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. 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 melt 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 environmental
aspect of stormwater management mentioned in the article, “Porous Asphalt Is…,” the article 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 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 decrease
in traffic speed due to the densely populated residential areas. When vehicles
travel at low speed in urban areas, 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 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/
Thomas, I., Harold, K., & Ivan, S. (1990).
Experiences with Porous Asphalt in Switzerland. Retrieved from https://trid.trb.org/view/348603
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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