There are plenty of contractors who are in demolition that are rarely heard of even within the industry, because they are not involved in big, high-profile projects such as stadiums or large industrial building complexes.
Collectively, the quantity of wood, brick, mortar and concrete structures they demolish is sizeable, but not easily measurable. It would be difficult to get accurate figures on the quantities involved, because many small demolition projects such as razing a house or the concrete curbing of a couple of streets rarely are published in the local newspaper, let alone a prestigious magazine.
An estimate of the quantities of construction materials demolished could be calculated by the tons of materials recycled, but even that would be approximate and some demolition materials do not get recycled. Nevertheless, recycling construction materials from small demolition projects is big business; big enough that PMI (Patuxent Materials Inc.) has four portable crushing-screening plants in operation year ’round.
PMI’s headquarters is in Crofton, Md., with its crushing-screening recycling services extending throughout the greater Baltimore area. PMI is one of the largest concrete and asphalt materials recyclers in Maryland. Besides the company’s two materials dump centers set up for crushing and screening, the company offers contract portable crushing-screening on the project site or at the contractors’ respective waste materials yards.
PMI’s two dump centers are strategically placed with one in Crofton and one in Baltimore, about 1 mi. from the Oriole Park, home of the Baltimore Orioles baseball team. With many demolition activities going within 25 mi. of these centers, it is cost effective for the contractors to either haul the demolished construction materials themselves or utilize PMI’s hauling services.
PMI owns and operates 65 tri-axle dump trucks with 23-ton (21 t) payload capacities and two semi-trailer dump trucks with 24.5-ton (22 t) payload capacities.
PMI recently bought a stone quarry about 10 mi. north of Baltimore where it is producing stone aggregates. However, according to, Matt Andrews, crushing operations manager of the company, the company intends to make this facility the third center for receiving concrete and asphalt materials for recycling.
Some of the bigger contractors have their own dump centers where PMI brings its portable plants periodically for crushing-screening the dumped construction materials. The up side for the contractor is he has no tipping fees, as is the case if the demolished materials are taken to a PMI center. The down side is, there must be enough space in the contractor’s yard to store at least 10,000 tons (9,072 t) of concrete or asphalt.
“We cannot justify moving a crusher, a screening plant and a stacker for less than 10,000 tons to crush. And the contractor cannot justify the higher crushing costs per ton if the quantity of materials is less than the 10,000 tons,” said Andrews. He said the company has regular customers in and around Baltimore that build up enough brick, block and other concrete pieces that they have PMI crushing-screening equipment brought to their facility every 12 to 14 months.
PMI crushing equipment is set up at four to five different locations each year, besides the company’s own two crushing-screening centers. As much as 78,000 tons (70,760 t) of concrete was crushed and screened in one visit.
Cost Effective for
Most Demolition Contractors
Unless a demolition contractor has large quantities of concrete to crush and screen, the company cannot justify the investment required to purchase the portable crushing-screening equipment.
A crushing plant and a screening plant is the minimum equipment needed. Often, a hydraulic excavator also is used, to feed materials to the crusher, another hydraulic excavator is used for reducing the size of the concrete pieces and one or more front-end loaders are used to bring the unprocessed construction materials to the excavator that is used to feed the crusher.
The same loader removes and relocates the finished aggregates from the stacks created by the crushing and screening. If there are dump trucks picking up the aggregates, a loader also might be needed to load these trucks.
Besides the major investment in equipment, the contractor needs a 4- to 5-person crew for operating all the equipment efficiently. This is why the crushing-screening services rendered by PMI to the demolition contractor are so advantageous. No quantity of construction materials is too small. The demolition contractor does not have to operate a crushing-screening center and or market the aggregates. PMI takes care of this.
PMI maintains a Web site for promoting its aggregates, as well as listings in the yellow pages, and it depends on word-of-mouth.
“We make very good quality aggregates from crushed concrete. It is important to offer quality aggregates,” said Andrews.
Andrews feels that quality aggregates encourage repeat business and promote good word-of-mouth advertising for the business.
Often, demolished construction materials such as concrete contain unwanted materials such as rebar. Further, there are wood pieces mixed with concrete pieces, thus preventing the crushing-screening process from producing clean aggregates. PMI addresses both issues with success. All concrete known to contain rebar is reduced in size with a hydraulic excavator fitted with a breaker for removing the steel prior to the concrete being fed to the jaw crusher. There is an electromagnet mounted above the discharge conveyor that follows the jaw crusher for removing any residual steel that was still unknowingly embedded in the concrete. All the wood pieces are removed by hand as the concrete pieces are fed to the jaw crusher’s grizzly.
Good, Productive Equipment
PMI’s crushing-screening equipment is mostly the Extec brand; in fact, all but one crusher are Extec crushers, screens and radial stackers. The manufacturer, Extec Screens and Crushers Limited is fully owned by the Sandvik Mining and Construction Group of Sandvik AB.
PMI has several pieces of Extec crushing-screening equipment. It uses them as follows:
Besides the equipment listed in Table 1, the company owns two additional Extec S5 screens, used primarily to screen topsoil sold for landscaping purposes.
What is noteworthy about the equipment list is the company’s selection of both jaw crushers and an impactor. Andrews said he prefers the impactor for processing wash-out concrete or other non-reinforced concrete to avoid encountering any rebar or wire mesh that creates issues with the blow bars. He uses ceramic blow-bars because their usable life is in processing about 60,000 tons (544,431 t) of concrete as opposed to 22,000 tons (19,958 t) when using a high magnesium type. Another reason for having the impactor is its efficient processing of asphalt paving.
Jaw crushers are Andrews’s first choice for all other construction materials such as reinforced steel concrete and stone. While reducing the size of the concrete into 12-in. minus, using a breaker will remove 99 percent of the steel, though there is always some steel imbedded in small concrete pieces that is not noticed until the jaw crusher further reduces the piece.
PMI has its own fully trained mechanics who are capable of conducting all routine maintenance as well as the more challenging repair problems possibly experienced with the portable plants. But Andrews said there have been no major issues with any of the Extec equipment.
“This equipment has proved to be very reliable equipment and if we need any parts we receive them within a couple of days from the Extec dealer [Extec Eastern]. The dealer offers very good service and that is why we continue to buy Extec equipment from them,” said Andrews.
PMI keeps the number of aggregates offered to the marketplace to three sizes. The Extec crushing-screening systems’ throughput averages 195 tons (177 t) per hour, except when processing wash-out concrete where the finished products throughput is 235 tons (213 t) per hour. The products made are RC-6 (1.5-in. minus), RC-2 (2.5 to 1.5 in.) and RC Surge (5 to 3 in.). These are very popular sizes for site-work projects where most of the PMI aggregates end up. Crushed and screened concrete does not meet Maryland DOT specifications for road base, so most all of the aggregates are sold to contractors for private construction projects.
In a Nutshell
There are big demolition contractors who can justify the purchase of their own portable crushing-screening plant. In the long run, these contractors reduce the crushing-screening costs associated with recycling the demolished construction materials.
For all others, there are specialized crushing-screening contractors such as PMI. Choosing a crushing-screening contractor should be done carefully to be sure the contractor has the right equipment for the job and that both the contractor and the equipment are reliable.
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