Sustainable Land Development Today - June 2008 - (Page 12)

Close up of porous asphalt. Chicago Green Alley Program Chicago’s 1,900 miles of alleyways is comparable to the total hard surface of five mid-sized airports and nearly equal to the total lane miles of the Illinois Interstate Highway system. That’s a lot of hard, impermeable surface. Begun as a pilot project in 2006, the Chicago Green Alley program took off in 2007 with an increased demand for the benefits it offered to residents and the city. At the heart of the program are several porous pavements designs, which allow stormwater to seep into the soil and recharge aquifers, rather than run off into the city’s combined sewer system or adjacent property. The program changed the traditional paving methods that raised the crown in favor of a reverse crown to channel water to the center of the roadway. Several basic design techniques can be tweaked to fit the varying conditions of specific alleys. All but one incorporates porous pavements. The porous pavements can be used full width with a onefoot or greater sub grade of same-sized rock to hold water until it can seep away. Another technique is to pour solid concrete in the wheel paths with pervious concrete down the middle over a five-foot-deep trench lined with a waterproof membrane on either side. This “center trench” model is used to protect basements that are adjacent to the alley. Installation can be tricky because of the tight quarters and the need to create a lower roadway center. For instance, a typical vibrating screed won’t work to install the pervious concrete because the shaking action causes the cement paste to fill the voids between the aggregate. A special rolling screed has been used that acts like a weighted rolling pin. Paving stones, which have been used extensively in Europe for many years to deal with stormwater runoff, are the most established system. They also provide a different look that can be very popular with residents, especially those who had a cobble stone alleyway. The only non-permeable surface in the program is high albedo concrete, which is made with recycled slag from ore-smelting operations to make it lighter in tone to reflect sun light and reduce the urban “heat island” effect. It helps to cut summer-cooling costs, makes life easier on urban vegetation and improves air quality For more on the Chicago Green Alley program, see “A Pilot Project Takes Off,” in the spring issue of Sustainable Urban Redevelopment, or go online to www.SURmag.com. “There is 11-percent crumb rubber in the GTR blend, which makes up 5.5 percent of the hot mix,” Williams said. An added benefit of using the reclaimed asphalt is that it also includes asphalt cement which will reduce the amount of new asphalt cement that is needed in the new hot mix. CDOT is also giving the ground tire rubber mix a try as a cold patch to fill pot holes. “I think anywhere you are going to use an asphalt pavement product, it has a real possibility,” Williams said of the GTR rubberized asphalt. “It is showing us that it performs as well as, if not superior to, our polymer-modified asphalt cements. We don’t do a lot of parking lots, but I don’t see why you couldn’t use it there as well.” Federal Mandate: More Harm than Good? There was a push in the 1990s to encourage the use of recycled tire rubber in asphalt pavements. But the approach in some cases had mixed results and may have produced the opposite effect by giving rubberized pavements a bad name. “The Intermodal Surface Transportation Efficiency Act (ISTEA) required each state to use rubber in increasing proportions until it had 20 percent rubber usage rate. If they didn’t they would have their funding withheld,” said Doug Carlson, executive director of the Rubber Pavement Association. Perhaps to encourage innovation, the legislation did not have any specifications to follow, which complicated matters. At the time the only viable process was a wet process that involved having a special blending unit attached to the hotmix plant to agitate the liquid to keep the crumb rubber in suspension before it was mixed with the aggregate. The process was patented and tightly controlled by the holders. Very few suppliers were franchised. They were looking forward to capturing this huge national market, according to Carlson. 12 June 2008 Sustainable Land Development Today http://www.SURmag.com

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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