Fibre reinforced polymers (FRPs) are increasingly being used in construction due to their light weight, ease of installation, low maintenance, tailor made properties, and corrosion resistance. The UK FRP industry produces 240,000 tonnes of products a year with 11% of this being for the construction industry. Current and impending waste management legislation will put more pressure on the industry to address the options available for dealing with FRP waste. Such waste legislation focuses on dealing with waste through the waste hierarchy and will therefore put more pressure on solving FRP waste management through recycling and reuse.

At present the most common disposal method for UK FRP waste is landfill. To assist in the transition from disposal in landfill to recycling, the FRP industry needs to consider designing materials and components for easier deconstruction, reuse and recycling at the end of the product life.

EU Directives

EU directives such as End of Life Vehicles (ELV) and Waste Electrical and Electronic Equipment (WEEE) will put more pressure on solving FRP waste management through recycling and reuse. The ELV directive states that by 2015, 85% of ELVs will have to be reused or recycled (excluding energy recovery), with only 10% incinerated with energy recovery, and only 5% going to landfill1. Whilst this new legislation does not impact on the construction industry, currently in negotiation is the proposed EU recommendation on Construction and Demolition Waste, which if adopted will have a significant effect. FRP suppliers could lose their market share to metal and other industries if they cannot ensure that their FRP components can be reused or recycled at the end of their life.

The Waste Hierarchy

According to the waste hierarchy, the options for FRP waste management in order of preference are waste minimisation, reuse, recycling, incineration with energy recovery / composting, and lastly incineration without energy recovery / landfill.

Most Desirable

Reduction

↓

Reuse

↓

Recovery

↓

Disposal

Least desirable

Figure 1: The waste hierarchy

Waste Minimisation

The most cost effective and environmentally beneficial option of waste management is not to produce the waste in the first place. By reviewing the manufacturing process it may be possible to identify a method which results in less production waste. Waste minimisation does not assist in complying with the ELV directive, but may be useful to consider in the face of increasing landfill charges and the development of corporate environmental policies. It could also identify where practicable cost savings can be made.

Waste takes a variety of forms such as off-cuts, overspray trimmings, trimming dust, trimming from vacuum infusion, defective items and trials runs, plus obsolete moulds. Most automated processes are very efficient and there is little scope for improvement in terms of reducing generated waste, although waste may be generated at the beginning and end of production runs, or if components fail to meet accepted standards e.g. through a faulty set up.

Most of the waste produced is disposed of by landfill. Some manufacturers bear the cost of sending bulky waste via skip container to landfill using a contractor, and there is considerable scope for reducing this burden. Contamination of FRP waste which could be recycled with other waste such as resin containers, release agent, rainwater, cleaning rags etc is an important issue.

Reuse

Reuse is high in the hierarchy, but it is debatable how practical this might be. An FRP component is composed of at least two constituents working together to produce material properties that are different from the properties of these elements on their own. The way in which FRPs are used, their applications and how they are secured to existing structures must be considered with a view to deconstruction and reuse at the end of that application's life. The manufacturing process must be examined to identify any possible modifications to improve design for future reuse or recycling. Avoiding embedded metal fixings which are difficult to separate prior to grinding is one example.

Many FRP items are bespoke in nature, being especially designed for a particular application or building (e.g. mouldings and facade panels), meaning that it is very unlikely such products will to be able to be reused for another, different application. Items such as FRP swimming pools, cess pits and pipes are designed with very long service lives and are not installed with recovery or reuse in mind. One possible option is a downgrading of product use e.g. tanks and silos for use in agriculture. However, there is potential to reuse FRP features such as domes, clock towers and chimneys. Indeed, reuse of items like cabins and gatehouses already takes place.

