Shotcrete concrete: properties, preparation and methods of application

Shotcrete is a common form of concrete application used in construction and repair projects because it is effective and versatile. It is applying a thick, long-lasting layer to a surface by rapidly spraying a concrete mixture onto it. This technique has a number of benefits, such as quick application, superior adhesion, and the capacity to cover intricate shapes and difficult-to-reach places.

Shotcrete’s characteristics make it perfect for a range of uses. Its exceptional strength and resilience guarantee long-lasting functionality, and its versatility makes it suitable for use in retaining walls, swimming pools, tunnels, and even sculptures. Shotcrete can be applied either wet or dry, with particular preparation and application methods for each method.

To create shotcrete with the appropriate strength and consistency, careful material selection and mixing are required. Cement, sand, aggregates, water, and performance-enhancing additives are usually included in the mixture. Since the mix’s quality directly influences the concrete’s final properties, it is essential to the application of shotcrete.

Shotcrete is applied primarily using two methods: the wet-mix method and the dry-mix method. All of the ingredients are combined with water and then pushed through a hose to the nozzle, where compressed air forces them to the surface, in the wet-mix method. The hose is used to feed the dry ingredients into the dry-mix process, where they are combined with water at the nozzle. Every approach has benefits of its own and is selected according to the particular needs of the project.

Shotcrete is an important tool in contemporary construction because of its efficiency and versatility. Shotcrete offers a dependable and efficient solution for a variety of tasks, including surface repair, decorative construction, and tunnel reinforcement. It is a great option for many applications due to its rapid and waste-free formation of strong, durable layers.

Properties	Preparation and Methods of Application
High strength and durability	Mix cement, sand, and water to form shotcrete; use a nozzle to spray onto surfaces
Excellent adhesion to surfaces	Can be applied using dry or wet-mix methods
Resistant to fire and weathering	Requires specialized equipment for application
Good for complex shapes and structures	Commonly used for tunnels, retaining walls, and pools
Fast application and setting time	Proper curing is essential for best results

A versatile material with exceptional bonding strength and durability, shotcrete concrete is perfect for a range of construction projects, such as tunnels, swimming pools, and repair work. This article examines the special qualities that make shotcrete stand out, goes into how to prepare for best results, and talks about the different ways to use it that make it a popular option in contemporary building.

Composition and main characteristics of shotcrete concrete

The components used to produce the concrete mixtures used to make shotcrete must be chosen with consideration for the operating and technical conditions of the structures as well as the design documentation for each unique situation.

Materials for the preparation of shotcrete concrete

According to the existing technical specifications, the raw materials for making concrete mixtures must be kept in closed dry rooms.

Standard shotcrete solutions are made with the following ingredients:

Binders

This kind of concrete is prepared using the binders that come in the following varieties:

• slag Portland cement, Portland cement (GOST 10178);
• sulphate-resistant cement corresponding to GOST 22266;
• white Portland cement for decorative coatings (GOST 15825).

Fillers

The following substances can be used as fillers when shotcrete is used to prepare concrete:

• quartz sand;
• gravel or crushed stone of small fractions;
• lightweight fillers (GOST 9757).

The equipment’s capacity and the specifications for the concrete coating’s thickness determine the filler’s maximum grain size. For instance, aggregates with a maximum particle size of 10 mm may be used for concrete surfaces up to 50 mm thick.

Additionally, the following specifications must be fulfilled by materials used as aggregates:

• relative humidity 2–7%:
• clay particles in the aggregate should be no more than 0.5%;
• the composition of particles with a fraction of less than 0.14 mm should not exceed 10%;
• the maximum content of coarse aggregate grains (>5 mm) is 5% or less;
• all materials used as aggregates must have a smooth and rounded shape.

Note: Using crushed materials with sharp edges is not advised as this can cause premature equipment wear and worker injuries in the event that the material bounces off the concrete surface.

Modifying additives

The mixture can be supplemented with the following chemical and mineral ligatures to obtain the necessary properties for shotcrete concrete:

• microsilica;
• fuel ash;
• calmaflex (water-repellent additive);
• plasticizers;
• stabilizers, accelerators or retarders of hardening, etc.;
• pigments for decorative coating.

Requirements for shotcrete mixtures

The design documentation, which outlines the essential technological characteristics that the newly laid and hardened coating should have, is followed when choosing the composition of the concrete mortar, including the quantity of water, fillers, binders, and necessary modifying additives.

Conditions necessary for mixtures of shotcrete concrete:

1. The minimum volume of cement in the mortar is 300 kg/m3.
2. The maximum volume of mineral additives is reflected in the table (see. photo).

1. Tensile-compressive strength corresponds to the brands of shotcrete concrete: B25–B60.
2. Each class of concrete corresponds to a recommended grade of cement (table).

