Porous asphalt

PA is a bituminous mixture with a high content of interconnecting voids that allow passage of water and air in order to provide the compacted mixture with drain and noise-reducing features. It is used for surface courses and it can be laid in one or more than one layer. 

PAs were developed during the 1960s in England, initially for airfield surface courses in order to eliminate rainwater, thus preventing aquaplaning. Successful full-scale trials on roads application led PA to be used in highway pavements as well (Brown 1973 Daines 1992 Nicholls 1997). Since then, other countries started to apply PA as a surfacing course. PA can successfully be laid over concrete surfaces (Nicholls 2001). 

The paradox is that although PA was developed in England, PA became more widespread in other countries. PA is widely used in Holland, Switzerland, Italy and Spain. The PA production percentage amounted to 13% of the annual production for hot and warm mixtures in 2010 in Holland. The corresponding figures for the rest of the abovementioned countries were 8%, 5% and 2% (EAPA 2011). From the same source, the corresponding figure for Japan was 11.2%, for the year 2010. 

It is interesting to note that as of 2006 in England, PA is not recommended as a surface course material for new or old pavements. The main reasons were the premature failures observed in some projects and its high cost. 

The service life of surface courses with PA was earlier found to be two-thirds of the service life of HRA (Nicholls 1997). 

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Porous asphalt mix specimens clogged with soil 1,300-337,600 ... 

Fwa TF, Tan SA, Guwe YK (1999) Laboratory evaluation of clogging potential of porous asphalt mixtures. Transp Res Rec 1681 43... 

Finally, improvement of the adhesion between bitumen and aggregate particles positively affects the life of surface dressings, as well as open graded and porous asphalts, and eliminates the development of ravelling. 

Mixtures to which fibres are added are the SMA and porous asphalt and occasionally in micro-surfacing. Dense asphalt mixtures with fibres were also found to have high resistance to fatigue (Samanos and Serfass 1993). The addition of plastic or iron fibres was found to increase the resistance to permanent deformation (Courard and Rigo 1993). The percentage of iron fibres added was 0.4% to 1.5%, while for the plastic fibres, it was 0.1 to 0.7%, by mass of bitumen. 

Over the last 40 years or more, new mixtures were developed in order to improve some features, such as drainage ability, noise reduction, durability and the ability to be laid in less than a 4 cm thick layer, hence economising on materials. The mixtures developed were porous asphalt (PA) in the United Kingdom, stone mastic asphalt (SMA) in Germany and AC for very thin layers (BBTM) in France. 

Asphalt concrete for very thin layers (BBTM or AC-VTL) Porous asphalt (PA)... 

The American standards basically distinguish three asphalts for road construction the AC, the open (porous) asphalt and the SMA. 

Table 5.18 Overall limits of target composition of porous asphalt...

Source Reproduced from CEN EN 13108-7. Bituminous mixtures - Arterial specifications - Part 7 Porous asphalt, Brussels CEN. 2008. With permission ( CEN). 

Material specifications — Part 7 Porous asphalt, Brussels CEN,... 

Baughan C.J., L. Chinn, G. Harris, R. Stait, and S. Phillips. 2002. Resurfacing a Motorway with Porous Asphalt Effects on Rural Noise Exposure and Community Response. TRL536. Crowthorne, UK Transport Research Laboratory. 

CEN EN 12697-17 2004-tAl. 2007. Bituminous mixtures - Test methods for hot mix asphalt - Part 17 Particle loss of porous asphalt specimen. Brussels CEN. 

Daines M.E. 1992. Trials on Porous Asphalts and Rolled Asphalt on the A38 at Burton. TRRL Supplementary Report 323. Wokingham, UK Transport Research Laboratory. 

Decoene Y. 1989. Knowledge acquired after 10 years of research on porous asphalt in Belgium. 

Morgan P.A., R.E. Stait, S. Reeves, and M. Clifton. 2007. The Feasibility of Using Twin-Layer Porous Asphalt Surfaces on England s Strategic Road Network. PPR 433. Wokingham, UK Transport Research Laboratory. 

