What happens to a building’s material after demolition?
Your guess is as good as mine – some are recycled, while others go into landfills.
However, landfill rules are becoming tighter worldwide to discourage the disposal of materials via that route and encourage recycling and other options with less environmental impact.
Recycled materials reduce the impact of building projects on the environment while promoting cost savings.
Steel is the most recycled building material. Ninety-three percent of the steel used in the construction industry is recycled because it facilitates cost savings for construction companies. Recycling steel also conserves the environment by diverting steel from landfills to other projects.
In the rest of this article, I’ll discuss the most recycled building materials and the key facts you need to know. I’ll also discuss how these materials are collected and recycled.
Let’s get started!
Recycled Materials in the U.S. By Type of Building
It’s crucial to understand the recycling market in the United States before proceeding to specific recycled building materials.
Construction and demolition (C&D) account for almost a quarter of the waste stream in the U.S. Such an enormous amount of waste puts pressure on the environment, especially the impacts caused by landfills.
Besides the C&D materials, plastics, glass, and compost contribute immensely to this country’s waste. Consequently, recycling was born out of the need to manage these major wastes, reduce their environmental pressure, and produce less waste overall.
Here is a screenshot illustrating the recycling market in the United States:
The U.S. recycling market by type of building. Source: Statista
According to the above chart, metal contributes the most to the recycling industry.
The other side of that coin is that products using metals make up a very high proportion of recycled building materials, as you’ll see in the next section.
The construction industry accounts for more than 50 percent of the global steel demand, thanks to its high tensile strength.
The huge reliance of the building industry on steel makes it a significant source of construction and demolition waste. The EPA states that ferrous metals like steel make up the largest percentage of municipal solid waste.
What would happen if the high amount of scrap steel from the construction industry is not recycled?
As you might imagine – it’ll end up in landfill sites, removing value from the economy and creating environmental pollution.
The recovery of this value, held in waste steel products, drives the recovery of this type of construction waste. 60% of steel is recycled globally for construction and other projects.
The 60% of recycled steel translates to 630 million tonnes of steel scrap recycled annually. Recycling saves approximately 950 million tonnes of carbon dioxide emissions.
China has the highest steel production and, consequently, the highest recycling tonnages.
For instance, in 2020, China produced 1,052 million tonnes of steel. The country’s steel scrap consumption reached 220 million metric tonnes in the same year.
The table below compares steel production and scrap consumption from recycling among the leading economies in millions of metric tonnes:
|Country||Steel Production (Mt/y)||Scrap Consumption (Mt/y)|
Table 1: Steel production and scrap consumption. Source: Statista
Recycling steel involves collecting, sorting, shredding, smelting, and purifying to obtain usable steel products.
It’s worth mentioning that due to the inherent value of steel, its recycling process differs from other recycled building materials.
Usually, most recycled building materials are sent to a landfill, or a traditional recycling center – this is not the case with steel.
Steel destined for recycling is sold to a scrap yard for processing and is resold to steel production companies. This process gives the steel a second life as it’s recycled into usable construction products.
Steel scrap sold to scrap yards comes from the following sources:
- Home scrap: This is in-house steel from steel mills. This steel is a result of steel production processes like trimming and sorting.
- Industrial scrap: This comes from steel construction materials like those used in industrial buildings and bridges. It also accounts for steel rejects from the automotive industry.
- Municipal scrap: It’s collected at the end of a building’s lifecycle or after a renovation project.
- Obsolete scrap: It stems from the rest of steel waste from household appliances and farming equipment.
After collecting scrap steel from the above sources, the scrappers take it through the sorting process before sending it to foundries or steel mills.
The sorting process begins once a sufficient amount of scrap steel is collected. Here, the scrap steel goes through a Materials Recovery Facility (MRF).
A high-powered magnet in the MRF’s conveyor belt helps segregate the steel from other scrap materials.
Once the process is completed, the scrappers send the sorted steel to foundries or steel mills for processing.
After sorting, the scrap steel is shredded into small pieces using special shredders.
The shredded steel is then sold as ferrous scrap or baled for processing in a foundry. If baled for further processing, the shredded pieces undergo fine smelting for use in other projects.
