The NDA holds the belief that demolition debris is indeed more benign than construction waste, and should be isolated from studies that group both types of debris together. Since environmental remediation companies are by law called in to remove all hazardous materials (i.e., asbestos) before demolition begins, what remains is material that was no more dangerous than what had been in the building for many years.
The evaluation the NDA commissioned - developed by the solid waste management consulting firm Gershman, Brickner & Bratton Inc. - surveyed all of the association's regular U.S. membership. The survey response was a healthy 20%, well above the national average.
The findings indicated that demolition providers reuse or recycle approximately 75% of the more than 115 million tons of demolition materials estimated to be generated annually. Many of the contractors routinely recycle over 90% of their debris.
The top reasons demolition companies cited for performing a high percentage of recycling are:
- it is required by law and specifically required in many demolition contracts;
- and there are now more readily available markets for the recyclables found within the C&D waste stream.
The survey found that California is the state with the greatest amount of demolition debris recycling. Other top states include Florida and New Jersey. Also reporting a lesser but still significant amount of recycling are Texas, Minnesota, Washington and Illinois.
Materials at the top of the list of recycled demolition debris include, in order of magnitude: concrete, asphalt pavement, metals, bricks/blocks and wood.
The NDA heartily supports the move toward the recycling and reuse of as much demolition debris as is economically feasible. Finding profitable aftermarkets for recycled materials is an ongoing issue. Until then, the organization encourages local, state and national legislative bodies to gain a full understanding of the economic realities of today's recycling industry based on a scientific study of the real facts. ?
Michael R. Taylor, CAE, is executive director of the National Demolition Association. For more information, visit www.demolitionassociation.com or call (800) 541-2412.
Contractor Achieves 100% Recycling Rate
Costello Dismantling Co., Inc., Middleboro, MA, was contracted by Turner Construction Co. to dismantle a pedestrian bridge over Western Avenue as part of a major expansion project for Harvard University. The bridge was located in the Allston section of Boston between two former WGBH TV and radio buildings. The main bridge beams were prestressed concrete spanning 75 ft. over the busy thoroughfare. The connectors, from concrete piers to their respective buildings, spanned 15 ft. each and were also constructed of prestressed concrete. The entire bridge was covered with an extruded aluminum and glass weather cover.
There were many urgent factors that shaped the design of the demolition and safety plan that was implemented for this project. Obviously, a street closure in a busy urban area requires that work be completed as quickly as possible. Protection of all adjacent property is imperative, including the street and sidewalks, the connecting buildings and an active 13.8-kV transformer and switch gear very close to one end of the bridge. Demolition of the 5-ft.-deep concrete girders comprising the middle spans of the bridge needed to be engineered in such a way to avoid uncontrolled collapse of the girders.
Demolition began at 7:00 a.m. on Saturday, July 7, 2007. Limited space on the project necessitated the use of two excavators equipped with multiple attachments to provide multi-tasking capabilities. The 100,000-lb.-class Volvo EC460C L was equipped with a Genesis GDP 900 DemoPro for shearing, concrete cracking and concrete pulverizing; a Genesis grapple for material sorting and loading; a Lemac bucket for processed concrete loading and foundation excavation; and a 10,000-ft.-lb. Socomec hydraulic hammer for demolition of piers and foundations. The 42,000-lb.-class Komatsu PC228USLC zero tailswing excavator allowed easy access to tight areas, and was equipped with a JRB JCYC17 rotating concrete cracker, a NYE concrete pulverizer, a 5,000-ft.-lb. Kent hydraulic hammer, a LaBounty grapple and a Lemac bucket. Also on site for material handling, loading and clean-up was a Volvo L150 loader with 8-ft. forks and bucket, as well as a John Deere 317 skid steer with bucket, grapple and sweeper attachments.
A sand bed and 1-in. steel plates protected the street and sidewalks from falling debris. An engineered shoring tower was required to be placed mid-span in the girders during a carefully sequenced demolition plan.
After removal of the bridge's weather cover, the concrete demolition sequence began. The Volvo excavator with the GDP 900 DemoPro, along with the Komatsu excavator equipped with the 5,000-ft.-lb. hammer, carefully "nibbled" the girders from the top flange toward the bottom. The concern was that a sudden cutting of pre-tensioned tendons in the concrete girders would cause catastrophic failure. Instead, operators applied just enough pressure to break the concrete away from the reinforcing tendons, allowing the girder to gently sag and rest on the pre-installed shoring towers. Once the bottom flange of the girders was resting on the shoring towers, pulverizing of the concrete beams continued.
By 8:45 p.m., traffic was again flowing. At the end of the day, 8.5 tons of steel and 4 tons of aluminum were delivered for sorting, preparation and recycling. A total of 100 tons of concrete was delivered to Costello Dismantling's licensed concrete recycling facility. The glass enclosure of the walkways was incorporated with the concrete to make a recycled aggregate product.
The project design from conception to clean-up focused on a process that produced clean, segregated, easily handled and recyclable byproducts. Consequently, 100% of the Western Avenue Bridge will be recycled for future beneficial use.