Showing good form in Los Angeles

April 22, 2010

When paving a new 4,000-ft concrete bike and pedestrian path, the city of Los Angeles reduced both time and costs by using reusable metal forms that were easy to set and a truss screed that simplified finishing.

The city recently completed the path, which links an existing bike path in Burbank to the NOHO (North Hollywood) arts district. It is a 98% compacted, 4-in.-thick crushed aggregate base (CAB). A 6-6-10-10 wire mesh reinforcement was pulled up halfway through the thickness of the concrete with hooks during the paving process.

When paving a new 4,000-ft concrete bike and pedestrian path, the city of Los Angeles reduced both time and costs by using reusable metal forms that were easy to set and a truss screed that simplified finishing.

The city recently completed the path, which links an existing bike path in Burbank to the NOHO (North Hollywood) arts district. It is a 98% compacted, 4-in.-thick crushed aggregate base (CAB). A 6-6-10-10 wire mesh reinforcement was pulled up halfway through the thickness of the concrete with hooks during the paving process.

Instead of wood forms, which can be used a limited number of times and are difficult to clean, the city chose Base Line heavy-duty forms from Metal Forms Corp. of Milwaukee, Wis. These 10-gauge steel forms are easy to set up and are designed to provide long service life. They incorporate box-type stake pockets with wedges, which eliminate nailing and allow quick vertical positioning of the forms without the need to pull nails. They also feature full-height end connections that make it easy to connect the 10-ft form sections and provide full-depth alignment with a sturdy reinforced joint.

A vibrating truss screed was used to strike-off, consolidate and finish the concrete. It included a 5 ½-ft power section with 10- and 2 ½-ft extensions, plus a hydraulic winch and a back-up hand winch. It also incorporates square finishing tubes that are reversible to extend the life of this part, which commonly is subject to the most wear. Ready-mix concrete with a 4-in. maximum slump was used. Street Services Supervisor Patrick Singleton said, “We wanted to keep the moisture content really low on this job to prevent cracking, and we let the screed do the rest of the work.

A construction joint was placed every 10 ft and an expansion joint every 200 ft. The path also is divided into lanes, with 11 ft of width for bicycles and 5 ft for pedestrians. A saw-cut joint delineates the separation and the finish is broomed longitudinally for the pedestrian portion but transversely for bicycles. At both ends of the path, as well as at two intersections along its length, sections were colored to form a decorative end cap. The path’s 6-in. thickness makes it suitable for supporting emergency vehicles and motor sweepers that may be driven over it on occasion.

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