1. Introduction
As we are aware, the challenge facing the world is lowering its carbon emissions. This was first internationally recognized in the Kyoto Protocol agreement of 1997, which states that countries must lower their GHG (greenhouse gases) emissions or penalties will be incurred.
The construction industry makes up 22.3% of carbon emissions according to the European Commission for Emissions document, with the energy sector still emitting more (38.2%) and transport at 23.1% (European Commission, 2010). There are options to make this better for construction even in times of financial difficulties but this must be done as a personal responsibility, in order for change to occur globally. The United States of America is the largest carbon contributor, emitting 25.2% of all emissions, China is second with 15.2% then Russia with 6.7% and other industrial countries such as Japan, India, Germany and the UK not producing more than 5% (Nation Master 2010). However, this is justified by their size and populations as well as their contribution to the global economy.
Steel is widely used in the construction industry and in the year of 2011, it was predicted that 1306mmt (million metric tonnes) would be used, a record level (Recycling Portal 2010).
DURABILITY AND SUSTAINABILITY OF FIBRE REINFORCED POLYMER (FRP) COMPOSITES FOR CONSTRUCTION AND REHABILITATION
Steel has a high carbon footprint, in particular high yield steel, which is preferred in construction, due to more carbon being used to produce a high yield strength and FRP carbon emissions are less than that of steel. Therefore, the continued trend of FRP rebar being used in preference to steel will lower our carbon emissions over time in construction.
The life cycle costing must be equal to, if not less than that of steel for FRP to seriously make a difference to industry. A negative aspect of some FRP production in terms of materials is the polymer manufacture, which can be made from fossil fuels. However, FRP contains the polymer, polysiloxane. Which is vastly abundant and easily synthesized from siloxanes. Although this is greatly negative for some FRP, we must not only look at the long-term benefits of FRP, with respect to carbon emissions.
As well as the direct benefits of FRP, there are indirect benefits with construction, such as incorporating FRP with concrete. The light weight rebars and a higher tensile capacity allows for lighter weight structures. This in turn provides for less concrete and less cover is necessary to protect the rebars from aggressive environments.
2. Aspects of Importance for Sustainability
Sustainability has evolved in meaning over the years. The original definition was coined as development that meets the needs of the present without compromising the ability of future generations to meet their own needs’, stated in the Brundtland report in 1987 (World Commission on Environment and Development (WCED), 1987). In essence, sustainability must protect the present and the future; therefore the following aspects have been identified as important in this paper:
2.1 Economy and Life Cycle Costing
Construction accounts for 30.6% of GDP worldwide (CIA, 2010) and therefore, has a massive influence on the world economy. FRP continues to get cheaper and with greater developments being continually made to FRP to make them better in construction. That said it is still more expensive than Steel (Burgoyne and Balafas, 2007). With that in mind, can FRP be economically more viable that steel? We should not disregard FRP because the cost of manufacture is greater than that of steel, as the life cycle costing and other ‘hidden’ costs, (such as for repairs) are not included. FRP also gives the opportunity to design for specialized buildings with longer life spans, and many research papers have concluded that the life cycle costing for FRP is more beneficial for FRP as seen in Nishizaki’s research. Nishizaki concluded that although the initial costs are high, when longer life spans are necessary FRP is an efficient choice of material (Nishizaki et al., 2006).
2.2 Properties
The very properties of FRP make them sustainable. Polysiloxane, the polymer commonly used for FRP, is an inorganic polymer which is already oxidized due to the Si-O bond and consequently does not suffer from oxidation effects, unlike steel. This property in turn allows for a much greater service life and lower maintenance with fewer necessary repairs. Moreover, Polysiloxane’s have high resistance to UV light and temperature (Norman R. Mowrer, 2003).
CFRP, GFRP and BFRP all have the same if not greater tensile capacity in comparison to steel. They are also lightweight (lighter than steel) and have specific stiffness; these properties add to the repertoire for FRP being good to construct with. The recent studies into chemical testing with BFRP has shown great resistance to acid and alkali resistance. This inertness is a great property to ensure longer life spans of structures. The high resistance to temperature has also made BFRP a choice in structures for
enhancing the fire resistance of structures as commented by Matthys et al (2009).
2.3 Construction Phases
There are definitive phases that a construction material must go through in its life. These are: Manufacture, construction, mid-life and life expansion and end of life as commented by Burgan and Bassam (2006); these are discussed in relation to FRP usage.