The smelting process further breaks down the ferrous scrap into small pieces. The process occurs in a steel-making furnace with temperatures close to 3,000°C.
The melted scrap steel is then poured into molds to form billets – a semi-finished product.
The billet is then processed further until it becomes the desired construction material.
If you’re looking to reduce your project’s energy consumption, check out this article on carbon footprints of building materials.
Aluminum is another popular recycled building material. Like steel, aluminum is popular in the construction industry for the following reasons:
- High strength
- Corrosion resistant
The above characteristics make aluminum suitable for construction, and it is the popularity of aluminum in construction that accounts for the enormous amounts of aluminum C&D waste generated by the industry.
Luckily, aluminum can be infinitely recycled without diminishing its quality.
For instance, according to the International aluminium Organization, 75 percent of the ever-manufactured aluminum is still in use due to recycling.
More than 30 million tonnes of aluminum scrap are recycled each year globally. The strange fact is that 90 percent of this recycled aluminum comes from construction projects.
Europe has the highest Recycling Efficiency Rate (RER) for aluminum at 81 percent.
However, China produces and consumes 10,000 million tonnes of scrap aluminum, making it the highest globally. This amount is approximately 1/3 of the world’s scrap aluminum production.
Finally, North America has the highest Recycling Input Rate for aluminum at 57%. This means that 57% of the aluminum produced in North America comes from scrap.
Aluminum is recycled in two main categories: aluminum cans and aluminum alloys.
Aluminum cans are usually recycled in a single-stream process, while aluminum alloys are recycled via shredding and melting processes.
Like steel, aluminum scrap is collected from the sources mentioned above before sorting and shredding.
Here are the key steps in the process of aluminum collection and recycling:
Collection is the first stage of aluminum recycling. Scrappers collect used aluminum materials from construction sites and homes.
In most instances, the following reclaimed materials are collected:
- Aluminum beverage cans.
- Aluminum window frames and siding.
- Doors and door frames.
- Fencing wires.
During the scrap metal collection process, the metal waste comes with different metals and debris from the construction project.
Therefore, sorting is necessary for recycling purposes to get pure aluminum for processing.
The sorting process sorts aluminum materials into various categories. This allows for the most efficient way of collecting and recycling each material.
The process begins by separating the different types of aluminum, such as cans, window frames, and fencing wires.
After sorting, the materials are cleaned and compressed into bales.
After sorting, the aluminum scrap bales are passed through a shredder to break them down into smaller pieces.
Shredding is necessary to facilitate the loosening of paints and coatings from the bales. The paint and coating may contain hazardous materials that should not be reused.
Moreover, shredding makes it easier to melt the aluminum since it reduces the scrap’s size.
Aluminum scrap is never taken into the furnace with the coating. The coating may contain hazardous materials, and it can also reduce the melting point of the aluminum scrap.
Therefore, de-coating is necessary to remove the coat. De-coating removes oils and paints from the aluminum using an alkaline solution bath or an acid dip.
Alternatively, a specialized de-coater blows hot air into the shredded aluminum pieces. The hot air vaporizes the oils and paint from the aluminum.
The de-coating process happens before melting to ensure that only pure aluminum goes into the furnace for recycling.
The melting process converts the shredded aluminum bales into ingots or billets.
Unlike steel, aluminum melting occurs in a furnace heated at 700°C due to its chemical makeup that allows it to transfer heat efficiently.
During the process, special chemicals are added to the molten metal to separate any impurities. The chemical reaction that occurs pushes the impurities to the top for scraping.
The melted aluminum is transferred into a holding furnace called a ladle. The aluminum is then poured into ingot molds and cooled.
The formed ingots are used to create new aluminum products. These products may include electronics, window frames, and automotive parts.
In the case of billets, the molten aluminum is cooled and shaped into a semi-finished product. Billets are used for extrusion, forging, and rolling processes as follows:
- Extrusion: The billets are heated to 500 degrees Celsius before being pushed through dies with shapes that fit the intended application. The extrusion process creates parts that have consistent shapes and sizes.
- Roll forging: The billet is heated to 500 degrees Celsius for forging. During the process, shapes are created by metalworking tools that bend or cut the material into desired shapes.
