First test project
With the producer onboard, the department began with a test project: paving a section of its own property used for parking heavy-duty equipment and salt storage. It placed 6 inches, compacted it, and left the surface unfinished to monitor its durability. The pavement performed so well, the department didn’t hesitate to use it as a base course for city streets. “We placed the test pad in 2009, and it’s still in good shape,” Mann says.
Although it’s too soon to measure long-term maintenance savings, Mann anticipates repairs will be easier with the RCC-and-asphalt streets. “With the concrete base course, we can go in and mill off the top couple of inches, but we shouldn’t have to do anything else,” he says.
One unexpected development has been the controlled cracking pattern of the asphalt surface over the RCC base. “Typically, when asphalt cracks, it’s in a random way,” says Mann. “But here, we’re seeing surface cracks that mirror the joints we’ve cut in the RCC base course. We still have to seal them, but it’s actually easier since they follow a more predictable pattern.”
This is one reason the village prefers to top RCC with asphalt. According to Adaska, due to the absence of air entrainment, unsurfaced RCC in freeze/thaw environments is more susceptible to surface scaling and frost damage than conventional air-entrained concrete pavement. The rough surface doesn’t pose a problem in industrial areas, but is less desirable for public streets.
When topped with asphalt, however, an RCC road base can last up to 50 years, compared to the 10-to-15-year lifespan of typical full-depth asphalt. “RCC actually improves the life of the asphalt by preventing the fatigue failure that occurs with asphalt on a stone base,” says Adaska.
Adding an asphalt overlay to an RCC base is also easier for public agencies to handle in-house. “Like most cities, we don’t have the equipment to finish concrete pavement, so we’d have to pay a contractor, which would negate some of the cost savings,” says Mann.
Unfinished RCC roads are typically built by counties or state DOTs that can use their own diamond grinding equipment to smooth the surface. “Diamond grinding smooths out the pavement, removes high stops, and provides an improved surface texture for enhanced skid resistance,” says Adaska. “A finished RCC surface also takes advantage of concrete’s higher reflectivity, producing a cooler pavement with reduced lighting requirements.”
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