Asphalt, Self-Healing Asphalt
Asphalt dominates the United States—its presence is mostly unavoidable. Asphalt’s original function in ancient times served as waterproofing as it is still does today; however, the function of asphalt cement commands the asphalt market –“In the United States, 85% is used for roads”1. In 1837 Richard Tappin Claridge held the first patent for asphalt pavement in the United Kingdom.2 The composition of asphalt cement appears comparable to concrete—ratios of dry ingredients (sand and aggregate) are mixed with a liquid immediately prior to its installation on site. However, while concrete has Portland cement and water, the dry ingredients of asphalt are bound with cement and liquid asphalt—a byproduct of crude oil. Because oil acts as the bonding agent, asphalt repels water and proves more resilient to continued use than concrete. In addition, “asphalt is 100% recyclable,” meaning an asphalt tumbler can reheat once laid road, and “after approximately 20 minutes of heating the hot mix asphalt is typically 300F and ready for laydown using conventional techniques.”3 (An ease in construction which undoubtedly lends to its overabundance). However, according to Erik Schlangen in his 2012 TED Talk on “A self-healing” asphalt,” “…you can have a lot of splash water with the asphalt” in addition to being “a noisy material”—meaning drainage with nonporous asphalt is poor, as well as, noise resulting from cars driving upon the surface—hence the creation of its porous offspring that eliminates both problems.4 What does rise as a problem with porous concrete is the concept of “graveling,” or the bitumen binding the aggregate together wears over time and the individual components break apart. Schlangen’s “self-healing” aggregate uses induction heat to bind the existing bitumen with new steel wool. To put this into practice, Schlangen concludes that “if we go over the road every 4 years [with the induction machine] we can double the surface life of this road which saves a lot of money.”4
1. “Is Self-Healing Asphalt the Road of the Future?” Dykes Paving and Construction RSS. Web. 23 Aug. 2013.
2. “Asphalt.” Wikipedia. Wikimedia Foundation, 17 Aug. 2013. Web. 23 Aug. 2013.
3. “Asphalt Recycling.” Asphalt Recycling. Web. 23 Aug. 2013. <http://www.asphaltrecycling.com/display.php?cnt_id=24>.
4. “Erik Schlangen: A ‘self-healing ’ Asphalt..” TED: Ideas worth Spreading. Web. 23 Aug. 2013.