Structural items such as sections or I beams may be difficult to reuse since it is difficult to re-calculate their load carrying properties as recovered items, or reliably access any degradation or creep effect. This is quite different from the situation for recovered steel girders, large section timbers, and old bricks, for example, all of which are reclaimed and have a market value today. Without reference to the original manufacturer it will be difficult to derive the strength characteristics such as shear and bending of an FRP section with unknown matrix/fibre combination and makeup. FRP sections also tend to be produced to meet a particular set of circumstances and conditions so will often not be transferable to a different use. The designer of a building or structure will have a duty of care to make sure it is sound and a material cannot be reused if its strength properties are unknown or in doubt. This also applies to any fixings, bolt holes etc for FRP claddings and mouldings. Similarly, care must be taken with reuse of cladding or roofing to ensure its fire-resisting properties are known.
Development of modular and prefabricated systems should allow reuse if this aspect is considered at the design stage, especially in respect of the type of site applied sealing and gluing of joints.

Although FRP manufacturers have largely solved issues relating to UV stability and colour fading of their products, many fascia panels and mouldings may be surface degraded. This will affect the ability to re-use such components. FRP claddings and mouldings can be refurbished, by painting for example. FRP components are economical to produce, and this counts against reuse of existing items if they require labour intensive inspection, cleaning, decontamination or repair.

Recycling

Production waste
FRP production waste is generally disposed of since the raw materials used in FRP manufacture are relatively inexpensive (with the exception of aramid and carbon fibres). Quantities of waste produced are usually low in comparison to product volume. If the waste is to be recycled, it may need further treatment such as heat curing before grinding.

Building site waste
Little or no FRP off-cut waste is generated on new-build construction sites. FRP components are designed for a particular use, being pre-moulded and made to measure. This is quite different from the situation with many traditional building components - timber joists, for example, need to be cut down on site from standard sizes.

Deconstruction waste
Current volumes of FRP deconstruction waste are minimal compared to other forms of waste and are presently sent to landfill. However, as the quantities of FRP used in a wider variety of applications increases over the next decade or so, the eventual volumes of post-application FRP will increase. Landfill taxes are predicted to increase sufficiently to discourage disposal and promote reuse or recycling in the future. The FRP industry has to address the situation and identify possible solutions in order to maintain the viability of their products in the construction sector.

There are two main types of resin used for FRPs: thermoplastics and thermosets. Thermoplastic FRPs can be recycled by remelting and remoulding. However, this is not the case for thermoset FRPs which dominate the construction FRP market. One option for thermoset FRPs is grinding, with the resultant recyclate being used as a filler in new FRP materials. Other treatments can be used to return the FRP back to its original constituents in order to reclaim the fibres. One such approach is thermal treatment of the FRP. Thermal decomposition of FRPs has been trialed in order to recover fibres. The FRP (either thermoset or thermoplastic) is heated at temperatures greater than 260ºC (500ºF) which causes the fibres to separate from the polymers5. Another approach is chemical degradation where FRP is placed in chemicals and heated in order to reclaim the fibre. However reclaimed fibres from this process tend to be more brittle because of the chemicals used, which in turn require disposal.

A number of options for the use of FRP recyclate have been identified6. Recyclate could be used for reinforcement in polymer lumber (a reinforced thermoplastic replacement for wood). Recyclate fibre could be used to improve the strength of asphalt, e.g. asphalt for bridge decking, which could possibly accept small amounts of contamination. In speciality Sheet Moulding Compound (SMC), recyclate could be incorporated in between two layers of virgin glass. This process broadcasts the recyclate instead of mixing it with resin. The mixing operation of Bulk Moulding Compound (BMC) can use recyclate, and possibly gains some reinforcement from residual fibres in the recyclate.

Existing FRP recycling pilot plants in countries including France, Germany, Italy and the Netherlands have proved that composite recycling is possible. However, more markets need to be identified for the recyclate produced; few exist at present.

An alternative to traditional FRPs is the development of single-polymer-composites, for example a polypropylene matrix with high strength polypropylene fibres as the reinforcement. This 'all-polypropylene' composite can be recycled resulting in a polypropylene blend that can be reused to remake all-polypropylene composites or can be used for other polypropylene applications. By combining polypropylene honeycombs with polypropylene skins, all-polypropylene sandwich panels with great stiffness can be produced.