2.3.1 Manufacture
FRP rebar is undoubtedly more difficult to manufacture than steel at present. However, the carbon emissions and the impact to the environment are less with FRP. Steel contributes greatly to carbon emissions and temperatures of a little under 1400°C are required constantly, therefore large amounts of energy are used. In order to manufacture Glass, Carbon and Basalt fibers, temperatures of up to 2400°C are used (Lee and Jain, 2009), which is greater than steel, but currently less FRP is being made and the process of manufacture is continually being refined. Both FRP and steel rely on fossil fuels to be burnt (Gerdeen et al., 2006), which are not in infinite supply and this is of concern as Lee and Jain (2009) point out in their paper outlining the role of FRP. The abundance of Siloxane (which is any compound containing R2SiO) and Basalt (volcanic rock) for BFRP, make BFRP a particularly sustainable choice of FRP for the future as well as the products necessary for CFRP and GFRP.
FRP contain a greater amount of chemicals in order for the composition to be made as seen in the table 1.
Some of these chemicals are rare (Ti for example) and can be hazardous, but for BFRP and GFRP they are naturally found in the production of the compounds and therefore not added. Also, when controlled they are no greater a threat to the environment than the by-products of steel (carbon as for CO2 a GHG and unwanted products from the slag).
As for the abundance of materials glass fibers (as SiO2) for FRP (in particular GFRP) are in great supply and is easily manufactured using thermosetting plastics such as unsaturated polyester. Carbon for CFRP too is sustainable to reuse in construction and is greatly available from graphite. Basalt Fiber is made by the direct extraction of basalt rock (volcanic) from selected quarries. The rock is then crushed into an extremely fine dust. This basalt dust is then attached to the polysiloxane polymer, thus reinforcing the polymer. With this argument of materials being in abundance the same can be argued for steel as iron is the 4th most abundant element of the planet, although the manufacture of steel could be seen to be more harmful to the environment, as the materials required for FRP are more readily available than smelting steel from the extraction of iron ore.
2.3.2 Construction
The single greatest disadvantage for FRP has been the lack of design codes. Burgoyne and Balafas stated in 2007 that this was a main contributor to why FRP is not a financial success. Taketo Uomoto (2007) also agreed that efforts needed to be made for design codes for FRP and this would mean greater ease and use of FRP in buildings and not just as an alternative material.
Indeed, great efforts have now been made and there are now design codes in many countries such as America (although a Eurocode is now been developed) and this is due to the continual interest in FRP as seen in all research and specifically the document ACI 440.1R-06 (Ospina and Gross, 2006). The lack of sufficiently developed design codes has not stopped engineers building with FRP, however, and indeed the properties of FRP compliment the building industry well. Their lighter weight makes the construction process safer, boosting the construction industries poor health and safety record. This also boosts the construction time of buildings as seen by (Lee and Jain, 2009). The UK has seen this directly with domes and mosques been made in cheaper and faster fashion (Kendall, 2007).
2.4 Midlife and life expansion
Life expansion is easy with the rebars as other external FRP can be retrofitted which mirrors the structural behavior of the internal rebars. The properties of FRP compliment strengthening t buildings in need of repair and this has been a market that has greatly boosted the use of FRP. It is always of benefit to extend the service life of a structure as far fewer resources are required than to demolish and re-build. This compliments the ideology of sustainability with reuse of buildings. FRP also do not require methods like cathode protection due to their inertness to corrosion and would only require standard monitoring techniques with sensors and monitoring the deflection of the beam in order to ensure that the beam is not failing.
2.5 End of Life and waste
With rebars there is very little waste as the design is established well before the build so the amount used is the amount ordered (waste minimalization). That said, the waste of FRP becomes an issue in demolition. Steel offers benefits that FRP in general does not; steel is readily reusable and recyclable and there are large businesses that specialize in this. Steel is easily processed from the waste concrete and then recycled, but the reprocessing of steel also produces CO2 emissions. FRP can also be reused in other aspects such as crushing it down into aggregate (dispersed reinforcement). Patents have now been passed for the recycling of waste FRP, as seen by (Kamite et al., 2008) and this is a major step of many to come for the recyclability of FRP. There are other methods of using chemical substances to break down the resin from the polymers, however this is an expensive and hazardous solution, but with waste of plastics
being a growing problem there are many initiatives in to process FRP.
