General Knowledge
Xavier Guyot
Colas Asia – Pacific
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The rapid development of the world economy and especially in ASIA region during the last two decades has generated a strong growth of heavy traffic on main road networks and by consequence requires a high level of maintenance of existing roads or new road building. This heavy traffic constituted of single, double or even triple wheel axles trucks influence the durability and the long term performances of pavement making roads structure more vulnerable to deformation.
The direct consequences of this increasing aggressiveness result in deep and fast structural deterioration of road structures that are characterized by two main distress modes: the permanent deformation (also called rutting) and cracking by fatigue.
Causes are well-known:
•    Pavement design method: Lack of reliable data of traffic and axle load in addition with inappropriate design methodology can result in underestimated thickness of asphalt layers.
•    Outdated asphalt pavement specifications: So far they are based on volumetric method (Marshall) and not on mechanical performances (Stiffness Modulus, resistance to rutting and to fatigue)
•    Inappropriate bitumen choice: In many countries, the common practice still consists in using soft grade pure bitumen which is inappropriate to withstand severe constrains of traffic and high service temperature.

Performances of binder play a key role in the performances of the asphalt pavement as the properties of both are linked. Using Polymer Modified Bitumen can improve considerably the pavement performances for wearing course and binder course regarding the Rutting resistance and thermal susceptibility.
Using in pavement structure base course Asphalt Concrete manufactured with Hard Grade bitumen like “High Modulus Asphalt” or French “Enrobé à Module Elevé” with improved mechanical characteristics can lead to pavement reduction thickness or longer service life, by preserving resources and bringing cost savings.
Combination of this both type of “High Performances Asphalt”, PMB for surface course and Hard Grade for base course, with the strong extension of service life and increase of traffic being supported, make these specific materials economical by reducing significantly the frequency of maintenance and the thickness of asphalt layers.
This paper focusses on the presentation of characteristics and performances of asphalt materials using specific type of bitumen and their impact on asphalt pavements durability illustrated by some case studies.