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Use of Fuel Resistant Asphalt for Aircraft Pavement
surfaces in Australia
Greg White1
Abstract
Many regional and smaller airport aprons in Australia and provided with an
asphalt surface course. In areas where fuel spills from venting aircraft tanks
and refueling operations are unavoidable, the surface is exposed to
hydrocarbons on a regular basis. Bitumen binders are softened by these
hydrocarbons and the surface can be damaged. Such damage can lead to
increased maintenance effort being required and increased loose material on
the apron surface which, can be ingested and damage aircraft engines.
Traditionally in Australia aircraft parking aprons were treated with a fuel
resistant membrane. These membranes are sprayed onto the surface some
weeks after asphalt finishing. Such membranes, generally tar-based
products, result in top-down cracking of the asphalt and require re-treatment
every two to three years.
Shell Bitumen has developed a fuel resistant asphalt binder, Mexphalte
Fuelsafe. This material is a proprietary product which blends a mix of
polymer products into conventional bitumen. This fuel resistant binder offers
the advantages of not resulting in top down cracking and being more
economical than fuel resistant membrane treatments. The resulting asphalt
has a stiffness that exceeds that from conventional binders and is easily
manufactured.
A field trial at an Australian Defence airfield demonstrated that the fuel
resistant asphalt was manufactured, placed, compacted and finished like
conventional asphalt. The only noticeable difference being that the asphalt
had a slightly sticky feel which caused some adhesion to the screed at the
rear of the asphalt paver. Twelve months after construction and following
significant fuel exposure, the apron surface is performing well.
Otherwise identical cores of asphalt containing conventional and fuel resistant
binders were taken from the trial and assessed. Based on surface exposure
and submersion in diesel fuel for 10 days, it was concluded that the fuel
resistant binder resisted hydrocarbons for a few days. However, after
prolonged exposure the hydrocarbons were absorbed by the asphalt. Once
hydrocarbons were absorbed, the fuel resistant binder softened in a similar
manner to the conventional bitumen. It was concluded that the fuel resistant
binder was therefore effective in resisting short term fuel spills but would be
less effective under prolonged or continuous spills in an isolated area.
1 Senior Pavement Engineer with consulting engineers Sinclair Knight Merz, based in
Brisbane, Australia.
Introduction
Fuel spills of a minor nature are generally considered to be inevitable on
aircraft pavements where parking and refueling occurs. Many nozzles used
for refueling retain some fuel at the completing of refueling and this is often
spilt on removal of the nozzle. Other aircraft frequently vent fuel on engine
start-up or shut-down.
Some airports have adopted concrete pavements or segmental concrete
block surfaced pavements for refueling areas. However, this is not always
feasible or economical. Where refueling is performed on asphalt surfaced
pavements, a fuel resistance coating has commonly been applied to retard
the rate of erosion and degradation of the asphalt as a result of hydrocarbon
damage.
Use of fuel resistant asphalt binder as an alternate to traditional asphalt
binder and a fuel resistant membrane is presented. A number of field trials
are described as well as the results of preliminary testing of asphalt
manufactured with traditional and fuel resistant binders.
Traditional Approach
Prior to tar based products becoming recognized as carcinogenic at elevated
temperatures, tar binders were used in asphalts subject to fuel spills. While
many of these pavements have now been reconstructed or overlaid with
conventional asphalt, some remain in service and remain very resistant to fuel
damage. When tar asphalts are overlaid, the texturing of their surface by
profiling machine can be hazardous. The profiling machine heats the asphalt
surface and is suspected to create potentially carcinogenic fumes.
Without the ability to use tar based binder for fuel resistant asphalt, efforts
turned to the development of fuel resistant membranes that were applied to
the surface of conventional asphalt layers. These membranes are generally
coal tar based or acrylic products, and are applied cold as emulsions. A
number of proprietary products are available and these include:
• Jetseal. By Boral Asphalt.
• Pavron. By Swepdri International.
• Superseal. By Australian Pavement Maintenance Systems.
• Bitulastic Roadseal. By Bituminous Products.
• Viroseal AB. By Slip Resistant Surfaces.
• Sealmaster Coal Tar Concentrate. By Sealmaster.
One of the advantages of these materials is that they can be applied to small
and irregular areas without the need to treat an entire apron. However,
significant limitations have been observed with these materials in recent
times, as described below.
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Softening of asphalt
Where a new asphalt surface pavement is constructed or an existing apron is
provided with an asphalt overlay, fuel exposure will commence on returning
the area to active service. If application of the fuel resistant membrane is
significantly delayed, the new asphalt surface can be damaged by fuel
exposure. However, if the fuel resistant membrane is applied within the first
six weeks after asphalt resurfacing, the hydrocarbon based emulsifier can
also soften the asphalt surface, leading to scuffing under aircraft traffic.
