Pavement Structural Analysis Introduction Part 3 Pavement Types

Pavement Structural Analysis Introduction (Part 3) Pavement Types, Flexible Pavement Highway and Transportation Engineering Al-Mustansiriyah University 2020 -2021 Dr. Rana Amir Yousif & Dr. Abeer K. Jameel

Flexible Pavement Full - depth asphalt pavements: � constructed by placing one or more layers of Hot Mix Asphalt (HMA) directly on the subgrade or improved subgrade. � This concept was conceived by the Asphalt Institute in 1960 � It is generally considered the most cost-effective � dependable type of asphalt pavement for heavy traffic. � This type of construction is quite popular in areas where local materials are not available. � It is more convenient to purchase only one material, i. e. , HMA, rather than several materials from different sources, � thus minimizing the administration and equipment costs.

Flexible Pavement According to the Asphalt Institute (AI, 1987), full-depth asphalt pavements have the following advantages: � They have no permeable granular layers to entrap water and impair performance. � Time required for construction is reduced. � On widening projects, where adjacent traffic flow must usually be maintained, full-depth asphalt can be especially advantageous. � When placed in a thick lift of 4 in. (102 mm) or more, construction seasons may be extended. � They provide and retain uniformity in the pavement structure. � They are less affected by moisture or frost. According to limited studies, moisture contents do not build up in subgrades under full-depth asphalt pavement structures as they do under pavements with granular bases. Thus, there is little or no reduction in subgrade strength.

Flexible Pavement Typical layers of a flexible pavement Seal Coat: Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance where the aggregate in the surface course could be polished by traffic and become slippery.

Flexible Pavement Tack Coat: �Tack coat is a very light application of asphalt, �usually asphalt emulsion diluted with water. �It provides proper bonding between two layers of binder course �must be thin, �uniformly cover the entire surface, and set very fast. �It does not require penetrating into the underlying course.

Flexible Pavement Prime Coat: �Prime coat is an application of low viscous cutback bitumen to an absorbent surface like granular bases which binder layer is placed. � It provides bonding between two layers. �Unlike tack coat, prime coat penetrates into the layer below, plugs the voids, and forms a water tight surface.

Flexible Pavement Surface course: � It is the layer directly in contact with traffic loads � generally contains superior quality materials. � They are usually constructed with dense graded asphalt concrete (AC). � It provides characteristics such as friction and smoothness. It must be tough to resist the distortion under traffic and provide a must smooth skidresistant riding � It be and water proof to protect thesurface, entire base and sub-grade from the weakening effect of water. It will prevent the entrance of excessive quantities of surface water into the underlying base, sub-base and subgrade,

Flexible Pavement Surface course:

Flexible Pavement Binder course � This layer provides the bulk of the asphalt concrete structure. � Its chief purpose is to distribute load to the base course � the binder course generally consists of aggregates having less asphalt and doesn't require quality as high as the surface course, � so replacing a part of the surface course by the binder course results in more economical design.

Flexible Pavement