Comparison of Flexible Pavement Geotechnical Parameters in Highways Technical Specifications

Flexible pavements, also called asphalt pavements, are constituted of a bituminous surface course, subbase, and base layer constructed over a subgrade. The bituminous surface layer consisting of one or two layers transfers the traffic loads to the lower layers. The subbase and base layers of flexible pavements are constructed to support the surface layers and to distribute the loads from these layers to the subgrade safely. These layers must have the sufficient bearing capacity to support the surface layers and should also be resistant to detrimental environmental effects. In addition, the thickness of pavements is directly dependent on the bearing capacity of the subgrade. The materials used for the construction of the subgrade, subbase, and base layers in Turkey must meet the requirements specified in the Turkish Highways Technical Specifications. The previous specification published in 2006 was replaced by a new specification in 2013, which is still in effect. The current study compares the geotechnical parameters of the Highways Technical Specification published in 2006 and 2013 with a particular focus on flexible pavements. For an appropriate flexible pavement design, the importance of using high-quality and rigid materials that are more resistant to heavy loads, fragmentation, water sensitivity, and wearing effects of freezing and thawing is highlighted.