Longitudinal joint densities are typically compared to mat densities as:

Longitudinal joint densities are typically observed to be lower compared to mat densities due to several factors related to the construction and placement of hot mix asphalt. When asphalt is laid down, the mat density reflects the overall compactness of the asphalt layer across a larger area. However, longitudinal joints, where two passes of asphalt meet, often experience challenges that can lead to reduced density.

These challenges might include insufficient compaction at the joint due to the difficulties in maintaining adequate pressure and coverage at these critical interfaces, potential variability in temperature, or inconsistencies in material application. As a result, the longitudinal joint may not achieve the same density as the surrounding mat, leading to a lower density measurement.

Understanding this distinction is crucial for inspectors, as it directly impacts the overall performance, durability, and longevity of the pavement. Lower density at the longitudinal joint can result in increased susceptibility to moisture ingress, raveling, and potential structural weaknesses over time. This knowledge helps inform decisions regarding quality control and the necessity for corrective actions during construction processes.