Figure 1 shows scuffing of asphalt softened by the early application of a coal
tar based fuel resistant membrane at Newcastle Airport.
Figure 1 Scuffing of asphalt at Newcastle Airport
Cracking of asphalt
Due to the nature of the tar-based products, they shrink after application. The
fuel resistant membrane’s integrity is then lost and any spilt fuel can enter the
cracks and affect the asphalt below the surface. A typical cracked membrane
is shown in Figure 2. Commonly, these membranes will be replaced every
two to three years and the cumulative effect of the shrinkage and cracking
can crack the underlying asphalt. In some circumstances, cracks have been
observed to extend through the full depth a of 50 mm asphalt surfacing as
was the case at RAAF East Sale in 2006. In such circumstances, the asphalt
surface generally requires full depth replacement.
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Figure 2 Cracked fuel resistant membrane at Cairns Airport
Slippery surface
Some products have been found to be slippery under foot after application.
When wet, they have been reported to be an OHS hazard to aircraft ground
staff. Figure 3 shows a very slick and slippery surface after treatment with
Viroseal AB at RAAF Edinburgh.
Figure 3 Slick and slippery surface at RAAF Edinburgh
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Fuel Resistant Binder
In an attempt to alleviate some of the problems associated with fuel resistant
membranes, a fuel resistant binder was considered as a replacement for the
historically popular tar asphalt.
Kuala Lumpur International Airport was the first airport known to have
specified fuel resistant asphalt for their flexible pavements. Ooms Avenhorn
Holding from The Netherlands developed a Polymer Modified Binder (PMB) to
be resistant to softening under fuel exposure for this project (Rooijen, et al,
2004). When compared to conventional Superpave binders, the Ooms
Avenhorn Holding product demonstrated:
• Reduced increase in deformation under load following 24 hours fuel
immersion.
• Reduced increase in penetration following 24 hours fuel immersion.
• Reduced loss of mass by wire brushing after 24 hour and 72 hour fuel
immersion.
Since the Kuala Lumpur project, the Ooms Avenhron Holdings product has
been used at other international airports including Cairo (Egypt) and La
Guardia (New York) (Corun, et al, 2006).
Nyguard is a equivalent product available in the United Kingdom, developed
by Nynas Bitumen (Materials World, 2004). This product was used for the
resurfacing of two runways at Bristol International Airport in 2004 and was the
first reported use of such a product in the UK. This product is also a
bituminous binder containing a blend of polymer additives.
In Australia, a comparable product has been developed by Shell Bitumen.
Shell’s Mexphalte Fuelsafe (Shell, 2006) is also a PMB. The combination of
polymers has been designed and selected to maximise the product’s ability to
resist fuel damage whilst maintaining workability and other performance
characteristics similar to conventional and common PMB products.
Table 1 summarizes the results of laboratory testing of dense graded asphalt
sampled manufactured with Mexphalte Fuelsafe and conventional C320
bitumen.
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Table 1 Comparison of Mexphalte Fuelsafe and C320 binder
Property Units
Mexphalte
Fuelsafe Conventional
C320
Weight loss after
immersion in diesel % loss by mass After 1 day <1
After 7 days 2
After 1 day 6
After 7 days 18
Weight loss after
abrasion testing grams No immersion 10
After 1 day 35
After 7 days 55
No immersion 25
After 1 day 55
After 7 days 305
Deformation at
40 C % deformation 1.1 3.2
Allowable initial
strain for for fatigue
at 1,000,000 cycles
µm/m 170 111
Based on the results presented in Table 1 it was considered that Mexphalte
Fuelsafe would provide increased resistance to fuel exposure when
compared to C320 binders. It was also concluded that even in non-fuel
exposed areas, Mexphalte Fuelsafe can offer increased resistance to
deformation and increased resistance to fatigue compared to C320 binder.
Discussion with Shell Bitumen technical staff determined that the Mexphalte
Fuelsafe could be utilised as a direct substitute for conventional binder in
asphalt. Shell Bitumen staff also advised that the asphalt mix would have
similar workability characteristics to the same asphalt mix containing a
conventional binder.
