Hollywood stabilized by a bitumen film.

The road which leads to the most famous letters in the world, the Hollywood emblem on the slopes of Mount Lee, had become brittle over time. The serpentine road leading to the top of the mountain is mostly used by supply and security vehicles. The asphalt pavement showed widespread alligator cracking. Poor rainwater drainage had additionally taken a heavy toll on the pavement structure. The City of Los Angeles believed that cold recycling was the most suitable method of repair, as it offered significant cost benefits. Conventional rehabilitation by transporting the old pavement away and supplying new mix would have posed too much of a problem because of a residential area with narrow streets located in the neighbourhood of the job site.

Applying the “in-situ” cold recycling method, a Wirtgen cold recycler type WR 2500 recycled the upper pavement structure to a depth of 150 mm. The milled material consisted of gravel and asphalt in equal proportions and was homogeneously mixed with 3% of foamed bitumen in the recycler’s variable mixing chamber. Equipped with a powerful 610 HP engine, the WR 2500 had no problem pushing the bitumen tanker truck uphill through the serpentine bends. The ideal composition of the foamed bitumen had previously been determined by means of a Wirtgen foamed bitumen laboratory plant WLB 10.

Compaction of the recycled pavement posed a great challenge on the steep hillside, so that different types of Hamm rollers followed right behind the cold recycling train. A single-drum compactor 3412 worked immediately behind the WR 2500, followed by a motor grader cutting the final shape, and a double vibratory roller HD 120 which ensured the final density of the recycled road pavement. A pneumatic tyred roller GRW 18 completed the operation by sealing the new surface.

The resulting pavement structure is much more flexible and will improve the road’s bearing capacity in the long term, preventing renewed cracking.

Job site: Slopes of Mount Lee, Hollywood