Besides relying on recycled building materials, constructing modular homes is an excellent way to minimize pollution.
Copper is another popular recycled building material.
Copper is a common material in construction projects due to its high resistance to corrosion, hail, fire, and mildew.
It is also an excellent conductor of electricity, making it the go-to choices for electrical wiring.
The common parts of a building where copper is used include:
- Rain gutters
- Roofing systems
- Flashings and copings
- Wall cladding
- Electrical wiring
Due to its high applicability in construction, copper also accounts for large amounts of C&D. As a result, many countries turn to copper recycling to reduce their environmental impact.
Europe leads the world in terms of copper recycling. 41% of Europe’s copper demand is sourced through recycling.
Urban mining (recovery of end-of-life products) is Europe’s leading source of copper scrap for recycling.
The end-of-life products contributing immensely to copper scrap include automobiles, wires and cables, electrical equipment, and construction parts like plumbing fixtures.
Copper also accounts for large amounts of C&D waste in the U.S. However, the U.S. has a lower recycling rate for copper than Europe and other major economies.
In 2018, the US recycled 870,000 metric tonnes of copper, a one percent increase from the previous year.
The U.S.’s recycled copper accounted for 34 percent of the country’s refined copper needs.
Overall, 8.7 million tonnes of copper are sourced from recycling end-of-life products.
Direct copper scrap use has been on the rise globally since 2011. This is attributed to the increased availability of copper scrap on the market due to recycling initiatives.
The high demand for copper in electronics and electrical applications is expected to fuel the growth of direct copper scrap use in the coming years.
Here is a table demonstrating the growing demand for direct copper scrap use by manufacturers from 2011 to 2021:
|Year||Use in Thousand Metric Tons|
Table 2: Direct copper scrap use by manufacturers. Source: Statista
As with steel and aluminum, collection is the first step in copper recycling. Copper scrappers collect copper scraps from construction sites in the form of:
After piling sufficient copper scraps, the scrappers transport them to the recycling center for processing.
At the recycling center, copper goes through the sorting and separation process.
Sorting involves removing unwanted materials such as insulation, plastic, or other metals from the copper scrap.
Separating involves categorizing the copper scrap into different grades depending on its alloy content and purity. You should note that copper comes in different grades that must be separated before recycling. These copper grades include:
- #1 Copper: It’s the purest grade and contains 99% copper. It’s free of insulation, oil, or oxidation. As a result, it’s also the most expensive copper grade.
- #2 Copper: It’s the copper grade below level 1 and has imperfections such as paint, oxidation, and insulation. Due to the many filtration processes required, these imperfections may make cleaning and recycling this copper grade challenging. A good example of this grade of copper is oxidized copper pipes.
- #3 Copper: It’s the lowest grade that has many impurities. Roofing copper is an excellent example since it goes through a tremendous beating in its lifetime. It’s also exposed to excessive dirt and grime. Consequently, it’s the cheapest copper grade you’ll ever come across.
Here is a video demonstrating the difference between type one and type two copper:
The sorting and separation processes are done manually or with automated machines. Although the manual method is cheaper, it takes longer than automated machines.
After sorting and separating, the copper scraps go through the shredding process. Here, the copper scrap is shredded into small particles to remove any remaining insulation.
Shredding also aids in the removal of any impurities that may be present. Lead and tin are the most common impurities at this stage.
Grueling involves passing the copper through a screener to identify its quality. The quality is determined by the copper’s alloy content and purity.
After the grueling process, the copper is passed through a density separator to separate it based on density.
The separated copper scraps are loaded into a furnace for melting at 1,084°C.
During the melting process, copper is cast into the required shape and left to cool. After cooling, it’s remodeled into rods, sheets, and wires that can be used in new construction projects.
The recycling of building materials is a booming industry worldwide as countries seek to lower their carbon emissions, energy, and natural resource utilization.
Steel, aluminum, and copper are the most recycled building materials globally due to their prevalence in construction and ability to be formed into recycled products.
Besides conserving non-renewable, virgin resources, using these recycled materials helps to reduce the cost of a building project by substituting cheaper recycled construction materials for new materials.
Now that you know the most recycled building materials, check out these sustainable building materials changing the market.