The hottest trend in the road-building business got a little cooler, and everyone's delighted. Contractor Knife River Corporation recently completed a 9-mile freeway repaving job on Interstate 5 west of Chico utilizing warm mix asphalt (WMA), with excellent results.
"Warm mix" asphalt can be produced at lower temperatures than conventional asphalt and promises to dramatically reduce oil consumption, a major ingredient in asphalt, as well as air pollution. Used for many years in Europe, Warm Mix Asphalt is gathering momentum in the United States. The National Asphalt Pavement Association estimates that within five years, half of all asphalt produced in the United States will be of the warm-mix type.
According to Caltrans District 3 Material Engineer Joseph
Peterson, the $5.4 million pilot project was on the southbound lanes of Interstate 5 from the county line just north of Orland, with a total lane-miles length of 36 miles. The project called for removing the existing Open Grade Friction Course (OGFC) asphalt, and replacing it with 0.10' Rubberized Hot Mix Asphalt-O (RHMA-O). The project tonnage was approximately 18,000, and the WMA technology used was MeadWest Vaco Corporation "Evotherm" at 5.0 percent of Bitumen by weight. Paving work (pictured) wrapped up on May 21.
"Telfer Oil Company of Martinez provided the Evotherm™ WMA additive and equipment for this project"
The Hot Mix Asphalt (HMA) design was performed by Caltrans North Region Materials Branch, headquartered in Marysville. Peterson said the initial OGFC mix design was performed per the California Test Methods. OBC was 5.5 percent by dwa. The multiplier used was 1.3 and was determined in the lab by producing RHMA-O at 1.3 and 1.4 multiplier.
Peterson said each mixture was examined for aggregate coating and flushing. It was determined that the 1.3 multiplier produced a more uniform product. The production RHMA-O binder content was set at 7.2 percent by dwa.
WMA production started at 320 Farenheit, with approximately 200 tons placed. Then the production temperature was dropped to 300 F and ran the balance of the day (2,200 tons produced). Peterson said that for the next three days the production started at 300 F and at noon dropped the production temperature to 290 F for the balance of the day.
Day five of paving production started at 300 F at noon, and was dropped to 290 F and then at 1:30 p.m. dropped again to 285 F. Approximately 200 tons were placed at 285 F, and then production resumed at 290 F.
"The product at all temperatures placed easy, with breakdown temperatures ranging from spec 285 F all the way down to 250 and final from about 260 to 235," Peterson said in an e-mail report. "Chunking in the windrow or mat was really non-existent. Smoke-wise, there was very little, and as expected the lower the temperatures, the less smoke there was."
Knife River Quality Control Manager Tim Denlay said the I-5 job was his company's first major foray into WMA in California. Previously, the company produced and placed test sections using Akzo Nobel "Rediset" at its Chico Plant, and the roadway has held up well under heavy truck traffic.
Denlay said the I-5 job was missing one element that evaluators were looking for: the impact on the mix of a long haul. In the case of the I-5 job, the Knife River plant was within the project limits. Denlay hopes to be able to do another project this year with a two-hour haul distance to gauge how the asphalt performs under those conditions.
The mix as it was placed on the jobsite in windrows seemed "alive," Denlay said, there was no chunking or other problems associated with placement. Smoke at lower temperatures was greatly reduced. A photo of the paving operation supplied by Caltrans showed steam rising off the newly resurfaced roadway, rather than smoke, Denlay said.
An added environmental benefit to the project was that the "rubberized" asphalt utilized recycled rubber. According to Denlay, the binder design shows 81.5 percent PG64-16 which includes extender oil and 18.5 percent total CRM, of which 75 percent is scrap tire and 25 percent is high natural. Denlay says Knife River ran 7.2 percent by dry weight of aggregate rubberized asphalt on most of the project. That works out to about 1,200 tons of rubberized asphalt, of which about 14 percent is scrap tires. The bottom line is about 168 tons of scrap tires were used to resurface the roadway rather than ending up in a landfill.
