San Antonio Asphalt Rubber Permeable Friction Course Mission Accomplished

By Douglas Carlson

While filming the RPA Quiet Pavements Video on location at IH-35 Asphalt-Rubber Permeable Friction Course project in San Antonio, I had the opportunity to interview Dale Rand, P.E., Director TXDOT, Flexible Pavement Branch, and Gary Fitts, Senior Engineer of the Asphalt Institute Regional Office which is adjacent to the project. Both had some positive things to say about the AR-PFC resurfacing of a 20 year old concrete pavement besides the unanticipated 10 dB reduction in tire pavement noise. Fitts said it was nearly impossible to hold a conversation outside the building prior to the resurfacing so he was extremely pleased with the results.
     Gary Fitts also commented on the added safety of the AR-PFC overlay compared to the previous aged concrete surface with respect to major accidents, primarily caused by water on the slick pavement. Since he had personally observed many major accidents (many multivehicle) prior to the project and noticed the reduction afterwards, curiousity led Gary to obtain traffic and incident reports from the San Antonio Police Department. The first period covered the year prior to the AR PFC overlay and the second period came from the year after the overlay. Here's what Gary said: "Prior to the overlay there were 85 major accidents and 107 days with rain. Following the overlay, there were only 48 major accidents during 144 days of rain. (See Chart below) Major accident is defined as injury accident)
     Dale Rand commented on TX DOT's obligation to make highways as safe and as comfortable as possible. "Permeable Friction Courses met these needs before with conventional asphalt, but they lacked durability.

They did not last very long. Since the development of a Permeable friction Course with Asphalt-Rubber binder," he noted, "the durability issue has been resolved." "I think the oldest AR-PFC in the TexDOT system is in the Lufkin district which is now about 11 or twelve years old. Although it does not look like a new pavement, it doesn't look very old either, you wouldn't think it was as old as it is. It does a good job a stopping reflective cracks, there aren't very many. When I'm concerned about reflective cracking, I use an AR binder," Rand said.
     On the IH-35 project in San Antonio, which has a fair amount of wet weather, Rand was looking for an overlay on a twenty (20) year old concrete surface that was rough and slick. Diamond grinding was not an option as the aggregate in the concrete polished over the years. When he made the decision to use an AR-PFC on the project, his objective was to address safety and comfort issues. Noise reduction was not a primary concern as the project is not in a residential area. One of the major factors in his decision was the high binder content of the AR-PFC. He was also concerned about a material that would stick to the polished concrete. An observation of various PFC samples at the Lab led to his decision to go with the AR-PFC. Of all the samples, only the AR binder stuck to the stainless steel surface of the Lab counter. The success of the project confirmed his decision. He said, "There are no problems with de-lamination, the AR binder solved that problem." He said the public response to the better ride, virtual elimination of water spray issues and noise reduction was extremely gratifying.



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