NOISELESS PAVEMENTS

INTRODUCTION:

  • Transportation related noise is not merely an annoyance; like other forms of pollution, it has wide-ranging adverse health, social, and economic effects.
  • Globally, highway traffic noise is a growing problem, particularly, in urban areas where traffic is growing at a rapid pace, and is seriously considered a sustainable "quality of life" issue.
  • 3 decibel noise addition is estimated with each doubling of traffic. 

SOURCES:

  • Propulsion/engine noise
  • Aerodynamics
  • Road/Tyre interaction

Vehicles travelling at speeds greater than 40 km/hr , road-tyre interaction becomes a dominant source of noise pollution in highways (accounts to about 75-90% of the overall highway noise energy).

Road tyre noise

Depends upon various factors, 

  • Air is compressed, squeezed out and sucked back in through successive impacts between the tyre grooves and the road surfaces.
  • Pavement's texture and its bulk properties are major governing factors. Generally, pavement mix designs are done keeping in mind its texture, porosity, stiffness, voids, number and thickness of layers.

Porosity: Higher the porosity, lower the noise as it reduces the pumping of air through the tyres.

Voids: Noise fails to propagate properly as the voids filled with air have a dampening effect on the propagating acoustic wave. Therefore its size and number plays an important role. Smaller the voids and increase in its number decreases the noise level significantly

Thickness: Generally thicker the pavement, lesser is the noise.

Pavement age: Every one year 0.5dB increase in the noise level.

Vehicle speed: Increase in speed increases the pumping of air, thereafter increases the noise level.

Noise optimised pavement technologies:

POROUS ASPHALT

  • Porous asphalt (PA) is to date, the most efficient road surface technology in terms of noise reduction. It is mostly used as a single porous layer.
  • 15-30% air voids.
  • Thickness ranging from 40mm to 50 mm is generally seen.
  • Clogging of porous asphalt is a main concern; as it reduces its efficiency. Therefore is used in high volume high speed roads where the suctioning effects of tyres on pavement tend to pull out debris from the pores.

POROELASTIC ROAD SURFACE (PERS)


  • PERS is defined as a mix that contains from 20 to 40% of air voids and is mainly made of rubber. The rubber content is about 20% in volume of the mix. Aggregates and rubber are bound by a polymer modified asphalt or polyurethane binder.
  • Virtually, any type of good performance binder could be used; however, only bitumen and polyurethane binders have been used to the present time.
  • This type of material provides a very elastic surface which is beneficial to the vibration rolling noise produced by vehicle According to Swedish-Japanese studies, poroelastic road surface provides an effective reduction of tyre-pavement noise between 5 and 15 dBA compared with conventional dense asphalt surfaces.
  • Not used extensively as it fails to provide sufficient adhesion between the pavement and the base course. Low skid resistance and poor fireproof performance contributes as well.
  • Relatively new technology and is expensive.

STONE MASTIC ASPHALT (SMA)

  • Small size aggregates are generally used (5mm or 6mm).
  • Gap graded course concrete.
  • Fibres are used in the mix along with powdered crumbs of rubber.
  • Void content ranges from 5 to 10%

ASPHALT RUBBER FRICTION COURSE (ARFC)

  • An asphalt rubber friction course (ARFC) is usually a wearing surface layer that is built using either a gap graded or open- graded asphalt mix and which contains from 15 to 20 percent of crumbs of rubber in it, by weight of liquid asphalt cement.
  • Noise reductions range up to 6.7 dBA.
  • Costly

THIN, VERY THIN AND ULTRA-THIN SURFACING (VTAC)

  • Laying down is easy and quick, thus limiting traffic hindrance and costs.
  • Surface properties are homogeneous and can be good in terms of noise reduction and often excellent in terms of skid resistance.
  • Open-graded thin layer are becoming very popular for noise reduction in urban areas, where porous surface are banned because of clogging problems and low shear resistance.
  • The use of modified bitumen with polymers prevents the binder from flowing and enhances the mechanical properties and the durability of the mix.

Reductions of road traffic noise between 3 and 9 dB

CEMENT CONCRETE SURFACES

  • Porous concrete is the only type that can be considered as "quiet". The void content is large, intentionally built in by using a gap- or open-graded mix.
  • Porous asphalt concrete, porous cement concrete provides both low noise emission and good drainage capacity.

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