The main issue with recycling and therefore reusing FRP is the way in which they are manufactured, as identified by Bartholomew (2004). FRP are highly engineered polymers designed for long lifespans. Therefore, they demand high amounts of energy (as they have high calorific values) making incineration with energy recovery troublesome to the operators as well (Halliwell, 2009). FRP waste is in general non-hazardous, however only the dust particles (which are only produced in cuttings during the manufacture stage) have been studied in laboratory conditions and have been seen to be harmful, although much less in comparison to other construction materials (Hesterberga et al 2010; U.S. Department of Health and Human Services, Public Health Services, Agency for Toxic Substances and Disease Registry, 2004).
FRP waste according to the European waste list 2000/532/EC, is classified under several codes (CEFIC Tecnical Bulletin, 2006) and these must be known in order to organise waste correctly and legally in Europe. Possibly the most commonly used for construction purposes at the demolition stage would be CEFIC – 17 02 03. However, this would depend on the state of the FRP; as stated before it can be classified into Hazardous waste ‘within the H1 to H14 list of Annex III of EC Hazardous Waste Directive (CEFIC Technical Bulletin, 2006).
Halliwell’s paper on Recycling FRP materials, comments on FRP being difficult to reuse, as it is difficult to ascertain the loading properties of pre-used FRP beams, and this can be a lengthy process. FRP waste is also predicted to double, from some 156,000t being used in 2000 to a predicted 304,000t in 2015 (Harbers, 2002).
Conclusions
FRP is a material that has the capacity to allow for greater service life and greater life cycle costing for construction of structures. FRP are cost effective in many aspects, have higher strengths, greater resistance to aggressive environments and are sustainable in our current global environment. Certainly, FRP have their disadvantages in comparison to steel; they are not readily reusable and there is no established design code in the EU. The finalization of the design code worldwide and standardization of FRP materials will ensure the future of FRP. In terms of manufacture, FRP offers great sustainability and great promise to the world of construction.
Assessing the Recycling Advantage
While FRP can be recycled, it is not usually economically feasible currently. However, in most of the applications studied to date, production of virgin FRP parts actually consumes less energy and produces less greenhouse effect than recycling of steel and aluminum. For instance: A study comparing the energetic values (exergy) of various material options for construction of a pedestrian bridge yielded these results:
A Life Cycle Inventory (LCI) study of steel, aluminum and FRP composites, in a number of applications also indicated a clear advantage in energy usage for composites over recycled steel and from near parity to clear advantage over recycled aluminum.
Plasti-Fab Recycles and Reuses Fiberglass in Composites Manufacturing. Composites Week, No. 14, Vol. 12, April 5, 2010.
Daniel, Ryszard A., Environmental Considerations to Structural Material Selection for a Bridge. European Bridge Engineering Conference, Rotterdam, March 2003.
Jakubcin, Gary – LCACP. A Life Cycle Assessment Approach in Examining Composite Raw Materials, Steel and Aluminum Materials Used in the Manufacturing of Structural Components. Report prepared for Strongwell, Inc., June 19,2009.
The LCI did not include energy required for the pultrusion of composite material (small), the re-melting, rolling and fabrication of recycled aluminum ingots (large) nor the shaping and cutting of recycled steel plate for required parts (moderate). In general, including all energy required for each material is believed to further favor composites.
Data for 100% recycle aluminum extrapolated from that for 0%, 50% and 80% cited in the report.
Calculated as 75% of energy required for steel production cited in the report.
“Green” Relationships
The following diagram represents the relationship to various “Green” issues.
“Green” Manufacturing Initiatives
To further reduce the overall environmental footprint of FRP composites, conservation improvements are underway within manufacturing. These have already yielded significant reductions in the usage of energy, solvents and landfill capacity, along with reduced generation of scrap, waste and emissions.
The Future
ACMA are confident that expanded studies currently underway will continue to demonstrate that FRP composites are exceptionally eco-friendly. Bio-resins and natural reinforcement fibers are now available and are beginning to appear in some new products. Continued research by resin and reinforcement manufacturers is expected to result in additional options for the FRP industry to further improve its position as the preferred GREEN solution for construction materials. We believe that FRP composites are already the best choice for reduced environmental impact, longer service life, and greater sustainability. And, unlike metals which have little potential for improvement, FRP materials will become even better.
