CONSTRUCTION & DEMOLITION: Paving Asphalt's Way for Roof-to-Road

Recent technological advances have been made in recycling asphalt roofing waste, or shingles, into highway and road pavement. These include the improved ability to separate and grind shingles into paving feedstock, and the development of appropriate mix designs.

In the past, problems with asphalt roofing waste reuse have included equipment design, processing inefficiencies and a lack of feedstock continuity. In the '80s, researchers tried to burn the roofing waste to recover the energy as steam. However, equipment design and production efficiencies posed significant hurdles.

Also, recycling factory roofing scraps into new shingles proved problematic when manufacturers searched for technology that could maintain performance specifications. Now, most manufacturers find it more economically feasible to recycle scraps for basic paving and patch use.

But shingle recycling still holds promise. Today, asphalt and shingle content match chemically with the primary ingredients of hot mix asphalt. However, shingle asphalt is "harder" than paving asphalt, requiring special corrective measures in its design into hot mix asphalt.

Nevertheless, mixing shingle and paving asphalt can increase a pavement's resistance to wear and moisture, decrease rutting, and reduce both thermal and fatigue cracking.

In fact, many paving experts believe that mix designs using 5 percent recycled shingles are (by weight) suitable on interstate highways. On low-volume roads, such as driveways and industrial parking lots, 10 percent to 15 percent recycled shingles can be used.

For recyclers, the supply and demand of asphalt roof-to-road recycling promises to make shingle recycling feasible and commercially viable. In the United States, an estimated 10 million tons of asphalt roofing waste, consisting mostly of tear-off shingles containing 20 percent to 30 percent asphalt, are sent to landfills each year at a cost of more than $400 million in disposal fees. In addition, approximately 500 million tons of asphalt pavement are produced annually for roads and other paving surfaces. Consequently, recycling shingles into pavement could provide substantial benefits through reduced disposal expenses and landfill use, lower paving material costs, improved pavement performance and greater resource conservation.

As the waste and paving industries master the technical issues of roof-to-road recycling, the viability of shingle waste recovery has shifted toward economics. Profitability is expected to focus on regional tipping fees, transaction costs, transportation-drop-off synergies, economies of scale, raw asphalt pricing and efficiencies in producing clean and consistent feedstock.

Within the building community, disposal fee variables and transaction costs remain the primary barriers to voluntary waste recycling. This means that in areas with low tipping fees, shingle recycling and other construction waste recycling may not be commercially profitable unless offset by recycling yard accessibility, the development of take-back or collection programs, or mandatory recycling. However, in areas with relatively high tipping fees or strong transportation/collection synergies, the economics of asphalt roof-to-road efforts are encouraging.

As regional recyclers and pavers report success with asphalt shingle recovery, the construction industry's enthusiasm for roof-to-road programs has gained momentum. Indicative of this trend was a recent Chicago seminar, "Asphalt Shingle Summit," which focused solely on opportunities and challenges for roof-to-road recycling.

Hosted by the Construction Materials Recycling Association (CMRA) based in Lisle, Ill., the forum drew participants from a broad range of roofing, paving, construction and recycling concerns.

Participants decided to build a page on CMRA's website [www.cdrecycling. org]. Here, professionals can share and exchange technical information, research studies, discuss business concerns, post trade groups, and discover universities and governmental agencies pursuing the recovery of asphalt roofing wastes.