Asphalt is the sticky black residue that is left over from the processing of crude oil. It has been used in paving for more than a hundred years. When asphalt first came into use, oil refiners would give it away. Today, however, it is a highly traded commodity that demands premium prices. These prices have increased dramatically. In 2002, asphalt sold for approximately $160 per ton. By the end of 2006, the cost had doubled to approximately $320 per ton, and then it almost doubled again in 2012 to approximately $610 per ton.

The rising price of asphalt had a major impact on the cost of constructing pavements, which increased interest in finding ways to reduce costs. Methods to reduce costs include minimizing the amount of asphalt in the mix, increasing the use of reclaimed asphalt pavement (RAP), and replacing part of the asphalt with lower cost additives. RAP already contains asphalt, albeit aged material that does not have the same properties of fresh asphalt.

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The DSR tests binder placed between two parallel plates about the size of a quarter. One of the plates moves and the machine measures the viscoelastic properties of the asphalt. The DSR is used to determine the maximum high temperature performance grade (PG) in degrees Celsius. These temperatures increase in steps of 6 degrees and are typically PG 52, 58, 64, 70, 76. They provide a maximum service temperature for the pavement. For example, a PG 70-28 binder would have a maximum service temperature of 70 degrees Celsius and a minimum service temperature of minus 28 degrees Celsius.

The addition of soft materials to asphalt will reduce the high temperature grade (for example, from a PG 76 to a PG 70). Several additives have been evaluated by industry and academia, including used frying oil, residues from corn stover, and even treated swine manure, for this purpose.

Analysis of liquid asphalt for the trace metals calcium, copper, zinc, and molybdenum provides a measure of the amount of REOB present. Sulfur and iron could also be analyzed, but because they occur naturally in asphalt, their use would confuse the analysis.

Because REOB is a waste product, its composition varies widely not only between producers but also between samples from the same producer on different days. The compositional analysis is also affected by the asphalt into which it is blended. However, by making many blends using different REOB samples and different asphalt binders, the variations largely can be averaged out.

Several States provided samples of known REOB composition to TFHRC researchers, who analyzed the samples to compare the percentage of added (known) REOB to the found (tested) amount. The analyses showed a comparable percentage of added and found REOB.

To execute the plan, TFHRC provided the initial test method and 45blends of various REOB modified asphalt binders with REOB concentrations of 2, 5, 8, 10, and 20 percent. In total, the researchers prepared and shipped 720 blends.

The participants are testing the samples independently using the guidelines provided by the TFHRC researchers. The round-robin testing is nearly completed, and TFHRC is in the process of collecting the results. The output will be a proposed AASHTO test method that any State can adopt and use.

The unanswered question that remains is whether REOB negatively influences pavement life. In the United States, very little evidence is available, perhaps because no State highway agencies knew their binders contained REOB until recently. However, research in Canada linked the premature failure of Highway 655 in Timmins, Ontario, with the presence of REOB.

The overnight temperature in the area can reach as low as -40 degrees F (-40 degrees C). The pavement without REOB on one segment of Highway 655 showed no distress after 9 years of service. The pavement with REOB, which is located 0.6 mile (1 kilometer) from the pavement without REOB, has identical subgrade, traffic density, and climate. However, the segment of Highway655 with 5 to 10 percent REOB showed significant cracking. In this example, the presence of REOB was the identified cause of cracking at a low temperatures.

Similarly, a section of test pavement in Minnesota (MN1-4) found to contain REOB also cracked prematurely. The pavement performed well for the first 3 to 4 years, but then started to crack. This pavement is also subject to low temperatures.

The TFHRC researchers carried out a few mix tests (mixing the binders with aggregate) in 2015. The tests were not extensive, but they showed that at levels of 6 percent or more, the tensile strength of the asphalt dropped significantly. At a level of 3.5 percent REOB, the variation in the physical test methods was greater than the effect of REOB. In fact, it was difficult for researchers to assess whether REOB was present.

