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 cost of porous asphalt is higher, 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…,” it lacks any concrete information concerning its constraints
and ineffectiveness which has led to the undermining of the article in naming porous
asphalt the “king of the road”.
Firstly, the article has failed to mention one critical downside of porous
asphalt regarding the risk of skidding. In the research report, “Experiences
with Porous Asphalt…,” Isenring (1990) has proved the incapability of porous
asphalts in urban areas with the aid of the skid trailer Skiddometer BV8. From
the same article, figure 3, it shows a graph which explains how the coefficient
of friction is relative to the speed of vehicles. It concludes 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.
Secondly, Isenring (1990) also mentioned that porous
roads require frequent maintenance and is problematic in urban areas due to the
high traffic conditions. Without 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. Isenring
(1990) 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
pollutants 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 loading 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:
1. 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
2. Isenring, Thomas. Harald, Koster. Ivan Scazziga. (1990). Experiences
with Porous Asphalt in Switzerland. Retrieved from
http://onlinepubs.trb.org/Onlinepubs/trr/1990/1265/1265-005.pdf
3. 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/
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