Pounding the Pavement

Next time you grow weary of driving over the same stretch of pavement on the way to work every day, consider the task ahead of engineer David Bush. As the local manager of a new Caltrans project, he has to cover one chunk of the Antelope Valley Freeway all day, every day, for the next two years.

Of course, he doesn’t have to do it in a beat-up Corolla like the rest of us. His wheels are an orange 70-ton behemoth nicknamed Susie, one of two Heavy Vehicle Simulator trucks purchased by Caltrans for about $1 million apiece to research pavement design.

Armed with a crew and a trailer full of gadgets, Bush will run the state’s monster truck back and forth thousands of times over 26-foot-long strips of concrete. Eventually the crew will test about 1,400 feet of roadway.

Changes in the pavement’s temperature and structure will tell researchers how it will hold up to years of wear and tear under 18-wheelers. But with Susie running about 5 mph, it’s going to be a long two years.

“ ‘Boring’ is relative,” Bush said. “There’s always something to do here.”

Caltrans officials say the need to develop stronger, faster-setting pavement is urgent. The agency is already spending $300 million a year to patch up California’s dilapidated, 1950s-era freeway network, which is well beyond its intended life.

State officials plan to allocate $600 million a year for the next seven years to rehabilitate freeways statewide. Of utmost concern are truck lanes and freeways frequently used by big rigs, including the Golden State, Pomona and Long Beach freeways.

Caltrans researchers are seeking the equivalent of the better mousetrap: a more durable, faster-drying concrete that will shorten the time it takes to lay the new pavement and minimize traffic congestion that associated with construction work.

Caltrans purchased the two hydraulic-powered simulators in 1994, but have used them only for small-scale tests in controlled environments, said agency research chief Wesley C. Lum. The Palmdale experiment marks Susie’s first field test, he said.

Still, the crew must exercise a certain degree of control over the pavement to measure the effects of the pressure. They have erected an insulated enclosure around the test area to keep the concrete at 68 degrees. Each time they shift to a different sliver of road, they must break down and reassemble the enclosure, which takes at least a day.

Once the surroundings are set, the crew fires up the 74-foot-long vehicle and rolls its heavy test wheel over the pavement. Researchers can vary the weight of the wheel from 4,500 pounds to 22,500 pounds to simulate truck traffic.

During the research project, the Caltrans crew--which includes experts from Dynatest Engineering and South Africa’s Council on Scientific and Industrial Research--will test two 700-foot sections of concrete with varying thicknesses, widths and strengths.

Results of earlier tests have prompted the agency to change design specifications to require contractors to compact freshly laid concrete to a precise point, and to require a sticky bonding material to be applied between layers of concrete, Lum said.

Data from the Palmdale tests will be shared with Federal Highway Administration researchers using automated trucks to study asphalt on a two-mile track near Reno, Nev., he said.

“The real key here is being able to take the results from this and improve how we do things,” he said. “We constructed [the state’s freeways] 30 or 40 years ago. The time to replace them is now.”

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A Truck Named Susie

A giant Heavy Vehicle Simulator truck will be used to evaluate new pavement designs in a Caltrans test area on the Antelope Freeway. The truck was named Susie by a former operator.

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Weight: 70 tons

Engine: 10 cylinder diesel

Built: 1973 in South Africa

Current owner: Caltrans

Price: $1 million (in 1994)