As the trenchless industry continues to develop and grow, so too does the technology for in situ underground pipeline rehabilitation. Today there is a wide range of products for in situ repair and rehabilitation of sewer pipelines and systems. For the asset owner, the selection and specification of the appropriate product is becoming increasingly difficult as the product offerings become more diverse.

Before discussing the details of the resin types it is helpful to firstly define where resin-based systems fit, in terms of the types of products on offer.

In the broadest sense, materials used for pipeline rehabilitation will either be considered sacrificial (repairs) or ‘permanent’ (renewed). The line between these types of products can be a little grey in some cases, but broadly a permanent solution would be expected to have a service life similar to that of a component of a new pipeline. A sacrificial product will tend to gradually wear away and either need re-doing in the near future or ultimately, be replaced by a more permanent product. Resins in Australasia

In the Australasian market, the majority of rehabilitation expenditure is on permanent or long term solutions; as such; the majority of the products tend to be thermoplastic or thermosetting resin based. There is, nevertheless, a market for the use of sacrificial materials, the most commonly used being cement based products. The main benefit of cement based products is that they often have a lower upfront cost; however they are rarely the best value for money when the total life cycle cost is considered, hence the lower rate of usage in this market.

The products used for long term renewals will tend to be either pre-fabricated or ‘wet’ applied – resin based systems being the latter. Before discussing resins, it is useful to discuss the use of the pre-fabricated products.

Pre-fabricated products

Pre-fabricated products are those that are primarily manufactured offsite and delivered to site ready for installation. The installation process will typically be a mechanical process rather than a chemical process. Examples of pre-fabricated products include spirally wound PVC liners, such as Interflow’s Expanda®, fold and form liners, slip lined products and pipe bursting products. In the case of Expanda the product is delivered to site in strip form and mechanically wound to the form of a PVC pipe in situ.

An advantage of the pre-fabricated products is that they are already in their final chemical state when delivered to site, i.e. they are not created onsite. As such the final properties are not affected by site conditions, installation practices, ambient conditions, or pipe conditions. The use of pre-fabricated products for lining sewer pipes in Australia far outweighs the use of resin based systems. It is estimated that greater than 75 per cent of all sewer lining is performed with pre-fabricated lining systems.

The use of pre-fabricated products in the trenchless pipeline renewal industry is consistent with the general trends in other industries. The building industry for example has seen a decreased usage of ‘wet’ processes such as plastering, rendering and concreting in exchange for using pre-fabricated panels and pre-cast structures. Driving the trend is the desire for cleaner and safer work sites, improved productivity, better quality control, and lower cost.

Notwithstanding the use of pre-fabricated systems, there are many areas of trenchless pipeline renewal that require, and are best served by, the use of resin based systems. The following sections cover some of the types of resins that are used and the reasons why they are used.

The role of resins in trenchless renewal Certain site conditions, locations, pipe geometries, or applications make resin based systems ideal. Examples of this include spot repairs, sealing systems, lateral connection repair, surface protection coatings, and access chamber renewal.

Because they are initially in a ‘soft’ or ‘wet’ state, resin based liners can be formed to allow application to awkward shapes and tight locations. This is the principle behind cured-in-place pipe (CIPP) liners and is a reason why resin based systems are commonly and effectively used for patching of pipes, lateral connection repair, lateral lining and indeed whole pipelines.

Resins are also suited for surface protective coating applications because they generally exhibit good long term chemical resistance, good abrasion resistance and high adhesion strength. Resins can also be blended with aggregates to create a strong hard-wearing material that can be applied in thick layers for structural rebuild of deteriorated sewer surfaces.

The right resin for the job

There are many different resin types that serve many different applications. The following section covers the properties, features, limitations, and applications of some of the more commonly used resin types. Polyester

A polyester resin contains the base resin and thermally activated initiators. The initiators are peroxide based chemicals and are added in small quantities. When the resin system is heated, the initiators decompose and release free radicals, which in turn cause the polyester resin to polymerise (cure). The nature of this, and most free radical initiated polymerisations, is that the product will shrink during cure.

Polyester exhibits good durability and good resistance to chemicals and water. The major advantage of polyester resin is that it is relatively low cost, which is why it is commonly used for CIPP lining applications in the trenchless sewer industry, where the volume of resin required is very high. In CIPP liners, the polyester resin is typically impregnated into either felt or glass fibre matting. In order to initiate the cure, either steam or heated water will be circulated through the liner or an ultraviolet light train will be pulled through the liner.

Polyester resins have proven to be a very suitable material for pipeline renewal over many years. Experienced users of the system have learned to compensate for shrinkage and control the cure such that the polymerisation occurs in the desired manner.

