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What are the different functions of aggregates, filler and binder in bituminous pavement?

In bituminous materials, course aggregates perform the bulking action of the mixture and contributes to the stability of resulting mix. Fine aggregates form the major proportion of mortar.
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What is the purpose of tar in bituminous materials?

Tar is commonly incorporated in bituminous materials because of the following reasons:

(i) Blending of tar with bitumen possesses better binding performance with roadstone than bitumen. Continue Reading »

Why do some countries have reservation on the use of friction course as bituminous surface layers?

Owing to the porous nature of friction course, its deterioration rate is faster than conventional bituminous materials and the durability of friction course is a main concern form users. The service life of friction course is reported to be around 8-10 years.
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What is the importance of friction course to expressways and high speed roads?

Friction course, which is known as porous asphalt, is often used as surface material in high speed roads and expressway. It is porous in nature which allows for speedy drainage of surface water. Road safety can be improved because it reduces the chance of hydroplaning/aquaplaning (i.e. there is a layer of water between the tires of the vehicle and the road surface. It may lead to the loss of traction and thus prevent the vehicle from responding to control inputs such as steering, braking or accelerating). It also decreases the splash and spray from vehicles in wet weather. It serves as a drainage channel for water to flow beneath the pavement surface.
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What are “mortar mechanism” and “stone contact mechanism” in bituminous materials?

“Stone contact mechanism” applies to well graded aggregates coated with bitumen (e.g. dense bitumen macadam) where the traffic loads on bituminous roads are resisted by stone-to-stone contact and by interlocking and frictional forces between the aggregates. It is essential to adopt aggregates with a high crushing strength. The bitumen coatings on the surface of aggregates merely serve to cement the aggregates together.
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