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INTRODUCTION:

Porous asphalt is a developed type asphalt that the water can penetrate the full depth of the structure; very high-interconnected void within the pavement structure allows the water to flow smoothly. The main advantage of porous asphalt pavement is to enable the water to penetrate the pavement to decrease the surface runoff, dissipate tire noises, provide a good skid resistance because the surface texture is relatively coarser than conventional asphalt concrete, and eliminate specular light reflection under wet pavement surface and decrease spray and splashing during rainfalls. The mixture manufactured from the open graded aggregate with macadam bituminous. Maximum aggregate size should not larger than 20-mm, typically maximum aggregate size 14-mm suit with excellent porous structure, the minimum aggregate size should not smaller than 8-mm. Some fine material (Filler or coarse sand) added to the mixture depending on the desired permeability rate of the pavement; Low fine content higher porosity can achieve and vice versa. The large percentage of voids remain unfilled because low binder content used, the binder should be stiff as much as possible to avoid filling open pores when the bitumen was hot, sometimes rubber modified bitumen used to achieve stiff bitumen binder.

Fig.1 Porous Asphalt (Source: Arroyo Mocho Trail)


The pours pavement designed to self-drain the water out of the pavement structures, the lower part of porous pavement placed over the channel or placed on filter layer of cobbles or coarse aggregates, and then the water can drain out by collector pipes inside the filter layer.
Porous pavement has the following negative points:


1- The permeability is decrease alongside pavement lifetime because the pavement usually compacted under traffic and this compaction leads to damage interconnected pores.


2- The large number of voids filled by dirt and debris, it can’t clean easily, for that reason the lifetime of porous asphalt estimated 8-10 years (Lavin, 2003), the porous asphalt shouldn't use for some areas which polluted runoff water is presence to eliminate clogging (Diniz, 1980).

3- The permeable pavement is relatively expensive than other conventional asphalt pavements, because of its need special staff, the special grade of aggregates, and stiff bitumen.


4- The strength is lower than the conventional asphalt pavements, because the large percentage of the pavement structure consists of open pores, and thin asphalt films used to coat the aggregate (Diniz, 1980).


5- Freezing can occur easily because the pores are open to atmosphere; if freezing occurs after water penetrates into the pavement, the volume of water increased and pushing the pavement surface up, this phenomenon called "Mushrooming" (Lavin, 2003)


REFERENCE:

1- Lavin, P. (2003). Asphalt Pavements. 1st ed. London: Spon Press.

2- Diniz, E. (1980). Porous pavement. Cincinnati, Ohio: Municipal Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency.


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WRITER PROFILE:-

BALEN ZRAR ABDULSAMAD

BSc- Geotechnical Engineering\Koya University

MSc- Infrastructure Engineering\ Szechenyi Istvan University


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