Low longitudinal joint density has been identified as one of the major issues relating to poor asphalt pavement performance. Low longitudinal joint density can lead to premature raveling of the joint and the lower density results in increased permeability of the pavement. Increased permeability allows water to easily enter the pavement resulting in increased susceptibility to moisture induced damage or stripping.
Rather than specify a method of longitudinal joint construction, most owner agencies prefer to specify a final product and let the contractor determine the methods and/or equipment. However, due to the steep density gradient that exists at longitudinal joints it is recommended that DOTs spell out exactly where and how to test joint density.
Pavement cores have traditionally been used to evaluate pavement density or compaction. Nuclear and non nuclear gauges have been utilized as well but both require correlation to densities obtained from cores. The reported drawback to using gauges to measure longitudinal joint density is the inability of the gauge to seat firmly on the joint, making it impossible to get an accurate reading directly at the joint. Cores can directly measure joint density; however, density results are not immediately available and patching of the hole is required which can lead to water infiltration.
Field permeameters have recently been developed that can readily measure HMA permeability. If a correlation can be obtained between longitudinal joint density and field permeability then a simple direct method would be available to control longitudinal joint permeability and indirectly control longitudinal joint density.