In recent years the importance of renewing and sealing entire sewer networks to prevent leaks and infiltration has been widely recognised by many sewer asset owners. This has created the need for experienced pipeline renewal contractors to be able to provide a range of solutions for complete sewer network renewal. As a consequence, the trenchless sewer rehabilitation market has evolved to the stage where treatment and renewal of access chambers have become important considerations in sewer rehabilitation works.
In sewer pipe rehabilitation it is an accepted practice to rehabilitate deteriorated sewer pipes before they fail in service. This approach allows for cost-effective and non-disruptive renewal. It is beneficial to apply this same maintenance approach to all sewer structures, including access chambers.
Renewing access chambers
Many of the reasons for rehabilitating access chambers are the same as those for rehabilitating sewer pipes; namely to repair and renew the structure, protect against gas attack, stop leaks and seal against infiltration.
Access chambers represent a significant proportion of the sewer network, accounting for approximately 30 per cent of the total surface area of the sewer. Therefore, leaving the access chambers untreated leaves a large section of the sewer network exposed to deterioration. Deterioration of access chambers caused by sewer gases is particularly common and in sewers where only the pipes have been lined, the problem is further exacerbated. This is because lining the pipes creates a gas sink in the untreated access chambers. The gases that naturally occur in the sewer can no longer affect the lined pipes and instead concentrate in the access chambers, thereby accelerating the rate of deterioration of the exposed access chamber surfaces. As such, it is important to prescribe a cost effective access chamber maintenance and renewal strategy as part of a total sewer renewal program.
As with most things that are in need of repair, an early fix to prevent further damage and thereby avoid more expensive repair costs later is important. This is also the case for access chambers because the extent and cost of repairs required will generally depend on the condition of the structure.
These figures show that the more deteriorated the access chamber is the higher the expected cost of repairs will be. The most economical course of action is to treat the access chamber early before any further deterioration leads to structural loss.
If an access chamber shows signs of deterioration but there is no structural loss then a suitable solution can include treating the exposed surfaces of the access chamber with a protective coating. The coating should seal the access chamber preventing leaks and infiltration and protect the access chamber from further gas attack and deterioration. A good quality coating applied by a specialist renewal contractor should effectively extend the life of the access chamber.
An important feature of protective coatings is a long service life in the level of protection provided by the coating. Accordingly, when selecting a protective coating for sewer applications the coating should be:
- non-sacrificial – e.g. made of resins or plastics
- strongly bonded to the substrate
- resistant to chemicals, especially those commonly occurring in sewer environments such as hydrogen sulphide
- resistant to corrosion
- resistant to abrasion
- resistant to impact and cracking.
In response to the demands of the industry, Interflow has recently developed a range of access chamber renewal products, Interchem, to enable cost-effective in-situ access chamber renewal. The Interchem product suite consists of a range of access chamber treatment products suitable for the condition of the access chamber.
P for Protect
Interchem P has been specifically developed for cost-effective treatment and protection of access chambers that show signs of gas attack but are not deteriorated to the point of structural loss. Interchem P is a non-sacrificial, multi-layer protective coating that is applied to the exposed access chamber surfaces. The coating consists of an epoxy primer base and a polyurea top coat. The finished product is a water-tight, chemically resistant, hard-wearing coating that is flexible enough to handle normal ground movement and surface traffic vibrations without cracking.
The first step Interchem P protective treatment process is to inspect the condition of the access chamber to determine if application of the protective coating is appropriate. If the access chamber is not severely deteriorated and there is sufficient structure left, Interchem can be considered suitable. Otherwise, a thicker and stronger rebuild treatment, such as Interchem R, may be required. All exposed surfaces are then thoroughly cleaned with high pressure water to remove surface contaminants. If there are any surface cracks and leaks present, these are filled and sealed prior to applying the coating. Tests are carried out to confirm that cleaning and pre-treatment work have been carried out correctly. The cleaned access chamber surfaces are coated with a high performance epoxy primer, which ensures strong adhesion of the coating to the substrate. After the primer has cured, the polyurea top coat spray is applied and cures in seconds, creating the finished product.
A key benefit of using polyurea as an access chamber coating is that it has material properties ideally suited for application in sewer environments. Polyurea has excellent resistance to chemicals, particularly to commonly occurring sewer gases such as hydrogen sulphide. Polyurea also has excellent resistance to abrasion, impact and cracking. These properties mean that Interchem P can often be applied in a thinner layer than similar cementitious or epoxy based coatings and can provide a high level of protection.
The advantages of utilising polyurea spray technology include its fast application and rapid resin cure. A typical polyurea coating thickness of 3 mm can be sprayed and will cure in a matter of seconds. This translates to faster application rates, so there is less disruption to local residents and traffic during installation.
Interchem P is a cost-effective method of treating gas attacked access chambers that are not yet structurally deteriorated. The coating can seal, protect, renew and extend the life of the access chamber. For access chambers that are highly deteriorated and require some structural restoration, Interchem R is an ideal treatment product.
Conclusion
Access chambers represent a significant proportion of the sewer network and so should be an important consideration in any sewer rehabilitation works program. When faced with the situation of renewing access chambers, it is important to address the problem as early as possible so that a cost-effective treatment can be provided before the deterioration spreads and a more disruptive and expensive repair cost is likely. Protective coatings, such as Interchem P, offer an excellent solution for sealing, protecting and renewing access chamber before any structural loss has occurred. For access chambers that have some structural loss, a thicker rebuild coating such as Interchem R may be required. A specialist sewer renewal contractor can provide assistance and recommend the optimum solution according to the manhole condition. This will ensure the asset owner gets the best value for money in asset maintenance.