A Complete Guide to Shotcrete Sprayers and Applications

An Introduction to Shotcrete Sprayers

Shotcrete, also known as sprayed concrete, is a popular method of applying concrete to various surfaces and structures. Unlike traditional poured concrete, shotcrete is sprayed onto a surface at high velocity through a hose and nozzle. This allows it to adhere tightly even on vertical or overhead surfaces. Shotcrete has many advantages over poured concrete such as speed of application, less formwork required, and versatility on complex shapes and surfaces. One of the key pieces of equipment used for shotcrete application is the shotcrete sprayer.

What is a Shotcrete Sprayer?

A shotcrete sprayer, sometimes referred to as a concrete pump or shotcrete machine, is a piece of equipment that mixes and sprays shotcrete onto a surface. It consists of a concrete pump that pushes premixed concrete through a hose where it is then sprayed out of a nozzle at high velocity. The shotcrete is propelled by compressed air supplied by an air compressor. The nozzleman controls the direction and amount of shotcrete applied.

There are two main types of shotcrete sprayers:

• Dry-mix shotcrete sprayers - Dry ingredients of sand, cement and aggregates are mixed on site then loaded into the machine's hopper. Water is then added at the nozzle as the shotcrete is sprayed.
• Wet-mix shotcrete sprayers - Concrete is batch mixed off site with water then loaded into the pump's hopper ready to spray. No mixing required on site.

How Do Shotcrete Sprayers Work?

The shotcrete spraying process works as follows:

1. Premixed concrete is loaded into the hopper of the shotcrete pump.
2. The concrete is pushed by pistons or a rotor through the hoses towards the nozzle.
3. Compressed air from the air compressor is injected at the nozzle.
4. The concrete and air mixture is propelled at high velocity through the nozzle onto the receiving surface.
5. The nozzleman controls the direction and amount of shotcrete sprayed.
6. The concrete adheres tightly to the surface even on vertical or inverted sections.

The addition of compressed air at the nozzle allows the concrete to be sprayed accurately onto the surface at high velocity. The accelerated concrete impacts and sticks tightly even on overhead or vertical applications.

Types of Shotcrete Sprayers

There are a few different types of shotcrete sprayers available:

Trailer Pump Shotcrete Sprayers

These are portable shotcrete pumps mounted on a trailer frame. The trailer can be towed to different locations by a truck. Trailer pumps have capacities around 6 to 8 cubic yards of concrete per hour. They are suitable for small to medium shotcrete jobs.

Truck Mounted Shotcrete Sprayers

These shotcrete pumps are mounted on heavy duty truck chassis. They have larger concrete capacities in the range of 30 to 150 cubic yards per hour. The highly mobile setup allows efficiency on large jobsites. Truck pumps are operated by a driver and nozzle operator.

Robot Shotcrete Sprayers

Robot shotcrete sprayers feature an arm or robotic nozzle that is remotely controlled. They provide improved precision and reduce overspray compared to manual nozzle operation. Robots allow shotcrete application in hazardous areas without risk to workers. They are growing in popularity for tunneling, mining and repair projects.

Benefits of Using Shotcrete Sprayers

Some of the benefits of using shotcrete sprayers over traditional concrete placement include:

• Faster application of concrete.
• Require less large-scale formwork.
• Can adhere to complex shapes and vertical/overhead sections.
• Lower rebound waste compared to pumped concrete.
• Provide a tight consolidated concrete layer.
• Can be applied in hard to reach areas.
• Allow early strength development.
• Require less labor to implement.

The speed, efficiency and versatility of shotcrete makes it an ideal solution for many concrete construction projects. Proper use of a quality shotcrete sprayer allows you to maximize these benefits.

Shotcrete Sprayer Maintenance

Like any construction equipment, shotcrete sprayers require regular inspection and maintenance to ensure optimum performance. Some key maintenance tasks include:

• Inspecting pumps, valves and hoses for wear or damage.
• Lubricating seals, bearings and moving parts.
• Checking safety devices and nozzles are functioning.
• Cleaning buildup of residual concrete from inside pump and hoses.
• Replacing any damaged hoses or nozzles.
• Checking compressor air filter for cleaning or replacement.
• Greasing and oilingmoving parts as required.

A well maintained shotcrete sprayer will have optimal pumping performance and reduced likelihood of breakdowns. Always consult the equipment's maintenance manual for the manufacturer recommended schedule and procedures.

