Hot-in-place Recycling Key to Denver's Street Maintenance

The rejuvenated pavement is then reapplied and distributed with a screed as a 1-inch leveling course. While remaining at a minimum 225 degree F, a virgin hot mix asphalt mat is placed over the recycled leveling course. Heating, scarifying, applying rejuvenating agent and applying new overlay is done in a one-pass process with the proprietary equipment Cutler uses. The process not only improves bonding between the recycled leveling course and the new driving surface, but it also reduces the construction traffic in and out of a work zone since both aspects of the process are completed simultaneously.

For Roberts and Denver taxpayers, the process delivers a high-quality road with fewer disruptions to homeowners and motorists, and at a cost that's lower than conventional mill and overlay roads.

The efficiency of heating up a road surface to rework the aged material and then using that same heat to bond a new driving surface results in a better engineered structure that will not delaminate because the two layers (recycled leveling course and new HMA driving course) have been compacted into one lift. And additional engineering benefit to the hot in-place process is that all joints and seams are also thermally bonded. When paving and adjacent lane, the recycling train reheats the edge of the completed repaved lane, resulting in a more durable, higher-density seam when compacted together.

Chip seal — the other preservation component

To further extend the life cycle of its streets, Denver also uses a chip seal program to preserve recently paved roads. Chip seal is the first surface treatment applied approximately seven years after a new or mill and overlay road has been constructed. In 2006, over $1 million has been earmarked for the street maintenance division's chip seal program.

Through its street management analysis program, chip seal extends the life of the asphalt another seven years before the road becomes a candidate for the hot in-place process. As a result, the hot in-place strategy is an intermediate maintenance step between chip seal preservation and a full rehabilitation mill and overlay project. That allows the city and county of Denver to get about 20 years out of an average road, generating a substantial reduction in its overall pavement management costs.

"On average, hot in-place has reduced our pavement management costs by 20 percent," Roberts notes. "When you combined that savings with what we're doing with chip seal, you can see how we're maximizing the dollars we spend on building and maintaining good roads. Even with some of the budget cuts we've experienced recently, we're still able to operate a substantial resurfacing program to keep our roads in good condition."