A residential street that intersects the famed Melrose Avenue in the heart of the Fairfax and Hollywood District of Los Angeles, Ogden Drive, is a typical street built in the 1940s and ’50s. Its thin lift of hot-mix asphalt over a silty sand subgrade was adequate then, but in the heart of modern-day Hollywood, the road is not winning any Oscars. The city of Los Angeles Bureau of Street Services was charged with finding a cost-effective urban street reconstruction process.
The solution for this innovative agency was found when the city went to Palm Springs to see a solvent-free cold in-place recycling Reflex project on Highway 111, a project that produced good coating and an engineered approach to mix design. But the city still had reservations because it felt the recycling train was too large for an urban environment and that a majority of the streets did not have an existing asphalt section thick enough to support the recycle train. Within two years, the city solved part of its problems by purchasing a Wirtgen 2200 recycling machine—smaller and more compact. In October 2005, the city set up a test section with SemMaterials L.P. to try the Fortress process using asphalt emulsion on Ogden Drive, just two miles from the famed Paramount Studios.
Fortress is a process for full-depth reclamation that consists of an engineered mix design, performance-related specifications and an innovative asphalt emulsion to produce a flexible bituminous stabilized base that is strong enough for traffic before surfacing and improves cracking resistance and moisture susceptibility.
On the Ogden Drive test section, the city needed a process that could be utilized for both full-depth reclamation and cold in-place recycling. The test section consisted of two city blocks and was 30 ft wide. The recycling depth was 4 in., while the road structure was 21?2 in. of cracked, aged pavement that, according to some residents, had received only minimal maintenance over the last 40 years. Intersections were at least 4 in. of asphalt.
For Ogden Drive, the city used its Wirtgen 2200 recycler, with the built-in tamping bar screed—the only machine of its type in the U.S. The recycling machine was followed by two Hamm rollers, allowing the 30-ft-wide project to be reclaimed curb to curb with the elimination of some typical equipment. For the cold in-place recycling streets, the pug mill crushing unit and paving machine were eliminated; for the full-depth reclamation, a padfoot roller and motor grader were eliminated.
After the pulverizing and mixing of the Fortress mix was complete, traffic returned only two hours later. A 2-in. hot-mix overlay was applied five days later. The residents were thrilled they had access to their homes throughout the entire construction process.
One of the leading innovative agencies in the nation, the city of Los Angeles, along with SemMaterials, expects that other agencies will see the impressive results of the Ogden Drive project and also will venture “out of the box” to strike gold.