1. The water resistance of Concrete Thorn is W4 – W
2. Frost resistance is characterized by brands F50 – F
3. The water -cement ratio, depending on the humidity of the aggregates, is taken within 0.4-0.5.
4. When calculating the required volume of water, it is necessary to take into account the optimal rigidity of the concrete mixture (recommended 20-60 s).

Calculation of the composition of concrete

Methods of fragmentation

By using concrete to construct the Torkret, you can completely automate the production of concrete work, minimize the amount of installed formwork, and in certain situations, forgo it entirely.

Shotcrete is frequently used in new construction, the reconstruction of dilapidated buildings that have been destroyed, and the application of protective coatings that lengthen the lifespan of concrete structures:

• construction of structures for water supply (water towers, tanks, etc.);
• construction of hydraulic structures;
• finishing of underground structures;
• fastening of the edge of construction pits;
• reconstruction of road and railway tunnels;
• installation of special coatings in the construction of industrial buildings;
• restoration and strengthening of concrete structures;
• installation of counter-supports under existing building foundations;
• installation of special wear-resistant and chemically resistant protective coatings.

Two kinds of shotcrete mixtures exist, based on the filler’s grain size. Compositions with a filler size of up to 10 mm fall into the first class, while spray concrete has a filler fraction of up to 25 mm in the second. The benefit of using spray concrete mixture is that concrete work can be done without the need for formwork.

Spraying is done directly onto the walls, ceilings, columns, and other structures that need to be repaired. Shotcrete can be applied using one-sided formwork in new construction.

There are two ways to apply concrete: dry and wet. This is because shotcrete work requires specific technological requirements and conditions. An example of shotcrete application on a wall is shown in the video.

Dry shotcrete

All of the dry materials needed for the task are combined and pre-dosed. After that, they are fed into the shotcrete unit’s receiving hopper, where they are fed into the nozzle (sprayer) at a high air pressure. The dry mixture is mixed with water at the sprayer’s base, and then it is sprayed onto the surface of the base that is being built or repaired using air pressure.

The water pressure and the unit’s internal air pressure, which is produced by a compressor, must remain constant when drying shotcrete.

The equipment that is required includes:

• shotcrete unit;
• water tank;
• compressor;
• high-pressure hoses;
• nozzle.

• the process of pre-mixing the mixture with water is eliminated;
• The supply of the mixture of the mixture over significant distances:
• High performance with the possibility of applying thick coating in one pass:
• Simple cleaning of hoses and basic equipment.

Wet method of fragmentation

During the preparation stage, the dry concrete mixture is combined with water and, as a result of its own weight, falls into the screw compartment located on the installation floor. It is then delivered to the nozzle with the aid of a screw pump, where it is propelled to the ready surface by compressed air.

Benefits of using a wet method:

• A well -mixed homogeneous mass comes out of the sprayer;
• less rebound in comparison with the dry method;
• lack of dust, unlike dry spraying;
• The possibility of finishing surface processing.

• the impossibility of applying a concrete layer of more than 3 cm;
• increased shotcrete time due to slow distribution of the mixture along the base of the structure;
• labor-intensive operation of washing and cleaning equipment.

You can use ready-made concrete mix that has been prepared in the factory for the wet method of shotcrete, or you can make it on site yourself if you have the necessary equipment.

With so many uses, shotcrete concrete is a useful and efficient material. Because of its special qualities, like its great strength and longevity, it is perfect for intricate construction projects. Shotcrete is a dependable material for building new structures as well as repairing existing ones.

To get the right consistency and strength, shotcrete preparation requires precise mixing and careful material selection. A smooth application and good surface adhesion are guaranteed by careful preparation. Although specific equipment may be needed for the process, the end results are well worth the effort.

Shotcrete can be applied in a variety of ways, each according to the requirements of a particular project. Applying the material evenly and with the proper pressure is crucial, regardless of whether you choose to use the wet-mix or dry-mix method. This guarantees a solid bond and a seamless completion.

All things considered, shotcrete concrete has many advantages for a range of building projects. Builders and engineers can find it to be a useful alternative due to its strength, versatility, and simplicity of use. Through comprehension of its characteristics and appropriate methods of use, shotcrete can be utilized to its fullest potential.

Video on the topic

Use of shotcrete concrete, pneumatic concreting, where the method of spraying concrete is used

His Majesty dry shotcrete. We start on the mixture that we make ourselves.

Wet shotcrete. Making a leveling layer on the SVG of the tunnel.

Cleaning the walls with air 12 m3 / min. before spraying concrete. Shotcrete mixture Khimtek. Rivne region

Strengthening arches using the wet shotcrete method

Work for men. Confrontation with concrete.

The team does not care how expensive material is killed and technology is violated!

Wet shotcrete technology. Basics. Equipment. Part 2