Nicholls J.C. 1997. Review of UK Porous Asphalt Trials. TRL264. Crowthorne, UK Transport Research Laboratory. 

Phillips S.M., P.M. Nelson, and G. Abbott. 1995. Reducing the noise from motorways The acoustic performance of porous asphalt on the M4 at Cardiff. Paper to Acoustics 95. Volume 17 Part 4, Proceedings of the Institute of Acoustics. St. Albans, Hertfordshire Institute of Acoustics. 

The target bitumen content is determined by the drainage or runoff test. This is similar to the one used for hot porous asphalt (Section 5.6.1.3.4), but it is advised to use the test method proposed by the Asphalt Institute (Asphalt Institute MS-19 2008). 

The minimum rolling time depends on the type of material. The minimum rolling time for asphalt concretes and porous asphalts is 20 min, whereas the minimum rolling time for stone mastic asphalt, hot rolled asphalt and mastic asphalt is 30 min. In the case of coated chippings, the minimum rolling time is 10 min. 

For the surface layer, in particular, the asphalts most commonly used nowadays are (a) asphalt concrete for very thin layers (AC-VTL), (b) porous asphalt (PA), (c) open-graded friction course mixture (OGFC), (d) stone mastic asphalt (SMA), (e) single or double surface dressing (S-SD or D-SD) and (f) micro-surfacing (MS). Table 10.17 gives the comparative properties/characteristics for all the abovementioned surfacing materials. 

As for the top upper layer (surfacing), the recommended material is asphalt concrete for very thin layers. Other asphalts, such as porous asphalt (PA) and hot rolled asphalt (HRA) with coated chippings, may also be used in new pavements. 

If a porous asphalt (CEN EN 13108-7 2008) surface course is used over CRCB, it must be modified with a polymer or fibre additive and laid over a dense binder course. The porous asphalt should be 50 mm thick over a 90 mm binder course or 50 mm thick over a 60 mm binder course with the CRCB thickness increased by 10 mm. 

As surfacing material, the following may be considered asphalt concrete for very thin layers, porous asphalt, SMA and micro-surfacing. Details can be found in Chapter 5. Surface dressing technique may also be considered as an alternative (see Section 15.15). 

Hot asphalt surfacing overlay restores micro- and macro-texture and is the most suitable treatment for restoration of skid resistance of continuously reinforced pavement surface. All types of hot asphalts used in restoration of skid resistance of flexible pavements can be used, namely asphalt concrete for very thin layers, SMA and porous asphalt. 

In the Netherlands, the road authority for the nation s main road network, Rijkswaterstaat, has been using porous asphalt surfaces to improve the quality of their road network, in terms of both road safety and noise reduction, since 1987. Accident risk has a strong relationship with condition of a road surface. For example, in CROW (2005) it was found that the likelihood of an accident on a wet road... 

Porous asphalt appears to be an effective measure with its main benefits on traffic noise reduction (Elvik and Vaa, 2004) and better traffic performance in rainy conditions. Eurther, porous asphalt is highly appreciated by the public. However, road safety effects are very limited or non-existent due to drivers behavioural adaptation of adopting higher speeds in adverse weather conditions. Fortunately so far, no negative safety effects have become apparent and, therefore, the non-safety-related benefits prevail. Consequently, Rijkswaterstaat continues to apply porous asphalt on the main road network. 

Zwan, J.T. van der 2011. Developing porous asphalt for freeways in the Netherlands. Reducing noise, improving safety, increasing service of hfe. TR News 272, January-February 2011, 22-29. 

In a traditional resurfacing regime of Double Layer Porous Asphalt (DLPA), the top layer of the pavement is resurfaced when the quality of the road nears its failure condition. In strategy A, the resurfacing of the top layer of the heavily loaded lane is executed at 8 years after construction. 4 years later, the total DLM package is replaced, both the top and secondary layer on both the heavily and lightly loaded lanes. This is conform the current standard in asphalt maintenance. 

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