Incineration with energy recovery and composting

FRPs have a high calorific value therefore incineration with energy recovery is a viable option for FRP waste.

Incinerator operators actually charge more for accepting FRP waste because the high calorific content together with toxic emissions tends to overload the system, meaning they cannot process as much domestic refuse. It must be borne in mind that the production of electricity from energy recovery is a secondary concern and that the prime business of the incinerator is to dispose of domestic refuse. By burning relatively small quantities of FRP waste, large volumes of domestic waste (of which there is an unlimited supply) must be sent to landfill.

The use of ecocomposites is a growing alternative to FRPs. They use plant fibres as an environmentally friendly and low-cost alternative to glass fibres. Natural fibre FRPs are from renewable resources and can be composted or incinerated at the end of their life. The European automotive industry is investigating the possibility of using natural fibre reinforced thermoplastics to benefit the environment whilst saving weight (natural fibres are 50% lighter than glass fibres) and cost at the same time. Wood flour is also being investigated as an alternative to mineral fillers. These technologies can be used for both thermosets and thermoplastics.

Natural fibres can easily compete with glass fibres in terms of stiffness, but their tensile, compressive and impact strength are relatively low compared to glass fibres. By modifying the resin systems, ecocomposites can be designed to be either stable or biodegradable10. As mentioned above, mechanical recycling is preferred over incineration and landfill. However, mechanical recycling of natural fibre composites could prove problematic as they tend to degrade near the processing temperature of most thermoplastics.

Composting is unlikely to be practicable for combinations of natural fibre and resins such as polyester resin. Plenty of clean plant matter from municipal collection of garden waste, together with agricultural waste such as chicken litter is available for the compost industry to use and building components with difficult to separate organic matter will not be considered.

Incineration without energy recovery and landfill

Incineration without energy recovery and landfilling of composites waste are the least preferred options because they result in a loss of the energy content which could be harvested by incineration with energy recovery. Landfilling of composite waste appears to be the most common disposal option at present in the UK because, although on the increase, the cost of disposal of waste is still relatively low. The fate of surplus new or used FRP components depends on the cost effectiveness of the options available. Thus, until landfill taxes increase to a value where recycling or incineration become viable alternatives, or legislation changes, most of the FRP waste produced will end up disposed of in the ground.

End Products from Recyclate

There are certain criteria which must be met in order for utilisation of waste FRP in a product to be economically and technically viable. Considering ground FRP waste:

• The use of ground FRP should be beneficial to the product i.e. the FRP should have either a structural/reinforcing role or weight saving role, not just act as an inert filler.
• The mix of materials should be synergistic. 
• The product should not have to be reinforced with other material or made thicker to compensate for some deficiency caused by inclusion of ground FRP. 
•  It should not be merely a novel disposal method such as some component of a geotechnical fill.
• The re-use method should be realistic in respect of the likely volumes of recyclate available.
• The re-use of FRP should not make the ultimate recycling of the product difficult (some types of "plastic wood" can be easily recycled or burned without pollution).
• The product should not pose environmental problems or health and safety problems in use - e.g. from abrasion, wear related loss of glass fibres, or during cutting and drilling.
• The product should not be a substitute for something which is actually made from a more sustainable material in the first instance, such as plantation timber.
• The combination of ground FRP with some other waste material should not divert this waste from an existing higher end re-use chain.
• The product should have a suitably long service life.
• The product should be cost effective.

Life Cycle Assessment and Ecodesign

The use of Life Cycle Assessment (LCA) and Ecodesign can aid the construction industry in its search for ecologically friendly products. LCA is a quantitative method to assess the environmental impacts occurring through the product life cycle, covering materials extraction and processing, manufacture, use, disposal and recycling, and has already been applied to the construction industry in the form of BRE Environmental Profiles11. Ecodesign takes into consideration the life cycle of the materials used and the methods of interactions they have with the environment. It looks at reducing the environmental impact of a product over its life cycle without impacting on quality. Ecodesign concentrates on ensuring that products are easier to disassemble and uses mainly components that are more easily reused or recycled. Using these principles in the design process can increase profitability by eliminating waste at the beginning of the product's life cycle rather than at the end.