At TFHRC, researchers are planning a different way of looking at asphalt binders. Previously, all asphalt testing measured engineering properties such as stiffness. These tests do not show what materials had been added to the asphalt.

One sample received during the TFHRC study had a very strange analysis. The sample had the following test results: Superpave PG 64-28 with a high temperature grade of 67.3 Tcritical on the bending beam rheometer was 6.7 degrees Celsius. Chemical analysis indicated it contained approximately 1.7 percent phosphoric acid, 10 percent ground tire rubber, and 19 percent REOB. The addition of 1.7 percent phosphoric acid likely would make the asphalt very stiff. Ten percent ground tire rubber would make it even stiffer. Then 19percent REOB would soften it and bring it back within specification.

These results demonstrate there are weaknesses in the standardized engineering testing protocols that may be exploited. The producer may have an economic benefit and the product passes all the standardized tests, but the product may not be beneficial to ensuring long-term performance.

To address this issue and the expansion of new asphalt additives and extenders, TFHRC is starting a research program to use handheld spectroscopic devices, x-ray fluorescence spectroscopy, and Fourier transform infrared spectroscopy to enable analyses to be done in the field rather than having to take samples back to the lab. Fourier transform infrared spectroscopy can even find lime in the mix, as well as styrene-butadiene-styrene and styrene-butadiene rubber polymers. X-ray fluorescence spectroscopy can find REOB and phosphoric acid, and the handheld spectroscopy works for spot checks. These instruments can be preprogrammed and require no additional training or skills for operators. All of this testing can be done directly from the paving machine, or at the asphalt plant by an unskilled operator, saving time and associated costs. These methods are much more difficult to manipulate because they can almost always tell what materials have been added to the mix. They also enable the possibility of field spot checks and eliminate the possibility of sampling errors where the asphalt being used was not the same as received by the testing lab.

The TFHRC team will soon submit to AASHTO the draft test methods that transportation agencies can use to test for the presence of REOB in asphalt mixes.These test methods will help transportation agencies know what materials and additives are present in the asphalt mixes they are purchasing.

Asphalt pavements deliver the performance that agencies, designers, owners, and drivers demand. A solution for the entire transportation network, asphalt is a completely recyclable material that delivers a safe, smooth, quick-to-construct pavement optimized for costs, community, and environment. Asphalt roads are proven solutions that work for your budget, community, and future. Paving with asphalt delivers immediate benefits today while looking out for tomorrow.

Asphalt is flexible, adaptable, versatile, customizable, and ready to meet just about every pavement need. With the option of nighttime construction and without the lengthy curing time typical of concrete, asphalt pavements offer the flexibility needed to handle all levels of traffic, and they can be maintained or repaired quickly.

The asphalt industry innovations continue to afford asphalt pavement as the most economical, efficient, and environmentally friendly pavement. Asphalt engineers are constantly innovating to make roads perform for today and the future. The asphalt industry is committed to workforce training and to scientifically analyzing pavements to ensure the best products.

Did you know that over 90 percent of the roads in America are surfaced with asphalt? For those who know the benefits of asphalt, there is no substitute. Asphalt pavement, right for America, right now and into the future.

The Role of Asphalt in Livable Communities acknowledges the momentum toward creating more livable communities and details the versatility of asphalt pavements and sustainable qualities that make it a natural source for advancing the goals of livability.

Asphalt has always been and continues to be the pavement of choice for America. This brochure discusses the benefits of the product and why asphalt is right for America, right now and into the future.

NAPA advances the asphalt pavement industry through leadership, stewardship, and member engagement to support sustainable transportation infrastructure that paves the way for thriving communities and commerce.

NAPA is the only national trade association that serves the asphalt pavement industry. Membership is available to any asphalt pavement mix producer, paving contractor, equipment manufacturer, material supplier, equipment distributor, engineering firm, or consultant.

Stay on top of industry best practices and news by plugging in to our communication channels. From social to traditional media, we deliver information on a variety of platforms to keep you abreast of the latest issues and trends impacting the industry. 18c6514909

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