Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85927
"The use of high percentages of RAP with WMA looks promising and should be considered for selected field projects if additional research supports this effort," they conclude. Surfactants Exhibit Anti-Strip In the meantime, surfactant-based warm mix additives can feature an anti- strip function. Rediset LQ from AkzoNobel Surface Chemistry allows a reduction in mixing and paving temperatures while providing built in anti-stripping effect, the manufacturer says, while also being used as a compaction aid for hot and warm mixes. Rediset LQ allows the asphalt mixing temperature to be reduced (by 25 to 55 degrees F) while ensuring good coating and workabil- ity. "Mixes prepared with Rediset LQ meet moisture resistance requirements without the need for additional liquid adhesion promoter," Akzo says. And last year, use of Evotherm 3G from MeadWestvaco enabled the U.S. Army Corps of Engineers to preclude use of lime as anti-strip modifier in an open- graded porous asphalt pavement. At the Marine Boot Camp at Parris Island, the U.S. Army Corps of Engineers did not have a specification for an open-graded porous asphalt mix, so it studied specs of the South Carolina DOT, says Dean Frailey, business development manager, MeadWestVaco Asphalt Innovations. "They opted to go with South Carolina's OGFC standard," he said. "It's a large- stone mix, with 6 percent polymer modified PG 76-22 asphalt binder. Typically, with a mix like this they would put in lime as a stabilizer, adhesion promoter, and for protection against moisture susceptibility, and then add fibers." Use of the WMA additive greatly simplified things. "They opted to remove the fibers and remove the lime while using the Evotherm warm mix technol- ogy. Since both fibers and lime were removed, they added back 8 percent washed screenings to act as fines in the mix," Frailey says. "The additive fights moisture susceptibility, promotes adhesion and blocks drain down. It's very unique for this application." Premature Aging Diminished In the hot mix plant, the heat contributes to premature or artificial aging of the binder, which breaks down the liquid asphalt even as HMA is produced. This gives pavement oxidation a head-start which gets worse as the mix ages in-place over time. Low energy WMA may enhance pavement durability, because with lower production temperatures, the valuable, lightest hydrocarbon fractions from liquid asphalt in the mix aren't driven off by the heat of the burner. Thus the lower heat precludes "premature aging" of binder, with a goal of reducing pavement thermal cracking. "By lowering the temperature of production, we are avoiding some of the po- tential degradation to binder that can occur at higher production temperatures," says Everett Crews, Ph.D., technical manager for MeadWestvaco. Evotherm is dif- ferent from other warm mix technologies in its ability to produce mixes around 200 degrees F, Crews says. "Other warm mix technologies produce material at temperatures up to 260 degrees Fahrenheit," he says. "Evotherm is unique in that we can push the limit lower. We have made mixes at below 200 degrees F that have performed very well." v Write 172 on Reader Service Card or visit www.betterroads.com/info Towmaster_BR0312pg27.indd 1 Better Roads August 2012 25 2/21/12 9:36 AM