For thousands of years, concrete has been one of the most widely-used building materials in the world for many reasons. It is relatively inexpensive, extremely durable, and not prone to rot, rust, or decay like wood or metal…
The history of concrete is one of innovation and resourcefulness. It was first used by the Bedouins in 6,500 B.C. and then embraced by ancient Egyptians and Romans instead of brick for its flexibility. It could be poured into forms and shaped into everything from solid flat surfaces to archways and domes.
The material entered the modern age in 1849, with the invention of reinforced concrete by French gardener Joseph Monier. The coming decades saw reinforced concrete used in the construction of many iconic structures, including the world-famous Hoover Dam between Nevada and Arizona, completed in 1936, and the Grand Coulee Dam on the Columbia River in Washington State, completed in 1942.
Asphalt is another popular building material, especially in North America. And much like concrete, asphalt’s history goes back thousands of years, with the first known use being to construct a road in Babylon in 615 BC. It was used by the ancient Greeks and Romans as a sealant for baths and aqueducts and later for caulking wooden ships. It was poured on top of stone roads in Scotland around 1803 and used to pave roads in America in the 1860s.
A few decades later, in 1901, asphalt was introduced by the H.M. Reynolds Shingle Company as an alternative to wood or slate shingles with the slogan: “The roof that stays is the roof that pays.” Despite the introduction of metal, solar, and other materials over the years, seventy percent of houses across North America still use asphalt shingles on their roofs.
Needless to say, nothing – not even the most well-built concrete structure, paved road, or asphalt-shingled roof – lasts forever. Concrete cracks and breaks, roads wear down, and asphalt shingles erode from wind, rain, snow, and blistering heat. For many years, old asphalt or concrete past its prime was often hauled by trucks to landfill sites and dumped. This was problematic for a number of reasons, from the pollution generated by dump truck emissions to taking up considerable space in dump sites.
Fortunately, there are today many initiatives aimed at reducing, reusing, and diverting concrete and asphalt waste from dump sites and giving these materials a new life, saving the environment and money in the process. Because it is often thick and heavy, concrete needs to be broken down before it can be repurposed. In cases where it is contaminated with other materials such as rebar, wood, or wire, these need to be removed as well. While softer than concrete, old asphalt also must be crushed into smaller pieces and screened for foreign materials, which can be done through mobile asphalt screening and crushing equipment to produce reclaimed asphalt pavement (RAP).
With environmental and financial forces in play, the market for RAP has grown in recent years. According to a survey of asphalt producers conducted by the National Asphalt Pavement Association (NAPA) and Federal Highway Administration (FHWA), over seventy-nine million tons of mainly reclaimed asphalt pavement and recycled asphalt roofing shingles were used to make new asphalt pavements during 2016 – the most recent year for available survey data – and the news keeps getting better. For every construction season since 2009, about 117 million tons of warm-mix asphalt (WMA) was produced in 2016.
It will come as a surprise to many that asphalt rather than glass or plastic was identified as the number one recycled product by the Environmental Protection Agency and Federal Highway Administration in a report to Congress, twenty-five years ago. According to the NAPA, “It [asphalt] continues to be reclaimed and reused at a greater rate than any other product in the U.S.
“A wide range of waste materials are now incorporated into asphalt pavements, including ground tire rubber, slags, foundry sand, glass, and even pig manure, but the most widely used are reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS). The use of recycled materials in asphalt pavements saves about fifty million cubic yards of landfill space each year.” In fact, recycling and reusing asphalt cement in RAP and RAS “saved more than $2.1 billion in 2016 compared to the use of virgin materials and saved nearly 50 million cubic yards of landfill space from reclaiming RAP alone,” says NAPA.
It is estimated that worldwide, transportation – including road construction – accounts for fourteen percent of greenhouse gas emissions, while in North America alone, this figure is closer to eighty-five percent. And in some provinces, such as British Columbia, estimates put the figure at around forty percent. Greenhouse gas emissions are an issue and contribute to global warming.
One way to lessen these emissions is to reduce the number of vehicles on the road, including dump trucks taking heavy loads of concrete and asphalt to landfill sites. Diverting these heavy loads and repurposing old broken concrete for infill or road base material means not only less waste ending up in landfills but materials being hauled shorter distances, reducing the amount of fuel used and lowering our carbon footprint.
Just as old asphalt roads and shingles can be recycled into new roads; concrete is another construction material ideal for reuse. Although it can last hundreds of years, concrete, like asphalt, is heavy, and moving concrete in trucks requires considerable fuel and manpower. According to The Cement Sustainability Initiative, a report prepared by the World Business Council for Sustainable Development, over nine hundred million tonnes of waste concrete is generated every year in the United States, Europe, and Japan, and “concrete recovery is achievable – concrete can be crushed and reused as aggregate in new projects. As part of the Cement Sustainability Initiative (CSI), the cement industry has been looking at recycling concrete as a component of better business practice for sustainable development.”
The advantages of recycled, recovered, and reused concrete are many, from lowering the use of new – virgin – aggregate to reducing transportation costs, fuel emissions, and unnecessary landfill. Waste can even be eliminated with the goal of zero landfill for concrete. This can be achieved by crushing and reusing old concrete as an aggregate or fragments for making new concrete. This will be important in coming years, particularly in the United States, as many of the roads constructed during the boom of the 1950s have outlived their lifespans and urgently need to be replaced.
Likewise, asphalt is a key component of road replacement. There are over 2.2 million miles of paved road in America, and about ninety-three percent is surfaced with asphalt. Much of it – if mixed with reclaimed asphalt pavement – will result in considerable cost savings over using new materials alone. Since the Federal Highway Administration introduced a policy in 2002 for states to use recycled asphalt and other materials when possible, there has been a significant, positive increase in asphalt recycling.
While the concrete and asphalt we use for roads and other infrastructure today may not have the longevity of roads built centuries ago due to the wear and tear of cars, trucks, and other vehicles, recycling and reusing asphalt and concrete represents a significant step towards a cleaner, greener future for the planet.