The construction industry is responsible for 75% of the consumption of earth's natural resources. Stone, sand, iron, and many other finite resources are extracted in huge quantities to supply the markets. Additionally, construction sites themselves generate enormous quantities of waste, whether through construction, demolition, or remodeling. In Brazil, for example, construction waste can represent between 50% and 70% of the total mass of municipal solid waste [1]. This waste often ends up in landfills and dumps rather than being properly disposed of, overwhelming municipal sanitation systems and creating informal disposal sites.
If more care is taken, however, this waste could have enormous potential for reuse. If given proper destinations and processed correctly, recycled materials can replace those extracted from deposits to form new building components, maintaining a quality generally comparable to traditional materials.
Recycling is the process of reusing discarded materials to reintroduce them into the production cycle. This process reduces the consumption of raw materials, decreases the total volume of waste, and can create jobs for thousands of people. To start the process, an efficient separation and collection system is essential. Although the classifications are different in every country, two major classes generally exist. The first includes concrete, ceramics, stone, and mortar, which represent most construction waste. The other class concerns wood, metal, glass, plastic, plaster, and more. Here are the most common materials to recycle and what uses they often have:
Steel
Steel can be made from the combination of iron ore and coal, which is heated in a blast furnace, or by recycling scrap, which is made in an electric furnace. The recycling of steel goes back to the Roman Empire, when soldiers collected instruments of war left in trenches to produce new weapons. In fact, steel can be endlessly transformed into new objects without loss of quality. When recycled, the consumption of electricity lowers by 80%, causing a lower environmental impact and eliminating completely the extraction of raw materials.
Rebar for reinforced concrete, wires, nails, and some metal profiles are generally made from scrap metal.
Concrete
Recycling concrete allows construction waste to be reused and construction costs to be reduced. In recycling hardened concrete, a special crusher is used and produces what is known as “recycled aggregate”. Until recently, recycled concrete was only used as a subfloor. But tests are showing that concrete aggregate can create structural elements from 30 up to 40 MPa with the right technologies. Importantly, recycled aggregates are also anywhere from ten to fifteen percent lighter per unit of volume than virgin concrete, which entails less weight per cubic meter and thus less material, transportation, and overall project costs.
Wood
Using “reclaimed wood” has become quite popular. Hardwoods can last hundreds of years, if kept properly. They can be used in large structural parts or as slats for the manufacture of other artifacts such as crates, pallets, or supports for various purposes. But even softer, cheaper woods can be recycled, especially as a raw material for the panel industry. The most common use of recycled wood today occurs with the complete grinding of wood and manufacture of MDF sheets for the production of woodwork.
Another option, if none of the above processes can be applied, is to dispose of wood waste for biomass production by burning it in industrial furnaces.
Plaster
Recycling plaster in construction is feasible, but if it is improperly disposed of, it can emit flammable and highly toxic hydrogen sulphide, contaminating the soil and groundwater. However, if suitably processed, recycled plaster retains the same physical and mechanical characteristics as conventional plaster at a relatively low cost.
EPS
Expanded polystyrene, or EPS, is a material that can be recycled as well. EPS becomes a raw material for the manufacture of new plastic products when it is crushed and compacted. It can be used for finishes or even paints.
Glass
Although glass bottles and containers are highly recyclable, the recycling of window glass faces a series of additional complications. Due to its different chemical composition and melting temperature, it cannot be recycled alongside other glass objects, including other types of window glass itself. Window glass can, however, be melted and remanufactured into fiberglass, to be incorporated into asphalt or even combined in yellow and white reflective road paints. Broken glass can be combined with concrete to create floors and granite countertops as well.
Zinc, aluminum, packaging, fabrics. These additional materials may also have reuse and recycling options. Of course, there are also substances such as asbestos, latex paint, chemical solvents, adhesives, and lead-based paint that need to be treated carefully to reduce their impact on the environment. With growing concerns about transforming the built environment to be more sustainable, thinking about the entire life cycle of a material becomes vital. In addition to reducing the chances of dumping in clandestine locations and helping to relieve pressure on landfills, recycling can lead to lower costs for both the environment and the consumer. In addition, it reduces the demand for new natural resources, reduces production and transportation costs and eliminating the need to send waste to landfills.
Notes
This article was originally published on October 8, 2019.