LCA and Ecodesign can thus feed into any part of the waste hierarchy and are in effect an application of the Best Practicable Environmental Option (BPEO). However, Ecodesign currently lacks the range and detail of information to make an informed decision for all materials and components. Environmental Profiles and LCA data already exist for many recycling and disposal processes, and provide a mechanism to assess new and experimental techniques - due to constraints of time however, these were not explored in this project.

Conclusion

FRPs are increasingly being used in construction due to their low weight, durability and tailor made properties. The UK FRP industry currently produces 240,000 tonnes of product a year with 11% of this being for the construction sector. FRP is widely considered to be un-recyclable, and at present the most common disposal method for such material is landfill. Nevertheless several recycling options have been developed for this material including reintroduction of ground FRP waste into the production process, pyrolysis to generate fuel gas and fluidised bed recovery of glass fibres. Waste FRP has also been used experimentally in the production of wood/plastic composites, road asphalt and concrete. Incineration with energy recovery or in combination with the production of cement is also an option.

Current and impending waste management legislation will put more pressure on the industry to address the options available for dealing with FRP waste. EU waste management directives on landfill, incineration, construction and demolition waste, end-of-life vehicles, electrical and electronic equipment, and UK government policy such as the waste strategy 2000, the sustainable construction strategy, the landfill tax, and local government policy could all influence the FRP industry. Such waste legislation focuses on dealing with waste through the waste hierarchy and will therefore put more pressure on solving FRP waste management through recycling and reuse.

Waste management is becoming increasingly important within the FRP and construction industries, especially with the implementation of EU directives concerning waste management. BRE have an ongoing research programme into waste minimisation and management options, and would like to thank those who have helped so far. BRE are looking forward to future collaborations to assist industry in meeting the environmental agenda.

Further work is needed to examine the effect of contamination of waste streams on end-product properties. Improving the quality of the fibre element of the ground GRP could also be achieved by work on shredder technology.

References

1.  GPRMC Press release - EU Waste legislation becoming more severe, 2001 www.gprmc.be/PressReleases.htm
2.  Hobbs, G. & Halliwell S. 'Recycling of Plastics and Polymer Composites', Composites and Plastics in Construction Conference, Watford, UK, September 1999
3.  Halliwell, S. Advanced Polymer Composites in Construction, BRE Information Paper IP7/99. Garston, CRC, 1999
4.  Hurley, J., McGrath, C., & Bowes, H. Deconstruction and Reuse of Construction Materials. CRC, London, 2001
5.  Jody, B.J.,Daniels, E.J., & Pomykala, J.A. 'Thermal Decomposition of PMC for Fiber Recovery', SPE Annual Recycling Conference, 1999
6.  Simmons, J. 'Recycling Thermoset Composites in North America', JEC Conference, March 2001
7.  George, S.D., & Dillman, S.H. Recycled Fiberglass Composite as a Reinforcing Filler in Post-consumer Recycled HDPE Plastic Lumber. Western Washington University.
8.  Cabrera, N., Alcock, B., & Peijs, T. 'All-Polypropylene Composites for Ultimate Recyclability', EcoComposites Conference, London, September 2001
9.  Peijs, T. 'Markets and Trends in Ecocomposites for Automotive Applications and Beyond', EcoComposites Conference, London, September 2001
10. Riedel, U., Nickel, J., & Hermann, A. 'Bio-composites: State of the Art and Further Perspectives', EcoComposites Conference, London, September 2001
11. Howard, N, Edwards, S & Anderson J, BRE Methodology for Environmental profiles of Construction Products, Components and Buildings. BRE, 1999.
12. Cranfield University & WE&E Consulting. A Brief Guide to Ecodesign.