DustBoss equipment controls dust on a mall demolition project in the US capital.
One of the Washington, D.C. area’s most experienced demolition contractors has successfully controlled extensive dust from taking down the old Waterside Mall, a 4-storey, heavily-reinforced concrete structure totaling 111,484 square metres. Crews were able to effectively suppress both surface dust and airborne particles with portable high-performance misting equipment, despite the crowded urban location and close proximity to the local Metro station tunnel entrance — 21 metres from the razed structure — in what has been called a “surgical” demolition project.
Engineers from Wrecking Corporation of America (Alexandria, VA) knew from the outset that the densely populated area and close proximity to remaining structures would require extraordinary precautions. “The Metro station entrance has a way of creating a vacuum,” explained executive VP Terry Anderson. “If the wind is blowing the wrong way, the dust gets sucked right down. The site was also hemmed in on three sides by structures that needed to be preserved, so we had to do a very selective removal, while protecting the entire surrounding area from the nuisance and potential hazard of airborne dust.”
After researching possible solutions, Anderson decided to rent a DustBoss DB-60. As the largest of the suppression designs from Dust Control Technology, the unit atomizes water droplets to the optimum size for particle capture, launching them 60 metres or more with a powerful 18 kW fan that generates nearly 850 cubic metres per minute. With its built-in oscillation, the DB-60 can effectively cover nearly 0.2 hectares with a fine, dust-trapping mist.
The DB-60 is a fully automatic ducted fan design, mounted on a wheeled carriage so it can be easily located to accommodate wind direction or specific work areas. The unit delivers adjustable elevation from 0-50 and a 40 degree oscillation range, providing WCA crews with outstanding coverage.
“The droplet size is critical to effective suppression,” explained Dust Control Technology CEO Edwin Peterson. “Dust particles tend to be in a fairly narrow size range, so the water should be atomized to droplets near that same size for maximum attraction. Our standard models produce droplets from 50-200 microns, but all of our units are designed to be easily customized for targeting specific particle sizes or for cooling applications,” he said. Peterson observed that the nozzles, fan and other components must also be designed to work together for optimum flow, spray angle and delivery pressure to achieve the necessary droplet size, velocity and distribution.
Anderson’s crews run the DB-60 with power from a portable generator and water supplied by a fire hose. A 7.5 kW booster pump elevates water pressure in the DB-60 as high as 200 psi for outstanding particle suppression. It can also be outfitted with a dosing pump to accurately meter odor control additives or surfactants to further enhance binding of dust particles.
WCA began the project in November of 2007, and the old structure did not go easily. “This was one of the more difficult buildings we’ve taken down in some time,” Anderson admitted. He has no explanation for why a decades-old mall was built with 20-inch (51 cm) floor slabs, when the standard is about 23 cm. “We had to fight down every step,” he said. It’s also the largest contiguous building that the company has ever removed.
In addition to the crowded urban environment, the project was complicated by structures that had to be preserved, including a deli attached to the nearby grocery store. Unfortunately, sections of the structure to be demolished were directly on top of it. “We saw cut through the 20-inch slabs of concrete,” Anderson continued. “Then we had to carefully remove all debris, while protecting the integrity of the buildings to remain and controlling the large amounts of dust that were generated by all those activities.”
WCA employed a high-reach excavator for the general demolition work, a 45,359-kg Komatsu PC400 with a 26 metre boom. Kinshofer dedicated shears with 360 degree rotation were used for cutting the extensive amount of reinforcing steel, more than 5,000 tons overall.
Anderson’s crews also made extensive use of a 90-ton truck crane and wrecking ball. “It’s a technology that virtually never breaks down,” he said. “And it leaves a small carbon footprint.” WCA also used a 63,503 kg Caterpillar 365 track-mounted excavator to take down the structures, along with three Hitachi 450 excavators with bucket attachments and four Hitachi 330 excavators with a variety of attachments that included concrete pulverizers and demolition hammers.
WCA performed all concrete crushing and recycling on-site, with an Extec C10 crusher used to process approximately 53,519 cubic metres of material. The crushed product was used for non-structural fill and backfilling.
“By nature, concrete work generates a lot of dust,” Anderson concluded. “We felt we had to take strong measures for control on this project. The DustBoss did such a good job that we decided to purchase the unit,” he added.
