If a joint is unconfined (either at the roadway edge or as the first lane placed) roller passes over the joint will cause it to deform sideways rather than compact. The joint deforms rather than compacts.Because it has been moved more and moved beyond the end of the auger, this material has a higher likelihood of being segregated. Because longitudinal joints occur at the edge of the paver screed and auger system their constituent material can come from material pushed out beyond the end of the auger and/or screed.
The joint contains segregated material.Longitudinal joints often look coarse, open-graded or segregated (Figure 4).
Surface Irregularities Figure 4: Surface irregularities. Lower densities at unconfined shoulder edges are also generally acceptable because even if they are porous enough to allow water infiltration, they are not subject to much loading and they are usually sloped towards the shoulder, which allows an infiltrating water to quickly drain away (Brock and Skinner, n.d. Longitudinal joint densities that are slightly less than the mat average (on the order of 1 – 2 percent) are generally acceptable because, if properly placed, longitudinal joints with these densities (usually about 91 or 92 percent of Theoretical Maximum Density) are usually not subject to much loading, and their air void content is not high enough to cause significant raveling. Many agencies that specify minimum densities (maximum air void contents) for HMA construction specifically exclude joint areas because of this. Furthermore, the overall joint does not typically meet minimum density requirements established for the mat as a whole. Typically, the hot side of the joint is about 2 – 4 more dense than the cold side (Kandhal and Mallick, 1996 ). The subsequent lane (hot lane) is confined by the cold lane and therefore tends to be more dense. As the roller passes over, this unconfined edge tends to deform laterally rather than compact. Low joint density is common since the edge of the lane first paved (cold lane) is unconfined. Usually a well-constructed joint will be about 1 – 2 percent less dense than the rest of the lane away from the joint, however a poorly constructed joint can have significantly lower density – on the order of 5 – 10 percent (Kandhal and Mallick, 1996 ). Keep in mind that “low density” and “high air voids” refer to the same thing]. Low density is general HMA problem that can lead to numerous distresses including decreased stiffness, reduced fatigue life, accelerated aging/decreased durability, rutting, raveling, and moisture damage (Hughes, 1984 Hughes, 1989 ). If no construction precautions are taken, the longitudinal joint of a multi-lane paving project will often be significantly less dense than the majority of the pavement and contain surface irregularities that may or may not be caused by segregation. As a newly placed mat is compacted, its thickness decreases and it becomes more dense. The material beyond the anticipated final mat thickness. This area is typically at the outer edge of the cold lane taper in the joint overlap area and can have densities. That portion of the cold lane that is at a significantly lower density than the rest of the cold lane. The width that the hot lane overlaps the cold lane. Mix temperature is at or near ambient temperature and the lane can support traffic loads. This section uses the following terms when referring to longitudinal joints (see Figure 3): 02-03.įigure 1: Longitudinal joint showing good performance (no cracks or raveling).įigure 2: Longitudinal joint showing poor performance (notice the jagged crack). Evaluation of Eight Longitudinal Joint Construction Techniques for Asphalt Pavements in Pennsylvania. Longitudinal Joint Construction Techniques for Asphalt Pavements. A Study of Longitudinal Joint Construction Techniques in HMA Pavements (Interim Report – Colorado Project). This section is taken largely from three National Center for Asphalt Technology (NCAT) reports: These distresses, caused by relatively low density (high air voids) and surface irregularity at the joints, can largely be avoided through proper construction techniques and equipment. Improperly constructed longitudinal joints can cause premature deterioration of multilane HMA pavements in the form of cracking and raveling (Figures 1 and 2). A longitudinal joint is the interface between two adjacent and parallel HMA mats.