in a dry shotcreting installation. The machine works well for long-distance delivery of composition, doesn’t need to be washed, and lets you build a thick layer. Installation kit: includes unit, high-pressure hoses, compressor, and water-tank-designed tank.
Wet shotcreting installations use a concrete pump to supply ready-made cement mortar to the nozzles via a hose. Reduced material consumption is important for indoor use. When compared to the dry method, the coating thickness (maximum indicator) is two times thinner.
The market has a sizable assortment of both domestically and internationally manufactured equipment. Well-known installations of the wet method-using German company PFT. The G4 and G5 series installations come standard with an auxiliary air blower, a mixing gun nozzle, and a control panel.
Should it be required, renting the installation can be done at a significantly reduced cost. The daily rental fee is fixed on an individual basis and ranges from 990 to 3500 rubles. The model, length of rental, amount of deposit, etc. all affect the price.
The dry spraying systems produced by JSC Alpservice (Ukraine) have shown excellent market performance. They are frequently employed for repair work, strengthening tunnels and foundations, and restoring various kinds of hydraulic structures. Building materials are fed by the unit up to a distance of 80 meters.
It is important to consider the way the work is done, volumes, hose length, power, pressure, and other aspects when selecting a shotcrete machine.
Technology
The technology involves various types of mixture preparation and supply, depending on the selected approach. If not, every step of the work stays the same.
Preparation of the mixture or solution
Shotcreting uses a variety of cement-sand mixtures, the proportions of which are determined by the surface’s operational requirements and environmental factors. Use one part cement and four sand for atmospheric shotcreting and one part cement and three sand for mechanical shotcreting. The ingredients must be properly combined and the final solution must be used within three hours in order to produce a coating of the highest caliber.
Stone chips and crushed granite or gravel can also be added as fillers to concrete. The maximum fraction of large particles in a wet application method should be 8 millimeters; in a dry method, filler can be used up to 25 millimeters.
Concrete can be treated with hardening accelerators, plasticizers, etc.D., They make working with the mixture simpler. After adhering it with water, the liquid additive is added to the composition. The dry additive is combined with cement and sand when it’s in its dry form. Micro-targeting elements are occasionally added to concrete to increase its strength.
Cleaning the working surface
Prior to beginning construction, the foundation is meticulously cleared of any materials that may exacerbate concrete adhesion, such as paints, oils, plaster, dust, and other debris. Sandblasting, hydrodynamic, and hydro-carbrane techniques are available. Rust remnants have been eliminated from the reinforcement. Rough surfaces can enhance clutch performance. The working plane is blasted up by sparse air, all the cracks are cleaned, and a water stream at 0.3 MPa of pressure is used to wash it down.
Experts recommend using beacons to spray concrete more evenly; to reinforce the layer, you can reinforce the monolith with a mesh that has 10 centimeter-sized cells. The mesh is closed with the first layer if the cell of the reinforcing material is smaller.
Spraying
Layers of drying using torquebone can range in thickness from 0.5 to 0.7 centimeters. The location of the processed plane, the concrete application technique, and the kind of solution all affect the layer’s thickness. Although it is thought that 0.5 centimeters is sufficient, it is preferable to apply two layers, the height of which can be adjusted using beacons or a probe.
Concrete is sprayed in circular motions, with a 90-degree angle between the nozzle and the plane. When processing deep gaps, potholes, and the space between the reinforcing mesh and the surface, a small deviation is allowed. Every layer needs to be laid out horizontally, with an indentation of 100 centimeters from the surface. Completely cover the area at once, processing the strip junction line with a 20-centimeter drop.
If one is using only pure concrete mixtures without any additives, the second layer is put on after two hours. Applying concrete at a distance of 80 centimeters from the surface is permitted because there will be less particle rebound. When applying a liquid mixture containing plasticizers to horizontal surfaces, the first layer takes 20 minutes to dry, whereas ceilings require 40 minutes.
Before it sets, the rebound is taken out right away. In the event that the air temperature rises above +5 degrees, the completed coating is moistened every day for seven days. The equipment is thoroughly cleaned with water and then blasted with concrete-blasting air during downtime or after the job is finished.
Shotcreting rules
There are some guidelines that must be followed in order to properly cover the surface with shotcrete concrete. Even though the procedure is fairly straightforward, you must at least be aware of each coating step in order to carry it out.
- Familiarization with the operation of the installation is very important: correct operation will save on the mixture, increase productivity and ensure high quality of the coating.
- It is important to strictly observe the distance from the spray nozzle to the work surface, set the optimal speed of the solution supply.
- The proportions of water and cement should also be precise, since with excess moisture the surface will float, with a lack of moisture – the solution will lump.
- To minimize rebound, the stream is directed perpendicular to the surface with circular motions, the distance is 1-1.5 meters.
- High-quality spray is obtained at a pressure of 0.45-0.5 MPa under the condition of a spray speed of 150-175 m / s.
- To obtain a smooth surface after spraying the final layer, the concrete is smoothed with metal floats, then ironed.
Shotcrete (sprayed) concrete | Shotcrete is a method of applying concrete through a hose and nozzle, sprayed onto surfaces at high velocity. It"s used for construction and repair projects where traditional pouring isn"t feasible. |
Concrete shotcrete: what is it, technology | Concrete shotcrete refers to the process of spraying concrete onto surfaces. It involves a mix of cement, aggregate, and water propelled through a hose using compressed air. This technique is versatile, allowing for efficient application on vertical or curved surfaces. |
Shotcrete, sometimes referred to as sprayed concrete, is a flexible and effective way to apply concrete that has many benefits for building projects all over the world. In contrast to conventional concrete placement techniques, which entail pouring concrete into forms, shotcrete entails highly-velocity pneumatic spraying of a mixture of cement, aggregates, and water onto a prepared surface. In addition to expediting the building process, this method improves structural integrity by creating a compacted, dense layer that firmly conforms to any shape or contour.
Shotcrete’s flexibility to different project requirements and environmental conditions is one of its main advantages. Applying it to vertical, horizontal, or overhead surfaces enables it to be used for building tunnels, sculptures, walls, and even swimming pools. The capacity to alter the mix design, including the amount of cement, additives, and aggregate size, guarantees that shotcrete can satisfy the project’s particular requirements for workability, strength, and durability.
From a technological perspective, shotcreting calls for specialized tools like a compressed air delivery system, a concrete pump, and a nozzle that sprays the mix onto the surface. With the help of this equipment, application can be precisely controlled, guaranteeing excellent bonding with the substrate and uniform thickness. Additionally, shotcrete’s quick-setting quality speeds up construction schedules, cutting costs and project timelines overall.
Another reason shotcrete is a sustainable building material of choice is environmental considerations. Minimizing the need for formwork cuts down on wasteful material usage, and faster construction leads to more energy efficiency, which lowers carbon emissions over the course of the project. Furthermore, shotcrete is a long-lasting material that enhances the sustainability and resilience of buildings under a variety of weather conditions and climates.
To sum up, shotcrete is a cutting-edge, versatile, and effective way to use concrete in construction. Because of its technological advancements, it is now the go-to option for projects that prioritize durability, speed, and versatility. Shotcrete is still a key material in the built environment, helping to shape it as construction methods change by providing creative solutions that satisfy environmental and structural requirements.