"Warm mix" asphalt can be produced at lower temperatures than conventional asphalt and promises to dramatically reduce oil consumption, a major ingredient in asphalt, as well as air pollution. Used for many years in Europe, Warm Mix Asphalt is gathering momentum in the United States. The National Asphalt Pavement Association estimates that within five years, half of all asphalt produced in the United States will be of the warm-mix type.
According to Caltrans District 3 Material Engineer Joseph
Peterson, the $5.4 million pilot project was on the southbound lanes of Interstate 5 from the county line just north of Orland, with a total lane-miles length of 36 miles. The project called for removing the existing Open Grade Friction Course (OGFC) asphalt, and replacing it with 0.10' Rubberized Hot Mix Asphalt-O (RHMA-O). The project tonnage was approximately 18,000, and the WMA technology used was MeadWest Vaco Corporation "Evotherm" at 5.0 percent of Bitumen by weight. Paving work (pictured) wrapped up on May 21."Telfer Oil Company of Martinez provided the Evotherm™ WMA additive and equipment for this project"
The Hot Mix Asphalt (HMA) design was performed by Caltrans North Region Materials Branch, headquartered in Marysville. Peterson said the initial OGFC mix design was performed per the California Test Methods. OBC was 5.5 percent by dwa. The multiplier used was 1.3 and was determined in the lab by producing RHMA-O at 1.3 and 1.4 multiplier.
Peterson said each mixture was examined for aggregate coating and flushing. It was determined that the 1.3 multiplier produced a more uniform product. The production RHMA-O binder content was set at 7.2 percent by dwa.
WMA production started at 320 Farenheit, with approximately 200 tons placed. Then the production temperature was dropped to 300 F and ran the balance of the day (2,200 tons produced). Peterson said that for the next three days the production started at 300 F and at noon dropped the production temperature to 290 F for the balance of the day.
Day five of paving production started at 300 F at noon, and was dropped to 290 F and then at 1:30 p.m. dropped again to 285 F. Approximately 200 tons were placed at 285 F, and then production resumed at 290 F.
"The product at all temperatures placed easy, with breakdown temperatures ranging from spec 285 F all the way down to 250 and final from about 260 to 235," Peterson said in an e-mail report. "Chunking in the windrow or mat was really non-existent. Smoke-wise, there was very little, and as expected the lower the temperatures, the less smoke there was."
Knife River Quality Control Manager Tim Denlay said the I-5 job was his company's first major foray into WMA in California. Previously, the company produced and placed test sections using Akzo Nobel "Rediset" at its Chico Plant, and the roadway has held up well under heavy truck traffic.
Denlay said the I-5 job was missing one element that evaluators were looking for: the impact on the mix of a long haul. In the case of the I-5 job, the Knife River plant was within the project limits. Denlay hopes to be able to do another project this year with a two-hour haul distance to gauge how the asphalt performs under those conditions.
The mix as it was placed on the jobsite in windrows seemed "alive," Denlay said, there was no chunking or other problems associated with placement. Smoke at lower temperatures was greatly reduced. A photo of the paving operation supplied by Caltrans showed steam rising off the newly resurfaced roadway, rather than smoke, Denlay said.
An added environmental benefit to the project was that the "rubberized" asphalt utilized recycled rubber. According to Denlay, the binder design shows 81.5 percent PG64-16 which includes extender oil and 18.5 percent total CRM, of which 75 percent is scrap tire and 25 percent is high natural. Denlay says Knife River ran 7.2 percent by dry weight of aggregate rubberized asphalt on most of the project. That works out to about 1,200 tons of rubberized asphalt, of which about 14 percent is scrap tires. The bottom line is about 168 tons of scrap tires were used to resurface the roadway rather than ending up in a landfill.
Cathrina Barros, a senior Transportation Engineer with the Caltrans Office of Flexible Pavements, said the department will be evaluating the performance of the warm mix asphalt pavement sections versus the control sections over the next two years.
"It's going to be more of a visual assessment more than anything," she said. "Everything will be evaluated in comparison to the control sections. If it all behaves the same, that's a good thing."
Article courtesy of CalAPA May 26, 2009 Newsletter