Along with longer daylight hours, outdoor barbecues and daily trips to the pool, the summer brings an increase in construction jobs, particularly home construction. One new trend in house construction/demolition is a method called deconstruction. This process involves taking down blighted homes piece by piece, essentially building the house backwards. This method allows more products to be recycled and diverts the reusable materials from ending up in the landfill.
Deconstruction projects have already been put into action in several major Midwestern cities, including Milwaukee, Chicago, Cleveland, Pittsburgh and Detroit. Workers deconstructing several homes in a floodplain area of Milwaukee were able to salvage 95% of the material, with 85% recycled, 10% able to be reused immediately and only 5% sent to a landfill. A pilot deconstruction project in Detroit saved 75% of the material for immediate reuse, sent 15% to be processed for recycling, with only 10% being landfilled. The average expected costs of deconstruction projects is around $16,000 with projected profits from selling salvaged material averaging around $24,000 per home.
From bricks to lumber to concrete, a variety or the materials can be reused. One example of how the materials can be reused immediately is lumber previously used to hold up the home recreated into tables, planks and cabinet doors. However, a majority of the material must first be reprocessed before being reused in a different form. This includes grinding up bricks and concrete to form new aggregate and filler, chipping wood down to be reused as mulch and erosion control and shredding asphalt shingles to be reused as hot-mix asphalt and pavement.
Runoff slabs of concrete can be crushed down and used as erosion control, landscaping stone or mulch and retaining walls. If ground down small enough, it can be reused as the base layer to gravel roads or construction projects, or as the dry aggregate to create new concrete. Recycled wood is used for anything from shoreline erosion prevention products to fish and bird habitats to reusable mulch for trails, landscape, gardening and playgrounds.
Hot-mix asphalt (HMA) is currently the largest market for recycled asphalt shingles (RAS). Using recycled asphalt reduces the demand for virgin asphalt cement and aggregate, which economically benefits HMA producers. The fibers from the felts and fiberglass found in shingles give cold patches made from RAS a longer life compared to those made of other materials. Recycled shingles that are ground into gravel and used to cover unpaved roads have been proven to minimize dust, reduce the amount of gravel lost into side ditches and reduce vehicle noise on these roads. These roads also tend to have a longer life and require less maintenance.
The primary reprocessing machine used in construction and demolition reprocessing is a grinder. Grinders use abrasion and compression to pulverize materials to a reduced size, using a series of wheels, drums and plates to process the material. Material is passed through a wide feed hopper, falling into the grinding chamber. Often, grinders use a hammermill in the grinding chamber to process the material. In this case, the grinding chamber contains a rotating hammer rotor with swinging hammers that crush the shingles and drive them through a screen, thus using impact grinding to reduce the material into smaller scraps. Some grinders come equipped with a grapple for easy loading, if not some form of loader is often used in the shingle recycling process to transfer the shingles from the fill pile into the grinder. Grinders are available in high or low speed models.
One unique grinder specializing in construction/demolition and wood waste recycling is the Portec Tumble Grinder. Prior to grinding, the material is passed through a 200 square foot screening area to remove rocks, dirt, sand and other contaminants. The tumble tub is a screened cylinder inclined at a 30 degree angle. The cylinder rotates at the debris is passed through, knocking dirt and rocks loose and dropping them out through the screen openings, while the large wood pieces are maintained in the screen and passed into the grinder. Removing the abrasive material such as soil, gravel and metal fragments prior to grinding allows the wood waste material to be efficiently shredded without effecting performance or damaging the grinding mechanisms. Traditional grinders do not have this pre-screening chamber, so often times this material wears down the grinding hammers, drastically reducing the equipment’s lifespan and production efficiency.
From the tumbler, the material is passed into the grinding chamber to be reduced to smaller shreds and then ejected on one of the machines two different discharge conveyors, one for the screened product and one for the ground product. This leaves the material ready to be reused rather than landfilled unnecessarily, making home deconstruction both environmentally friendly and economically viable demolition technique.