In the article, “Porous Asphalt Is…,” on the
website Pave Green (n.d), it was stated that porous asphalt is beneficial in
terms of environment, safety and the cost. Porous asphalt earned its
recognition from the Environmental Protection Agency and has been used all
around the United States. It was indicated that porous asphalt roads or
parking lots exclude small aggregates to allow water to pass through,
acting like a filtration system. Thus, this reduces flooding and erosion.
Superhighways also use porous asphalt because it helps to drain water,
improve water quality, removes splashes and significantly reduce accident
rates. The article also mentioned that porous pavement is beneficial in
wintery climates because it allows snow to liquify quicker which saves the cost
of anti-icing agents, making it cost-effective and eco-friendly. Although
the article states that the cost of porous asphalt is higher than conventional asphalt,
the overall cost of construction balances out from the savings made from water
pipes and inlets.
While I agree with the
stormwater management mythology mentioned in the article, “Porous Asphalt Is…,” lacks any concrete information concerning the
constraints and ineffectiveness which has led to the undermining of the article
in naming porous asphalt the “king of the road”.
One characteristic contributing to the ineffectiveness of
porous asphalt that the article has failed
to mention is the critical downside of porous asphalt regarding the risk of
skidding. In the research report, “Experiences with Porous Asphalt…,” Isenring, Koster and
Scazziga (1990) stated that porous
asphalt is not a suitable pavement choice for urban areas because of the low
traffic speed. The same authors explained how the coefficient of friction is relative
to the speed of vehicles and conclude that at higher speeds where the
macro-texture is more important, the pavement will have better skidding
properties. However, at lower speeds where the micro-texture is more relevant,
the skid properties are much lower in comparison to conventional mix. The
article also highlighted that porous asphalt has high macro-texture but low
micro-texture and is exposed to a higher risk in urban roads because of the
densely populated residential areas that created a decrease in traffic speed.
Having low speed, the inadequate micro-texture will cause more skidding cases
in urban areas especially in wintery climates.
Another negative aspect that was not mentioned in the original article is
that porous
roads require frequent maintenance and is problematic in urban areas due to the
high traffic conditions. Isenring, Koster and Scazziga (1990) also mentioned that continual
maintenance, it will contribute to a decrease in the permeability and porous
asphalt will lose its noise reduction capability. Thus, the noise problem in
urban areas generally cannot be solved with the use of porous asphalt. The same authors also mentioned that unlike the
conventional mix, the binder coasting of the porous asphalt will have to be
worn off before it can achieve its intended efficiency. Furthermore, porous
asphalt at its pre-binder coasting state has even poorer micro-texture and normal
repairing methods such as spreading of chippings will not be able to improve
the situation.
Lastly, GreenBlue (2017) also state
that porous asphalts will clog easily if no proper maintenance and regular checks
are made. The void spaces in between the pavement can be clogged by fine
particles and sands and can only be removed using an industrial vacuum. Without
fast maintenance, the permeability will decrease causing water and other
pollutant to run off the surface which defeats the purpose of having permeable filtering
pavement. The article also mentioned that the strength of porous asphalt cannot
compete with traditional pavement. With consistent pressure from dynamic
loadings such as heavy vehicles, it will cause pores of pavement to collapse. As
a result, porous asphalt is not a recommended pavement for highways and airport
runways.
In summary, the article by Pave Green
(n.d) came across to me as being biased in the
favor of porous asphalt as it only addresses the advantages. Porous pavements
are not as perfect as it sounds, and like many other sorts of pavement, it has
its own limits and restrictions and can only do so much.
References
Green Blue. (2017, January
25). Permeable Pavement: The Pros and Cons You Need to Know. Retrieve from https://www.greenblue.com/na/permeable-pavement-the-pros-and-cons-you-need-to-know/
Isenring, Koster, Scazziga. (1990). Experiences with Porous Asphalt in
Switzerland. Retrieved from
http://onlinepubs.trb.org/Onlinepubs/trr/1990/1265/1265-005.pdf
Pave Green. (2018, February 5) Porous
Asphalt Is King of Road. Retrieved from http://www.pavegreen.org/index.php?option=com_content&view=article&id=58:king-of-the-road&catid=35&Itemid=110
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