Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/634023
EquipmentWorld.com | February 2015 49 highway contractor | by Chris Hill | ChrisHill@randallreilly.com A sphalt pavement pres- ervation is a tactic used primarily in the realm of low-volume road- ways. It has helped municipalities expand road life, keep overall highway maintenance costs down, and keep residents rela- tively happy during their commutes to and from work and home. The success of these programs, along with interest from the Federal Highway Administration, is now pushing the paving industry to focus on pavement preservation for high- volume roadways. The National Center for Asphalt Technology (NCAT) at Auburn Uni- versity is leading the way, imple- menting pavement preservation test plots on U.S. 280 in central Alabama. The highway is a major artery into the metro Birmingham area. (See sidebar "High-volume preservation method testing.") NCAT directed placement of these plots last summer, collecting per- formance data such as roughness, rutting and cracking. In addition to collecting this data weekly, they are also studying more long-term perfor- mance metrics (such as field perme- ability) on a quarterly basis. The test is designed to be a "ratio- nal starting point," in order to narrow down which pavement preservation techniques are the optimal combina- tion of life-cycle costs and perfor- mance. The secondary goal is to use the data gathered to create guide specifications, and to recommend UNTAPPED POTENTIAL FOR CONTRACTORS High-volume pavement preservation: High-volume preservation method testing As part of its high-volume roadway testing, NCAT is examining 34 treatments and treatment combinations on test strips measuring 1/10 of a mile on U.S. 280 in central Alabama. These sections include a combination of the following: Microsurfacing: This treatment, which is slowly becoming the high-volume treatment of choice, is a slurry made up of a polymer-modified emulsion, fine aggregate, cement and water. It requires special equipment to mix and spread the product; an expenditure that seems to be precluding some contractors from using this method. Crack sealing: As simple as it sounds, applying a water-proof compound to cracks is one of the least esthetically-pleasing treatments, but it's perhaps the most economical, particularly with the cost of material. Richard Turner, of Charleston County Transportation Dvelopment, says he's working toward using crack sealing in combination with a fog seal as part of his pilot project program. "It's something we need to do and it'll be a cost effective treatment, but we've been slow to push that one out – because it's not pretty." Chip seal: This method is one of the longest-used preservation techniques, and involves the application of an asphalt spray with aggregate placed on top. Histori- cally, it has been used on low-volume roadways. Most of Comer Contracting's preservation work in Connecticut has involved chip seals. Fog seal: A mixture of water and a sealant, primarily used on shoulders or patched areas. Like chip seals, it's generally for low-volume surfaces. Scrub seal: Closely related to a chip seal, this method requires brooms to shove an emulsion and aggregate mix into pavement cracks and crevices. Scrub brooms are towed by the truck applying the mix. Cape seal: This is a chip seal with a microsurfacing overlay. Marty Comer, with Comer Contracting, says he's found this to be more widely accepted than a chip seal alone, particularly in residential areas. Again, this has been used more on low- volume roadways. Thinlay (thin asphalt overlays): This is a growing method of preservation for both low- and high-volume highways. Small aggregate, flexible binders, and a thin mat (of 3/4-inch to 1-inch) are the key features. Using typical asphalt paving equip- ment, contractors can easily add this method to their preservation toolbox. Cold recycling: This involves milling and mixing recycled asphalt pavement with an emulsification or rejuvenating compound, and then laying down a mat from the mix. This preservation method can be used for both low- and high-volume roadways.