Field Trials
Based on the success of similar materials in other countries, a number of
projects were selected as trials of Mexphalte Fuelsafe in Australia. The first
known use of this material was on an aircraft parking apron at RAAF
Amberley, near Brisbane. No formal monitoring of the resulting surface was
located. SKM specified Mexphalte Fuelsafe, as a direct replacement for
C320 conventional binder, on apron resurfacing projects at RAAF East Sale
(west a Melbourne) and RAAF Williamtown (near Newcastle). Both projects
were constructed from May to July in 2006. Table 2 presents a summary of
known Mexphalte Fuelsafe use in Australia.
Table 2 Mexphalte Fuelsafe use on Australian Airports
Airfield Area Dates Quantity of asphalt
RAAF Amberley Air Movements Apron April 2005 600 tonne
RAAF East Sale King Air Apron May 2006 1600 tonne
RAAF Williamtown Air Movements Apron June 2006 2400 tonne
Constructability
No significant constructability issues were identified with the Mexphalte
Fuelsafe binder. The asphalt was, however, observed as being stickier than
asphalt with conventional binder. This stickiness resulted in occasional
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dragging of asphalt mat when it passed the screed at the back of the paver.
This dragging was minor and did not significantly affect the resulting asphalt
surface. The stickiness also added minor inconvenience to hand work where
the asphalt frequently stuck to shovels and lutes. Densities achieved with the
Mexphalte Fuelsafe were equal to or better than those achieved for the C320
binder (Emoleum, 2006).
Field Performance
The work at RAAF East Sale included asphalt with Mexphalte Fuelsafe as
well as C320 binders in adjacent areas. Apart from the binder used, the
asphalt mixes were identical in their design. This allowed a direct comparison
of the two products in the same aggregate matrix, manufactured from the
same plant and constructed at the same airfield, in virtually identical locations
and environments.
The most heavily fuel exposed area of the RAAF East Sale apron is the King
Air parking positions. The refueling nozzles eject excess fuel at the
completion of the refueling operation so regular small fuel spills are expected.
The asphalt in these parking positions was re-inspected one, three and six
months after construction. Despite significant evidence that fuel had been
spilt in these areas, the asphalt was essentially unaffected as shown in
Figure 4.
Figure 4 Fuel exposed Mexphalte Fuelsafe asphalt
Material Testing
A number of cores were taken from the Mexphalte Fuelsafe as well as from
C320 asphalt during the RAAF East Sale work. The asphalts were otherwise
identical in design. Four cores were subjected to fuel exposure and
monitoring over a period of 10 days at SKM’s Canberra office. Diesel was
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used as a proxy to aviation fuel and two samples (one of each binder) was
semi submerged in fuel to a depth 2/3 the height of the sample, whilst the
other two (one of each binder) were provided with a ring of silicone sealant to
retain the fuel and fuel was added to the surface only, at a rate of 0.1 mm of
fuel every day for 9 days. The samples are shown in Figure 5. The samples
were monitored on a daily basis and intermittently the surface exposed
samples were brushed in isolated areas to determine the extent of surface
softening. A summary of the observations from this experiment follows:
• The relative performance of Mexphalte Fuelsafe and C320 was essentially
the same for both the semi submersed and surface exposed samples.
• During the first few days of exposure, the Mexphalte Fuelsafe sample
resisted penetration of the diesel and the fuel pooled on the surface on
application. The C320 sample absorbed the fuel almost instantly.
• After five days of exposure, the Mexphalte Fuelsafe absorbed newly
applied fuel as quickly as C320.
• Both Mexphalte Fuelsafe and C320 samples were easily eroded by
abrasion with a toothbrush at the completion of exposure. The C320
samples were more eroded and the semi submerged sample failed under
its own weight when removed from the fuel bath. Figures 6 and 7 show
samples following fuel exposure.
Figure 5 Fuel exposure samples before testing
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(a) Fuelsafe sample after seven days immersion.
(b) C320 sample after seven days immersion.
Figure 6 Samples following seven days immersion in diesel.
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(a) Fuelsafe sample after seven days surface exposure.
(b) C320 sample after seven days surface exposure.
Figure 7 Samples following seven days surface exposure to diesel.
Based on the testing performed and monitoring of the samples over time, it
was concluded that during the early stages of fuel exposure, the Mexphalte
Fuelsafe demonstrated significantly improved fuel resistance properties when
compared to C320 samples. However, the difference in performance
narrowed as fuel exposure become prolonged. Additional laboratory testing
is recommended to determine the true comparative fuel resistant of
Mexphalte Fuelsafe and other binders.
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Cost-Benefit Analysis
Based on the 1 September 2007 price list from Shell (Shell, 2007) the price of
one tonne of bitumen in Brisbane is $665 for C320 and $979 for Mexphalte
fuelsafe. Given that airport asphalt typically contains 5.5 to 6.0% binder, this
would result in around $18/tonne difference in the cost of asphalt. Based on
a density of 2,400 kg/m3 and a thickness of 60 mm, this converts to a cost
difference of around $3/m2.
