Instead of pouring traditional concrete into moulded form, shotcrete uses a hose to pneumatically spray concrete onto a receiving surface. This advanced technology is ideal for swimming pools, skate parks, tunnels, drainage, slope stabilisation, and other civil engineering challenges. There are many advantages that shotcrete offers over traditional concrete, such as decreased labour and materials along with increased efficiency and productivity.
Despite the advanced technology, one of the biggest challenges that shotcrete contractors face is insufficient consolidation by inexperienced nozzleman. Since shotcrete has the potential to be more permeable and have bigger and more frequent voids, experienced nozzleman are required given that they have the skills and ability to spray shotcrete with enough velocity to allow it to be consolidated. Proper consolidation is vital to ensure the structure is free of any imperfections such as voids, cracks, and joints. These imperfections result in waterproofing problems as the results are comparable to vibrating cast-in-place concrete but with less risk of segregation.
Waterproofing shotcrete can be difficult even for contractors who are experienced with cast-in-place concrete. So, how do contractors waterproof shotcrete structures? Are these methods reliable? Let’s look at some of the methods that are used to waterproof shotcrete today and in the past.
Surface-applied waterproofing systems
There are two primary types of surface-applied waterproofing systems which are surface coatings and sheet membranes. Both these systems have been used extensively in the past and are either polymer or bitumen based.
- Surface coatings
Surface coatings have been widely used in the past considering that they work with projects involving multiple plane transitions, complex geometrical shapes, and protrusions. Despite this, the surface coatings tend to deteriorate when exposed to the sun or when the surface experiences heavy foot traffic.
- Sheet membranes
Sheet membranes are essentially flexible sheets that are fixed to the wall and sealed at the seams. While this method has superior crack-bridging ability, it suffers from the same limitations as surface coatings.
The problem with both these methods is that preparing the surface by installing either a coating or membrane is very time-consuming and costly. Furthermore, the surface barrier is likely to be damaged when spraying shotcrete at a velocity of approximately 100 psi onto the receiving surface, and once the coating or membrane has been damaged, it’s essentially useless. Other studies have found that the chemicals used in both coatings and membranes do not adhere to most project’s environmental requirements in modern times.
Integral systems involve admixtures that are added to pre-mix concrete at the batching plant. Rather than forming a barrier on the surface of the concrete, the admixtures produces a concrete that is a water barrier in itself. In contrast to surface-applied waterproofing systems, no costly surface preparation is needed, no additional labour or materials are needed, and the system cannot be punctured or scratched.
- Reactive/crystalline systems
When the crystalline system is added to the concrete mix, the chemicals grow millions of microscopic needle-like crystals which block the movement of water. Once the concrete has been set, these crystals become inactive until cracks appear, at which point they react with the incoming water and virtually self-seal the crack and maintain a watertight barrier. The disadvantage with this system, however, is that cracks and joints can take time to self-heal.
- Waterproofing solution
The current best practice of waterproofing shotcrete is using crystalline waterproofing solution. Being an integral system, crystalline waterproofing is not vulnerable to damage or poor workmanship and has the ability to withstand extreme hydrostatic pressure. Additionally, this system has a compatible waterstop that can withstand the violent shotcrete application process. The crystalline waterproofing system has additional sustainability benefits, which further increases the attractiveness of this method in today’s times.
The evolution of waterproofing shotcrete has been relatively fast, considering that shotcrete has been used in the construction industry for over 50 years. Today, the crystalline waterproofing solution is by far the best method of waterproofing shotcrete because it doesn’t involve expensive surface preparation and isn’t prone to damage or unskilled workmanship.
If anything, this highlights the importance of using experienced shotcrete contractors who are qualified and trained in the application of shotcrete. If you have any further questions relating to waterproofing shotcrete, reach out to the professionals at Evolution Shotcrete by phoning 07 5561 8885.