How to properly prep recycled construction materials

The benefits of recycled construction materials such as concrete and asphalt can be plentiful.

Recycling these materials is less expensive than virgin material, reduces the amount of material that ends up in a landfill and means less mining for producers and contractors.

While beneficial, processing recycled materials comes with its fair share of challenges. Since the material in question was previously used in roadways, parking lots, driveways, walking paths and other surfaces, it is often full of rebar, teeth from road milling machines and other objects that can be detrimental to crushers.

To help avoid equipment damage and downtime, Superior Industries’ Jeff Gray says producers and contractors should take the time to prep recycled materials, removing objects before crushing.

“Every hour you spend processing exponentially pays off on the finished product rate that you get compared to if you don’t process the raw piles and you have a lot of expensive equipment running at maybe 25 percent of its capacity,” says Gray, director of international sales and mining at Superior.

“Controlling the size of the individual particles, removing large pieces of rebar and mesh – or clipping them into smaller sizes so they can be removed by the processing plant magnets – is huge. It all comes down to equipment utilization.”

This prep work can be done before the first crush with tools such as hydraulic hammers, crunchers, pulverizers and boom magnets. After the first crush, operators should rely on a self-cleaning magnet to pull pieces out. A magnet can be used again after the second crush, if applicable, to further clean the material.

Pieces of steel or other large or sharp metal objects getting through to crushers and other pieces of equipment can lead to increased “black belt time” – time when material is not being processed – Gray says.

“If a small piece of steel gets hung up in the chute and cuts the conveyor belt, you could be looking at two to four hours of downtime in one day,” he says. “Maybe that could have been avoided if you had a shear on your raw pile just sorting through the feed to the plants and eliminating anything longer than 2 or 3 ft. from the feed. You’ll never get it 100 percent [clean], but that’s the trade-off – the money you spend prepping the raw pile versus uptime on the crushing and screening plant.”

Higher volume producers have, in large part, figured out that line between prep time and uptime, Gray adds. In some cases, he says those producers are seeing times similar to that of a virgin aggregate producer.

Sometimes, though, producers will increase their equipment sizes and skip the material prep before crushing it.

“In some cases, they may only be processing a 10,000- or 20,000-ton pile of material with a portable spread,” Gray says. “They move in, do it and move out. They may not spend the extra money for the equipment needed to prep the raw pile, so they just have to deal with what’s in the pile and maybe oversize some of the equipment to handle it.”

Recycling’s future

The emphasis on recycled materials’ environmental benefits – such as reduced carbon output – is something Gray is already seeing. He anticipates the onus on incorporating more recycled materials into construction projects will continue to grow.

Larger metro areas are currently leading the charge.

“The Dallas-Fort Worth area and other big cities have requirements on some road projects to either use the recycled materials in place without hauling them away from the construction sites, or just require a percentage of the new materials be recycled,” Gray says. “The West Coast – California, namely – leads the push on the use of recycled materials. It comes down to municipal state work and commercial work and their flexibility.”

Something delaying that growth into lesser populated areas, Gray says, is the financial barrier to entry.

“One of the challenges to expanding the use of materials like asphalt and concrete is the availability and the cost to process it,” he says. “In a smaller region with lower volumes, you can’t afford to own a plant to process materials – say you only generate 50,000 tons a year whether its recycled concrete or asphalt – so you have to hire a subcontractor to come in and process it.

“In larger cities and metropolitan areas, there are typically multiple operations where people can haul their waste and set up a stationary plant that can process,” Gray adds. “Sometimes it’s the cost situation that limits its expansion into smaller populated areas.”

One key to increase the amount of recycled materials that can be used in construction will be producers advocating for their own mix designs.

“It takes the people that actually make the asphalt to promote that acceptability, do the testing and develop the case studies,” Gray says. “That’s what we see pushing it – the actual producers doing the testing on their own and proving to the states that it works, has longevity and is not a lesser product.”

Related: Superior Industries to acquire New Mexico crushing manufacturer