Question

Compare between Flexible Pavement Design using Asphalt Institute Methods and AASHTO Design method.

Answer 1

Flexible payment structures are made up of different layers of different categories of materials and all pavement structure deflects when the load is applied or on application of load that is why these are named Flexible pavement.Each and every layers of these structures receives load from different layers amd passes to the different one.

Comparison between the Asphalt Institute Method and Aastho design method

Asphalt Institute Method

It is based on the two different assumption of strain-stress conditions

The wheel load is transferred to surface through tire by uniform vertical pressure.The stress then developed by spreading over the structure to minimise vertical pressure.

Wheel load causes both compressive and tensile stress in pavement structure.

The horizontal tensile strain is maximum on bottom.of Asphalt layer in this method.

And Vertical compressive strain is on subgrade too which results in deformation permanently.

Thicker the Asphalt layer and granular load at these two point minimum strain will develop under the traffic loads

The Asphalt Institute method follow mechanism as emerical anaylis method.

It is necessary that large taffic and the load occuring through it requires thicker pavement.

Tha Aastho design method is based on empirical method .The design were first developed on the basis of the research done on the damage occurred on the test loops of the Aasho Road test which was conducted in Ottwa.

The method is based on the limitation of overall fatigue and rutting damages.

Aastho method also includes environmental and material factors such as moisture, drainage and soil conditions for its design considerations.

Design of both the methods based on

Local roads and resedential

Collector roads

Aerial stress and industrial drives

Aashto method is used to design new Highway pavement design.

Maximum use of this design is done .