Foamed asphalt is a new cold-in-place road base recycling technology, which is offering public-works agencies new options for road-base stabilization and recycling.
The benefits of foamed asphalt-stabilized road bases are so compelling that the City of Los Angeles acquired its own road-base-recycling machine and has been using it to recycle asphalt roads.
Following an investigation into foamed asphalt technology, in late 2004 the L.A. Bureau of Street Services acquired a Wirtgen 2200 CR stabilizer/reclaimer to do foamed asphalt and other cold-in-place recycling. The city now cold-recycles failed asphalt roads in one pass, and follows with a surfacing of rubberized asphalt slurry seal.
Foamed asphalt enables contractors and state and local road agencies to undertake economical base stabilization. New foamed-asphalt technology stabilizes and improves the performance of existing road materials, producing high-quality base courses and cold mixes at the lowest possible cost.
Foamed asphalt — the product of the injection of a predetermined amount of cold water into hot penetration-grade asphalt in a series of individual expansion chambers in a base-recycling machine like the Wirtgen 2200 CR or WR 2500 S — replaces costly asphalt emulsions in 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. Unlike asphalt emulsions, foamed asphalt does not require a "break" period before it can be mixed.
And foamed asphalt technology is completely compatible with in-place recycling or crushing of degraded asphalt or gravel road wearing courses. After grading and compaction, this surface can support traffic immediately, but often is soon overlaid with a fresh, virgin wearing course. This in-situ base recycling and stabilization is the most common application of foamed asphalt throughout the world and North America.
Other benefits include:
- The recycled lift is more resistant to penetration of water.
- Foamed asphalt-stabilized bases are usually less expensive than a bituminous emulsion or a combination of emulsion and cement.
- Additional water is not added to the recycled material, as is necessary when emulsion is used.
- The rapid strength gain from use of foamed emulsion means that traffic may be introduced onto the recycled road as soon as compaction is complete.