Safety Tips for Shotcrete Sprayers

There are some important safety considerations when working with shotcrete sprayers:

• Wear proper PPE - hard hat, respirator, eye protection, ear plugs and protective clothing to minimize exposure.
• Establish a safe perimeter to keep unprotected workers away from dust and rebound splatter.
• Use caution around pressurized hoses and don't attempt repair while equipment is operating.
• Ensure adequate ventilation when working in enclosed areas.
• Follow manufacturer operating instructions and safety guidelines.
• Check equipment condition and safety devices prior to each use.
• Only allow properly trained operators to use the equipment.

With proper operating procedures and training, shotcrete sprayers can improve project efficiency while maintaining a safe working environment.

The Versatility of Shotcrete Sprayers

Shotcrete sprayers are extremely versatile concrete placement tools. When operated by a skilled nozzleman, they can be used to apply high quality concrete in almost any situation. Here are some examples of the versatility of shotcrete sprayers on different applications:

Pool Construction

Shotcrete allows fast, efficient application of concrete over contoured pool surfaces. It can be applied vertically to form pool walls and reduces the need for large forming structures.

Tunnel Linings

Sprayed concrete is extensively used to create durable tunnel linings. Robot shotcrete sprayers improve safety in this hazardous environment.

Slope Stabilization

Shotcrete can be sprayed onto slopes and retaining walls to prevent erosion and landslide risks. Anchor bolts can also be installed during application.

Repair Work

Damaged concrete structures like bridges, parking garages and balconies can be repaired quickly with shotcrete. It provides excellent adhesion to existing surfaces.

Thin Repairs

Thin layers of shotcrete allow resurfacing and repair of deteriorated slabs while minimizing changes to structure height.

Fireproofing

Applied as a thin coating, shotcrete provides excellent fire protection to steel beams and columns in buildings.

Artistic Structures

Shotcrete's ability to form free-flowing shapes allows creation of decorative rockscapes, artificial rock climbing walls and artistic sculptures.

These examples demonstrate shotcrete's adaptability to meet a wide range of construction challenges. Maintaining a well-functioning shotcrete sprayer expands the possibilities of what you can build.

Tips for Effective Shotcrete Application

Achieving high quality shotcrete application relies heavily on the skills of the nozzleman and ground crew. Here are some tips for effective shotcrete spraying:

Prepare the Surface

The substrate needs to be clean, free of loose material and suitably prepped. Apply a bonding agent if required. Thorough surface preparation results in better shotcrete adhesion.

Adjust Nozzle Angle

The nozzle should be oriented at right angles to the surface during application. This maximizes velocity and reduces rebound splatter.

Use Proper Distance

Maintain the correct distance from surface based on the shotcrete pump's capacity. This avoids excess buildup and sagging.

Apply Uniform Layers

Overlap spray patterns to ensure uniform depth across the entire area. This prevents weak spots.

Limit Rebound

Excessive rebound concrete is wasteful and requires cleanup. Proper technique minimizes overspray and rebound.

Monitor Slump

Check concrete consistency in the pump hopper. Adjust slump if the mix is too wet or dry for proper application.

Control Joints

Install control joints to the sprayed surface to prevent later cracking from shrinkage and stresses.

Watch Wind Speed

Wind can make shotcrete application difficult and cause rebound issues. Monitor conditions and avoid spraying in high winds.

Learning proper techniques, having an experienced crew and monitoring all aspects of the shotcrete process will achieve superior results.

FAQs

What is the difference between shotcrete and conventional concrete?

The main difference is shotcrete is sprayed at high velocity onto a surface, while conventional concrete is poured into forms. Shotcrete can adhere to vertical and overhead surfaces without forms.

What advantages does shotcrete provide over poured concrete?

Shotcrete is faster to apply, requires less formwork, can be used on complex shapes, has lower rebound waste, allows early strength gain and requires less labor.

What kind of compressor is required for a shotcrete sprayer?

Shotcrete sprayers require a high volume, large CFM air compressor to provide adequate air for high velocity spraying. Compressors of 175 CFM or greater are normally used.

What maintenance should be performed on shotcrete equipment?

Routine maintenance like cleaning buildup, lubricating parts, inspecting pumps and hoses, checking safety devices and replacing worn parts as needed.

What safety precautions should shotcrete workers take?

Proper PPE, establishing safe perimeter, adequate ventilation, following manufacturer guidelines, properly trained operators, and care around pressurized equipment.