Project: I-65 Double-lift paving - Nashville, TN
Contractor: APAC - Memphis, TN
Project obstacles and solutions: In an effort to increase highway safety and control costs, the Tennessee Department of Transportation specified that sections of I-65 through Nashville, Tennessee would be finished with concrete pavement using an anti-skid stone in the mix. They also developed a plan to use a double-lift paving process. This was the first time this method of paving had been tried on a highly traveled interstate highway.
Anti-skid stones are highly polished aggregates that are used as the coarse raw materials in a paving mix. The concrete is finished to produce a high speed friction surface. The pavement on I-65 required 12 inches of concrete. APAC paved the bottom 8 inches using a normal coarse aggregate mix. This was covered by an additional 4 inches of anti-skid concrete pavement. To ensure that the two layers bonded, timing and mix design were critical. IMI delivered a low-slump, high-density concrete for the base layer via tri-axle dump trucks. This helped speed up the paving process. The dump trucks unloaded the concrete on the ground ahead of the first of two slip-form pavers. A second paver followed behind the first. It finished the paving process with the anti-skid mix, delivered via mixer truck. This mix had a 2-3 inch slump range. APAC then dragged a burlap fabric over the finished surface to enhance friction.
The challenge of this project was making sure the concrete of the first lift was bonding properly to the top lift. IMI mixer trucks were dispatched to get to the job site immediately after the dump trucks had unloaded and the first paver was moving. APAC used a vibrator in the second paver to bond the two surfaces together. Each mix was tested on the site. IMI dispatch, drivers, QC/QA, sales representatives and plant operations personnel worked together to make sure concrete was being delivered to the project at the right pace.
The double-lift method is being studied by several states and the U.S. Department of Transportation.