A cost benefit analysis of Mexphalte Fuelsafe versus a conventional C320
binder with a fuel resistant membrane was performed. The analysis was
performed based only on capital cost as the comparative long term
performance is currently not known due to the short period of time that the
Mexphalte Fuelsafe binder has been available for. The cost benefit analysis
is presented in Table 3 and is based on typical asphalt surfacing cost for
60 mm of 14 mm mixed asphalt. Based on capital cost alone, Mexphalte
Fuelsafe has significant economic advantage over C320 binders where a fuel
resistant membrane would be required. Further assessment of the whole of
life cost of various binder options in fuel exposed areas is recommended once
the life cycle of Mexphalte Fuelsafe asphalt is determined.
Table 3 Cost benefit of Mexphalte Fuelsafe and C320 binder ($/m2)
Assumed life Mexphalte Fuelsafe Conventional C320
Asphalt cost $25 $25
Additional cost for binder $3 -
Fuel Resistant Membrane - $8
Total $28 $33
Conclusions
Since the phasing out of tar binders in asphalt, the application of a fuel
resistant membrane to asphalts containing C320 binder has become the norm
for asphalt exposed to fuels on airport aprons. With the introduction of
Mexphalte Fuelsafe by Shell Bitumen, a new option is available for these
areas.
Based on literature and the limited test data available, Mexphalte Fuelsafe is
concluded as being suitable for direct replacement of C320 or other
conventional binder in airport asphalt mixes. The stiffness and deformation
resistant of this polymer modified binder exceeds that of conventional binders.
From the experience of three asphalt overlays, including RAAF East Sale
where both Mexphalte Fuelsafe and C320 were used in the same asphalt mix
on adjoining pavement areas, the Mexphalte Fuelsafe appears to present no
significant construction issues. The only minor issue being its tendency to
stick to the paver screed and hand tools. Field performance also appears to
be satisfactory for the three trials performed to date, where exposure to fuel is
not severe. It is recommended that these trials be monitored over the life of
the asphalt to confirm the field performance of the binder. It is considered,
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however, that Mexphalte Fuelsafe will not perform as well under severe fuel
exposure as tar asphalts did in the past.
From limited testing, Mexphalte Fuelsafe appears to have significantly
improved fuel resistant properties under limited of short term fuel exposure.
This improved performance appears to narrow after longer term or repeated
exposure. It is recommended that a more formal laboratory testing regime be
undertaken to further determine the short and long term benefits of this
material over C320 and other binders.
The capital cost of Mexphalte Fuelsafe is greater than for conventional
binders. However, when the cost of applying a fuel resistant membrane to
the conventional binder is taken into account, the capital cost of Mexphalte
Fuelsafe becomes very favorable. It is recommended that the comparison of
capital cost be extended to consider whole of life cost once the life cycle of
Mexphalte Fuelsafe asphalt is determined from observation of the field trials.
References
van Rooijen, R. C., de Bondt, A. H., and Corun, R. L. (2004). ‘Performance
evaluation of jet fuel resistant polymer-modified asphalt for airport
pavements’. In Proceedings 2004 FAA Worldwide Airport Technology
Transfer Conference. Federal Aviation Administration of the USA. New
Jersey, USA. April.
Corun, R., Van Rooijen, R. C. and de Bondt, A. H. (2006). ‘Performance
evaluation of jet fuel resistant polymer-modified asphalt for airport
pavements’. In Proceedings 2006 Airfield and Highway Pavements Speciality
Conference. American Society of Civil Engineers. Atlanta, USA. May.
Materials World. (2004). ‘Asphalt Surfaces Designed to Resist Fuel for use
in Runways’. Materials World. Vol 12. No 8. Pp 15-16. August. 2004.
From www.azom.com/details.asp?/ArticleID=2589 accessed 14 November
2006.
Shell. (2006). Shell Mexphalte Fuelsafe. Product brochure. Shell Bitumen.
Emoleum. (2006). Materials Test Reports. Emoleum Thomastown
Laboratory. RAAF East Sale PMP Bitumen June. 2006. Thomastown,
Victoria.
Shell. (2007). Bituminous Products Price List. 1 September 2007. Shell
Bitumen.
Acknowledgement
The author would like to thank his employer, Sinclair Knight Merz, for
supporting the preparation of this paper and attendance at this conference.
The assistance of Shell Bitumen in providing information regarding Mexphalte
Fuelsafe is also acknowledged.
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