Sustainable Land Development Today - June 2008 - (Page 10)

PAVEMENTS D 10 June 2008 Meets the Road help prevent draindown during storage and transportation of the mix. Testing the draindown characteristics of a mix is very important for porous asphalt mixes. A supplier in the Chicago area, Seneca Petroleum, offers what is called a “terminal-blended” asphalt-rubber (AR), which incorporates recycled, ground tire rubber (GTR) in the standard neat AC. Where the Rubber By Frank Hill Crumb rubber content proves to be a key porous asphalt ingredient in successful Chicago Green Alley program. The crumb rubber takes the place of polymer additives, according to Cindy Williams, quality assurance manager for the Chicago Department of Transportation (CDOT). Polymers exist in both natural and synthetic rubber. “They have an additive to help keep the crumb rubber suspended in the liquid,” Williams said, which allows for uniform blending later when it is added to the aggregate at the plant during the hot-mix process. There are two process for adding GTR to hot-mix asphalt (HMA) – dry process and wet process. In the dry process the GTR is added to the mix like an aggregate at the hot-mix plant. In the wet process the GTR is blended with the asphalt cement and is then metered into the mix at the HMA plant like AC. The wet process is the most common process used in the U.S. Terminal blended AC is a “wet” process. When the producer orders a tanker of this AC, it arrives at the hot mix plant ready to go. The plant doesn’t have to do any modifications. Stone-matrix asphalt with GTR being placed on North Avenue Bridge in Chicago Despite perceived problems following a federally mandated program in the 1990s, rubberized asphalt has proven to be one of the biggest success stories in a highly successful Chicago program. The results have been so positive that Chicago officials are looking for other ways to incorporate the rubberized formula in more traditional pavement applications. The Chicago Green Alley program started as a pilot project to address stormwater run off problems for both residents and the City. The program incorporates three porous pavement systems: asphalt, concrete and pavers. The open-graded mixes that allow water to pass through the asphalt and concrete products require specific formulas and processes. Typically a hot-mix porous asphalt uses polymer modified asphalt (PMA) and/or fibers (mineral or cellulosebased) to improve performance. The PMA increases the stiffness of the mix at high temperatures. Both PMA and fibers Sustainable Land Development Today

Table of Contents Feed for the Digital Edition of Sustainable Land Development Today - June 2008

Sustainable Land Development Today - June 2008 Contents Our Voice Editorial Board SLDT Resources Where Rubber Meets the Road Integrated Planning: The Key To Developing Sustainable Planned Communities Win-Win For College and Community Industry Spotlight: Transoft Unique Organization, Unique Opportunity New Preferred Provider Comments from the Austin Conference Welcome New Members New Knowledge Project Articles Books Going Green Business Management Risk Management Surveying and Mapping Industry News Products/Services Showcase Advertiser Index Classifieds The Last Word

Sustainable Land Development Today - June 2008

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