The most serious drawback of polyester resins is the presence and need to control styrene (aka vinyl benzene). Styrene is present in virtually all polyester resins. Like many derivatives of benzene styrene is noted as a “Potential Human Carcinogen” by the International Agency for Research on Cancer and as a “Suspected Carcinogen” by the Environmental Protection Agency and it is generally advised to treat the chemical as a hazardous product. Styrene has also been shown to be toxic to aquatic organisms, so it is essential that styrene does not enter the waterways or sewerage systems.

When handling polyester resins it is essential that appropriate control methods, disposal practices and monitoring are put in place to eliminate the risks to workers and residents. Epoxies

Epoxy is formed from the reaction of an epoxide ‘resin’ with a ‘hardener’. The resulting polymer is strong and hard. Epoxy can cure underwater and exhibits strong adhesion, good chemical and abrasion resistance, and high strength.

Epoxy resins are free of styrene and exhibit minimal shrinkage. Epoxies are, in many ways an ideal material for a broad range of applications.

The two main issues that restrict the use in the trenchless pipeline renewal industry are the cost and speed of cure. From a cost perspective, it is several times more expensive per kilogram than polyester resins. As such, it becomes too expensive to be competitive for high volume applications as a viable CIPP resin. Secondly, the chemistry of an epoxy reaction does not give the same degree of flexibility and control as a free radical initiated system. As such, it is more difficult to have both a long working time at ambient temperatures and a short fast curing time.

Epoxies have proven to be excellent materials for applications such a patching, sealing, lateral lining and protective coating. In each of these applications the high strength, broad chemical resistance and strong adhesion characteristics make epoxy an ideal choice.

Epoxy can also be mixed with fillers typically used in cement based mixtures to create an epoxy mortar. The epoxy mortar combines the chemical resistance and hard wearing properties of epoxy with the high compressive strength and low cost of the filler material. The resulting product can be used for cost-effective structural rebuilding of deteriorated sewer surfaces. In recent years, epoxy mortars have been widely used in NSW for renewing large pipelines and access chambers. These materials can be applied either by hand or sprayed. An example of an epoxy mortar product is Interflow’s Interchem™ R for structural repair of deteriorated sewer structures.

Polyurea

In more recent years polyureas have started to be used in the trenchless pipeline renewal market. Polyurea is formed from the reaction of Isocyanate with Polyol. The result is a rapid setting product that is hard wearing, has high impact strength, high resistance to cracking, and excellent resistance to chemicals.

Polyurea has a low flexural modulus, so it is not suitable for structural applications and it also requires application of a primer to provide strong adhesion to the substrate surface.

Polyureas are excellent as protective coating materials. They are extensively used as floor coatings and for protection of steel and concrete structures in a wide variety of industries. The key properties that make them so widely accepted are the ease and speed of application, and the long term durability of the finished product against chemicals, impact and abrasion.

In the trenchless industry, polyureas are ideal for applying a protective coating to cement based structures before the extent of deterioration has caused excessive structural loss, i.e. as a preventative measure. In particular, polyureas are ideal for manhole, pump stations, treatment plants and other associated structures. Polyureas are spray applied and because they cure in a matter of seconds, they are ideal as surface protection coating on vertical and overhead surfaces. An example of a polyurea is Interflow’s Interchem™ P, which has been used in the Australian market for two years for access chamber renewal. Silicate resins

Silicate resins fill the gap between the fast curing, but flexible, polyurea products and the slower curing but strong epoxy resins. The chemistry of silicate resin is similar to that of polyurea. However, the presence of a silica based interpenetrating network leads to a product with substantially higher flexural modulus. As such, silicate resins are ideal for applications where a fast cure is required at ambient temperature and the product needs to have a reasonable amount of strength.

Silicate resins are typically mixed by hand at room temperature rather than being sprayed, although it is possible to spray them as well.

Silicate resins have good adhesion properties and when cured have good abrasion and chemical resistance. Another feature of silicate resins is that they do not shrink. In fact, they can expand slightly during cure. This property helps with adhesion and makes silicate resins ideal for sealing applications where penetration into a crack or small cavity is desirable. In recent years, silicate resins have been employed in patching applications and in lateral connection sealing. An example of this is Interflow’s award winning Interfit™ product for lateral connection sealing. The use of the silicate resin for this application was a first for the industry in Australasia and it has now become the norm.

Silicate resins are non-toxic and safe for workers and residents. From an environmental perspective, silicate resins contain a low proportion of fossil fuel-based constituents, and as such are an environmentally responsible material choice. Summary

In summary, resin technology has played, and will continue to play an important role in providing effective trenchless solutions to pipeline rehabilitation. Resin based systems have life cycle cost advantages over traditional cement based products making them an attractive choice for coating and sealing applications. Resin based systems are ideal for applications where installation of pre-fabricated systems is not possible.

However, choosing the right resin for the job is not necessarily a simple task given the vast array of resin types on offer. Selecting the optimum solution will depend on the application, cost, quality, and consideration of safety, community and environmental factors. A specialist sewer renewal contractor with a complete range of pipeline repair products, such as Interflow, can provide assistance and recommend the appropriate product for the application.