California motorists and taxpayers were big winners when the cutting-edge cold-in-place (CIP) pavement recycling was used to rehabilitate a major portion of busy I-80 from Auburn to Colfax, north of Sacramento.
The California Department of Transportation (Caltrans), Teichert Construction and Valentine Surfacing — with the participation of Wirtgen America Inc. — reconstructed I-80 this past summer using the unique CIP foamed asphalt recycling process. A massive 1,280-hp Wirtgen WR 4200 milled up the existing pavement, mixed it with asphalt foam, then mixed it with a cement-water slurry from an accompanying Wirtgen WM 1000. This new innovative material was placed and compacted on the roadway, all in one pass.
The recycling process resulted in direct savings to California taxpayers of well over $1 million compared to conventional reconstruction.
This project combined the asphalt reclaiming and foamed mix capabilities of the WR 4200 with the cement slurry capabilities of the WM 1000 to recycle in-place nearly 27 miles of traffic lanes (approximately 188,950 square yards), and nearly 49 miles of shoulders, (approximately 315,525 square yards). It represents the first use of the WR 4200 in the United States and one of the largest such projects in the world to date.
“We thought it was a great success,” says Larry Rhoden, vice president and manager, Teichert Construction’s Heavy & Highway Division. “More importantly, because it was Caltrans, it’s really encouraging for the recycling industry as a whole. It’s really the tip of the iceberg of what can be done. It’s the future, without a doubt.
“There are so many reasons for recycling,” Rhoden continues. “Raw resources are becoming very constrained; it’s getting harder and harder to permit new aggregate extraction sites. With the price of oil being what it is, recycling just makes sense using this method.”
The quality and the environmental aspects of the project were such that the project was entered into the annual Globe Awards program of the American Road & Transportation Builders Association, which recognizes a project’s contribution to environmental protection and impact mitigation.
“The I-80 project was extremely challenging, an application that had never been attempted before on an Interstate highway,” says Wirtgen recycling specialist Mike Marshall.
Foamed asphalt and I-80
Foamed asphalt is a cost-effective way of stabilizing road bases that’s gaining interest from coast-to-coast. Foamed or “expanded” asphalt is created by carefully injecting a predetermined amount of water into hot penetration-grade asphalt in the mixing chamber of a pavement remixing unit, and offers a cost-effective alternate for road base stabilization.
The expanded asphalt has a resulting high surface area available for bonding with the aggregate, leading to a stable road base using 100 percent of the existing in-place materials. The benefit is substantial cost savings over use of asphalt emulsions for base stabilization, and complete elimination of the cure or “break” period.
On I-80, the foamed material was paver-laid, with an integral Vögele high-density, variable-width screed and compacted, and could accept traffic — including heavy trucks — almost immediately.
Foamed asphalt is produced by adding small amounts of water (approximately 2 to 3 percent by mass of asphalt) to hot liquid asphalt, typically 320 to 350 degrees F. The liquid asphalt used for the process can be straight penetration grade; in the I-80 project, it was PG 64-22.
When injected into the hot liquid asphalt, the water evaporates abruptly, thus causing extremely rapid expansion of the liquid asphalt in the saturated steam. Typically the liquid asphalt expands 15 to 20 times its original volume. The intensity and effectiveness of the foaming process can most effectively be governed by controlled operation of the basic physical conditions, such as pressure and temperature.