Abstract:
107252-1.pdf Often the natural ground or soil is not mechanically strong enough to withstand the repeated applications of wheel loads without significant deformation. Therefore it is necessary to provide a structure between the wheel and natural ground or subgrade to spread the wheel loads within allowable and recoverable deformation limits. Road pavement is the structure, which serves this purpose, by supporting and distributing the applied load. The primary purposes of the pavement are to prevent excessive deformation of the subgrade and to prevent ultimate failure stage. In order to prevent excessive subgrade deformation the vertical stress oz at subgrade level has to be kept below some critical value. The two main types of pavements used in pavement construction are rigid pavements and flexible pavements. Rigid pavements are very rare in Sri Lanka and consists of very stiff reinforced or roller compacted concrete surfacing over comparatively much softer ground. Flexible pavements consist of three main layers from top to bottom, consisting of the bituminous surfacing, road base and sub base. Sometimes the subbase is not laid. The shear strength, stiffness and the quality of the material of the layers decrease in the downward direction of the pavement. The topmost layer of a flexible pavement is an asphalt concrete surfacing or any other bituminous surface dressing like Double Bituminous Surface Treatment (DBST), Single Bituminous Surface Treatment (SBST) or traditional metal and tar application. The most popular bituminous surface treatment in Sri Lanka is asphalt concrete due to its very good riding quality, durability, higher stiffness or stability, resistance to adverse climatic conditions and the ability to maintain consistent quality during manufacturing and laying. As asphalt concrete surfacing is the most modern and popular method used in flexible pavement construction, this work is limited to studies on flexible pavements with asphalt concrete surfacing. Primarily asphalt concrete is a mix of bitumen and a blend of densely graded aggregates. Mix proportions of the asphalt concrete are determined after a process of mix design to achieve the desired strength and durability against expected traffic and adverse climatic conditions by using available aggregate.
