Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85930
"We made a trip to Georgia to see what they [Georgia DOT] were doing right," Dale Rand, fl exible pavements branch director for the Texas Department of Transportation (TxDOT), tells Better Roads. "[Geor- gia had] added cellulose fi bers and mineral fi bers and polymers to make the mixes more durable. Georgia had started placing [its] improved mixes in the early 1990s and they were seven to eight years old by the time we saw them. So we came back and tweaked our design somewhat and came up with our version, which is very similar to the Georgia version. We just call it Permeable Friction Course (PFC)." For the PFCs, Rand says Texas now uses PG 76-22 asphalt cement – polymer modifi ed – and typically 0.3 percent of cellulose fi bers. Some 80 to 100 percent of the aggregate passes the 1/2-inch sieve and 35 to 60 percent passes the 3/8-inch sieve. A minimum of 6 percent asphalt is required in Texas PFCs, and they are designed to have about 20-percent air voids, Rand says. "We typically specify them on roadways that have a history of wet weather accidents," Rand points out. "In my opinion, they are most ben- efi cial on undivided highways where you have a history of wet weather accidents. Our TxDOT offi cial policy is that we target pavements in areas to prevent wet weather accidents. We also use a number of PFCs routinely on our Interstate system. We use them on high-speed facilities, if the posted speed limit is above 45 mph." Rand says PFC mixes cost about 20 percent more per ton than con- ventional dense-graded mixes. But because the PFCs have 20 percent air voids in them vs. 7 percent in dense-graded mixes, the cost per square yard of the PFCs is roughly equivalent to the dense-graded mix- es. Typically, Rand says, TxDOT ap- plies the PFCs at 1-1/4 inches thick to 1-1/2 inches thick, with 1-1/4 inches as the typical thickness. courses (PFCs). In the late 1990s, a 2-mile section of RM 1431 near Jonestown, Texas, in the Austin District, came to be called "Dead Man's Curve" by the media and local residents. For years, the Austin District took proactive measures to reduce the number of accidents along RM 1431, but the rate of wet weather accidents remained un- changed. So TxDOT placed a story to tell about its permeable friction (TxDOT) has a notable success Department of Transportation Th e Texas PFC on RM 1431 under an emergency contract to address the number of wet weather accidents and fatalities. It worked. Th e number of wet weather accidents on this high- way dropped by 93 percent in the four years since placement of the mix in Febru- ary 2004, compared to the three-year period prior to the placement of the overlay. Better Roads September 2012 25 F i x i n g ' D e a d M a n's C u r e v '