New Fine PFC Offsets Bleeding, Flushing on Roadways
Lufkin had a problem.
The highway interchange at US 59 and Loop 287 is one of the busiest in the area. Trucks wanting to avoid Lufkin traffic exited US 59 to Loop 287. The volume of traffic, the weight of the vehicles, and the speeds when exiting were taxing the sealcoat surface. It was bleeding and flushed. (Bleeding and flushing occur when hot weather causes the asphalt binder to expand onto the pavement surface, creating a slicker surface that can promote sliding.) When it rained, friction was low, which resulted in vehicles sliding off the road. Attempts at placing conventional hot mix resulted in shoving (a pushing or rippling of the pavement caused by braking) due to the high shear forces.
Tom Scullion, manager of the Texas A&M University Transportation Institute’s (TTI’s) Flexible Pavements Program, and Cindy Estakhri, manager of TTI’s Recyclable Materials Program, were looking for some test locations for three new thin asphalt mixes they had created: a crack-attenuating mix (CAM), fine-graded stone matrix asphalt (SMA) and permeable friction course (PFC).
The Lufkin location seemed like a good place to test the fine PFC, which can be used to cover bleeding sealcoats and is particularly useful where wet-weather accidents occur. Could thin asphalt stand up to the pounding it would take at this intersection? “The Lufkin District picked the location, which was the most severe application that could have been chosen. We were nervous about it. This was really, really going to test the performance of it,” Estakhri says.
The surface was laid at the beginning of summer 2011, which turned out to be one of the hottest on record in Texas, with a record number of 100°-plus days. “If the fine PFC was going to tear or shove under those shear forces, it would have done it. It didn’t. It held up really well,” Estakhri reports.
Now, two years later, how is it performing? Tom Hunter, director of construction for the Lufkin District of the Texas Department of Transportation (TxDOT), says, “It’s holding up well under all that southbound US 59 traffic.” Hunter notes that the surface only has to last one more year, as new north- and southbound flyovers are currently being constructed to replace the existing intersection.
How about automobiles sliding off the road? “We still have some drivers who slide off the highway, but this surface has definitely reduced that number. It must be the surface, because I don’t think the drivers have changed. We have some people who go way too fast. It wouldn’t matter what surface we put down there for them,” Hunter says.
Estakhri thinks that thin-coat PFC is the answer to many maintenance problems. “We have a lot of confidence in the mix itself. It has more air voids in it than conventional PFC. It should drain better. Durability is not an issue. The mix will hold up. Because of the high air void content, it should drain better and get water off the road,” she said.