August 21st, 2012
BETTER JOINTSPreserve Infrastructure, by Catherine Higgins.
Better longitudinal joints in asphalt pavement mean longer pavement life.
A longitudinal joint in Hot Mix Asphalt pavement is formed when a new batch of asphalt is placed adjacent to existing pavement. Because of temperature and plasticity differences, sometimes the newer and older pavements fail to bond, and the joint has significantly less density than the rest of the pavement.
A long joint that is not compacted adequately can be “the weak link in the pavement,” explains Kevin VanFrank, UDOT Engineer for Asphalt Materials. “What you have is a seam in the mat that’s difficult to keep water out of.” Because the joint is permeable, water seeps in, the pavement ravels and loses material. Soon that damage “starts to migrate into the balance of the system…you can lose the entire pavement system.”
Under the best of circumstances, joint is typically less compacted than the mat. Van Frank says that a small difference of two to three percent can be acceptable.
HMA mix designs also play a role in the compaction at the joint. “As we attack rutting, we end up with mats that are more difficult to compact and lose the compaction in the joints without making special effort.”
The best solution to achieving good compaction at the long joint is to use echelon pavement placement and install two widths of pavement at the same time. UDOT’s specification states that echelon paving is preferred; however, the method is not always practical because lane closures are required. When echelon paving is not practical, other techniques should be employed.
A survey of each of the fifty states conducted by the Federal Highway Association shows that long joint health is a big concern among departments of transportation. Half of the states were found to be not satisfied with the overall performance of long joints, however, not all states have specifications in place that seek to achieve good compaction.
Some states had density specifications in place and others defined accepted construction techniques. But, even though the survey found an array of best practices being employed, a definitive solution was not identified.
In an effort to find the best solution to achieve good joint compaction, UDOT will select projects and look to the paving industry to identify good construction techniques. “Our intention is to implement the compaction of the long joint to a standard value.”
“We’re going to define an outcome and let industry meet the outcome,” says VanFrank. “We have seen techniques used this year that make joint density approach mat density.” Van Frank believes that by using UDOT will select appropriate projects to be built next year and allow contractors to lead the way UDOT will be able to identify the best solutions to ensuring better joints.