Contributed by Rachel C. Severance, Arizona Chemical, LLC
While it is easy to take our road network for granted, it is an impressive feat of engineering that must be continually serviced, maintained, and expanded. According to the Federal Highway Administration, 4.07 million miles of paved roads existed in the United States as of 2010, the most recent year for which they have released statistics.1 In 2010 alone, the Federal highway program invested $28.4 billion for the improvement of 85,597 miles of highway, of which only 1391 miles were new highway construction.2 Pavement preservation over new construction is emphasized at the federal, state, and local government levels.
Building and maintaining our national road network comes at a cost. Asphalt pavement is engineered using specific combinations of stone and sand, held together by a binder. These virgin stone, sand, and other aggregates must be mined, crushed, sieved, and transported to asphalt mix plants with an extensive expenditure of energy and a high environmental impact. The virgin asphalt binder is produced via petroleum fractionation and distillation. Later, during maintenance and reconstruction, waste is generated during milling or removal of existing pavement layers.2,3 This waste, now called reclaimed asphalt pavement (RAP), was historically transported to landfills, or was recycled as an aggregate replacement on road shoulders, in sub-base pavement layers, and in other similar applications.
However, just using RAP as gravel or so-called “black rock” sacrifices the inherent bitumen content. As such, many road producers incorporate RAP into new hot mix asphalt (HMA) to regain value from the bitumen coating the aggregate.
Currently, it is not uncommon for new hot mix asphalt (HMA) to contain 20% RAP.4 Research is ongoing by industry trailblazers to develop and implement an appropriate and sustainable technology to use more than 30% RAP.5 However, despite specification allowances, increasing RAP use above 10-25% requires additional knowledge and technology above that of typical new construction.
A major barrier to using reclaimed asphalt materials is the effect aging has on asphalt binder properties. The aging mechanism is complex, and is visible in both binders and mixes. On a chemical level, oxidation and modification is occurring, which leads to the binder becoming harder and more prone to failure.6,7 While this stiffening provides some advantages such as resistance to permanent deformation, the binder within the RA will also be more brittle and thus more susceptible to cracking.5,8
Arizona Chemical Company, LLC, has a strong history of providing sustainable solutions from renewable resources. AZC drew on this background to specifically develop a pine-based performance additive to address the unique chemical and mechanical needs of pavement engineering utilizing recycled pavement. This SYLVAROAD™ RP 1000 performance additive bridges the technology gap and enables the use of high reclaimed content roads.9,10
Samples showing relative quantities of virgin asphalt materials on left compared to use of reclaimed materials with SYLVAROADTM on the right.
Beyond the performance benefits, there are a number of advantages to using pine derivatives for asphalt rejuvenation. The first benefit is the replacement of non-renewable, petroleum-based products with one which is green and is classified as a non-hazardous chemical. Second, the unique chemical composition resulting from upgrading a pine feedstock enhances compatibility with the asphalt, ensuring that the additive will remain miscible throughout the lifetime of the pavement. Third, the nature of Arizona’s bio-refining and upgrading process ensures a product with a highly consistent rheological effect within asphalt, which simplifies dosage and formulation for our customers.
Arizona Chemical’s innovative SYLVAROAD™ RP 1000 Performance Additive was used in the construction of the roads and parking lot around the company’s new Science & Technology Center in Savannah, Georgia, which opened in 2014.
(1) Federal Highway Administration Office of Highway Policy Information. Public Road Length - Miles by Functional System (Table HM-20) https://www.fhwa.dot.gov/policyinformation/statistics/2010/ (accessed Apr 25, 2014).
(2) American Road and Transportation Builders Association. Transportation FAQs http://www.artba.org/about/transportation-faqs/faqs/.
(3) Townsend, T. G.; Brantley, A. Leaching Characteristics of Asphalt Road Waste (Report #98-2); Gainesville, FL, 1998.
(4) Copeland, A. Reclaimed Asphalt Pavement in Asphalt Mixtures : State of the Practice (FHWA-HRT-11-021); McLean, VA, 2011.
(5) Zaumanis, M.; Mallick, R. B.; Frank, R. In TRB 2013 Annual Meeting; Transportation Research Board: Washington, DC, 2013.
(6) Read, J.; Whiteoak, D. The Shell bitumen handbook; Hunter, R. N., Ed.; Fifth.; Thomas Telford Publishing: London, 2003.
(7) Petersen, J. C. A Review of the Fundamentals of Asphalt Oxidation (E-C140); 2009; Vol. E-C140.
(8) Karlsson, R.; Isacsson, U. J. Mater. Civ. Eng. 2006, 18, 81–92.
(9) Grady, W. L.; Overstreet, T.; Moses, C. D.; Broere, D. J. C.; Porot, L. Rejuvenation of Reclaimed Asphalt. WO2013163463 A1, PCT/US2013/038271, 2013.
(10) Severance, R. C.; Grady, W. L.; Broere, D. J. C.; Porot, L.; Overstreet, T. Rejuvenation of Reclaimed Asphalt. WO 2013163467 A1, PCT/US13/38277, 2013.
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