Most modern construction involves concrete. As technology and construction have evolved, so too has the use of this essential building material. Many techniques have been used to improve the application of concrete since it was first invented. One of the most recent innovations is sprayed concrete. While early forms of sprayed concrete used small cement guns, today’s sprayed concrete systems are extremely precise and powerful.
What is Sprayed Concrete?
Sprayed concrete is a method of concrete application where the building material is sprayed using a hose-like spray nozzle instead of being poured in the traditional manner. It can be applied to a variety of surfaces such as roofs, foundations, floors, walls, columns, and more. When applied properly, sprayed concrete is a durable and strong building material that does not need to rely entirely on metal reinforcement to maintain its structural integrity.
What are the Benefits of Sprayed Concrete?
Compared to conventional poured concrete, sprayed concrete has a lower water-cement ratio which allows for higher compressive strength. It adheres to surfaces and substrates better than regular poured concrete due to its high-pressure application. It can be combined with steel fiber reinforcement, allowing for more flexural strength and making the finished structure much more solid and sound.
Furthermore, sprayed concrete can be applied in large volumes at high speed, allowing for the creation of thick concrete structures. The concrete is applied, placed, and compacted in one process, reducing labor and speeding up construction times. Because of the lack of wastage inherent in this application process, the cost of sprayed concrete is also significantly lower compared to conventional concrete.
Thanks to its versatility, sprayed concrete is utilized in a variety of construction projects. It can also be used to repair damaged sections of existing structures. Some common uses of sprayed concrete include lining the inside of tunnels and mines, building curved structures like skate parks or swimming pools, and creating faux finishes and high-rise facades. In addition, since it is lighter than conventional concrete, it is suitable for use in the construction of taller and larger structures.
Wet vs. Dry Sprayed Concrete
There are two main methods used to apply sprayed concrete. The wet process is known as shotcrete while the dry process is known as gunite.
The Wet Process
In shotcrete concrete, cement, aggregates, and a prescribed amount of water and mixed thoroughly before entering the pump. This dense mixture is pumped through a hose to the spraying equipment where it is pressurized and shot onto the surface being repaired or built. Due to the high pressure that is used in this process, the shotcrete can compact tightly to the substrate without any air pockets.
The one major advantage of using shotcrete is that there is less dust generated in the wet mixture, resulting in a healthier environment for workers. Because of its density and compactness, shotcrete also boasts an extremely low permeability which makes it resistant to numerous environmental factors such as frost, freeze-thaw cycles, fire, mold, and subterranean burrowers.
The Dry Process
In gunite concrete, the ingredients such as sand, cement, and aggregate are dry mixed before being loaded into the spray system. The dry mix is fed through the hose with a high-velocity airstream. Along the way, it passes the water injection nozzle where it is combined with water to form a wet mix. The amount of water fed into the hose is determined by the worker operating the spraying nozzle.
Gunite provides greater control over the finish quality because the worker can control the levels of wetness and texture throughout the application. The holding time of the dry mix is almost unlimited before the addition of water, and it is quicker and easier to prepare than shotcrete mix. However, the success of the application depends heavily on the experience and capability of the hose operator.
Application Considerations for Sprayed Concrete
For optimum results, sprayed concrete has to be applied by trained operators. Sprayed concrete usually requires more experience and expertise than conventional concrete because the operator has to finely manage the water content of the applied concrete as well as the degree of compaction to achieve the desired strength, quality, and finish. Poor control of the application can lead to issues such as unsatisfactory adhesion to the substrate, cracking, sagging, shrinkage, and rippling.
When designing concrete joints and/or steel reinforcements, sprayed concrete is similar to regular poured concrete. It is important to consider the thickness, density, and characteristics of the resulting concrete to ensure its structural performance and durability. Similarly, sprayed concrete should be protected from the water before it sets and be allowed to cure properly for a week or so before any surface finishing to ensure an ideal result.
Modern construction relies on the use of different materials and equipment to improve the efficiency and quality of the end products. One of its main advantages of sprayed concrete is speed, which enables workers to quickly create high-quality concrete structures. Sprayed concrete also is more cost-effective than conventional concrete because it requires less labor and can be applied on almost any surface in any type of weather condition. If you are interested in using sprayed concrete in your next construction project, be sure to contact a reputable sprayed concrete contractor to find out if it is right for your needs.
