12B-i Recycled Asphalt
Not Preferable Why is traditional Asphalt environmentally unsustainable
Asphalt pavement is commonly composed of 5 percent asphalt (a petroleum derivative) and 95 percent Coarse (stone, gravel), and Fine (sand) aggregates - laid down in layers and compacted.
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Excessive use of stone Aggregate component of Asphalt – leads to excessive mining/ quarrying which implies: • Use of water and fuel for mining (= CO2 emissions) • Quarries abruptly interrupt the continuity of open space, ruining habitats for flora and fauna alike.
Asphalt Pavements are highly recommended if the following substitutes are incorporated: 1. Aggregate Substitutes for Asphalt Pavement:* • Substitutes for Coarse Aggregate = Crushed concrete, foundry sands, hydrated coal fly ash and slag. Air cooled blast furnace slag and steel slag in particular provide good rutting resistance and superior friction properties, making it a choice aggregate for the surface course. Nonferrous Slag
• Substitutes for Fine Aggregate = Addition of about 35 volume % Coal Fly Ash to the aggregate component of hot-mix asphalt (HMA) enhances the resistance of the asphalt to cracks and potholes. This new type of hot-mix asphalt should last at least five times longer than the normal hot-mix asphalt.
Low-carbon content Fly Ash
• Stone quarrying causes air pollution, most notably dust. Scrap Rubber Tyres
• Asphalt Binder Modifier = Ground Recycled Rubber, if added to the HMA prior to mixing with the aggregates, allows it to chemically react with the mixture. Asphalt concrete pavements made with rubber modified asphalt cement tend to have less cracking, and wear better than regular pavements. They also significantly reduces traffic noise when used on carriageways.
2. Asphalt pavement could potentially be 100% recyclable and be reused as a Subgrade [See 12D] for new streets. 3. High-Albedo Coatings along with color pigments may be applied to Asphalt –to reduce Urban Heat Island Effect [See 12C]
Functional and Cost Benefits:
Recycled Asphalt Pavement www.pwri.go.jp/team/pavement/english/subject/projects.html
126 ADDITIONAL GUIDELINES
• The hydrophobic nature of fly ash gives pavements better resistance to cracking & potholes, making them safer and more durable, with a longer Pavement life. • Cost saving by decreasing the need for asphalt binder. • Less expense and frequency of required maintenance treatments to keep the pavement in good functioning condition. • Reusing materials reduces the need for mining virgin aggregate and the associated environmental impacts. (See left)
*Source and Copyright 2008: by The Industrial Resources Council Street Design Guidelines © UTTIPEC, DDA 2009 http://www.industrialresourcescouncil.org/Applications/HotMixAsphaltPavement/tabid/378/Default.aspx