The business of today's paving contractor is growing more difficult with each passing season. Seemingly being squeezed from all sides — longer hauling distances from the plant to the jobsite, complex mix designs using coarse aggregates prone to segregation and more stringent performance-based specs — contractors find it necessary to arm themselves with the latest technologies available in order to stay in business.
Although portable plants make it somewhat easier for contractors to obtain permits, finding a site for these plants can be difficult, especially in densely populated areas. The "not-in-my-backyard" attitude has pushed asphalt plants further away from paving jobs, with transport times of an hour or longer being the norm. This distance not only requires higher asphalt mix temperatures leaving the plant, but it also forces the paving crew to deal with thermally segregated material.
The growing popularity of performance-based specs calling for stone matrix asphalt (SMA) and Superpave mixes for highway, interstate and airport applications put more pressure on contractors to deliver a high quality mat that lasts. These tighter specs are a double-edged sword with the larger, coarser aggregate delivering more durable roads but are also more prone to segregate. Even by following proper paving techniques, unless contractors deal with particle segregation road service life will be shorter and more costly to maintain.
Feel the heat
Whereas material segregation is easily detectible by the naked eye, highway and airport paving contractors are employing techniques to identify the invisible form of segregation. Thermally-segregate material in the delivery truck results in uneven mat temperatures left behind traditional slat conveyor pavers, which make compaction more difficult.
With today's stricter tolerances of many state performance-based specs, there is a narrow window of opportunity for the rollers in the paving train. "There is about a 40-degree window for each roller to compact the mat to optimum densities," says Stuart Culver, project manager for Holmes & Murphy, an Orchard Park, NY-based paving contractor. If temperatures vary significantly across the mat, it's more difficult for the roller to compact at the right temperatures in order to reach spec densities.
Longer hauling distances greatly increase the chances for material at the top and sides of the truck to cool. In some cases, material at the core can be in excess of 50 degrees warmer than material at the outer edges of the delivery truck. Without some means of reblending the asphalt, meeting spec densities is nearly impossible.
This is a primary reason why paving contractors like Dublin, CA-based DeSilva Gates Construction utilize equipment like the Terex/Cedarapids Remix pavers from Terex Roadbuilding on tough performance-based contracts. Pavers with the Remix Anti-Segregation System are designed specifically to address both material and thermal segregation issues.
Two sets of twin counter-rotating augers in a Remix paver's hopper replace the traditional slat conveyor delivery system. Whereas slat conveyor systems pull material from the front of the hopper back, the reblending augers pull uniformly from all areas of the hopper and spread material over an area five times larger behind the screed. This reblending action virtually eliminates both material and thermal segregation, allowing the rollers to more easily compact the mat to spec densities.
CA long haul
DeSilva Gates recently used its 562 Remix paver on a seven-mile stretch of Highway 70 north of Sacramento. The job required approximately 100,000 tons of asphalt, which consisted of five inches of a 1.5-inch base mix, then two inches of a ¾-inch aggregate mix and finally a one-inch, open-graded top course for water dissipation and improved traction. The mix was laid in windrows and transferred to the paver's hopper by a Terex/Cedarapids MS2 Pick-Up Machine.