Contractors pressed to lower carbon footprint of concrete and asphalt

It is being described as the first national carbon standard for concrete.

In late March, the General Services Administration (GSA) imposed new limits on high carbon-emitting materials in major, federal construction projects. The new policy will require contractors to show the total greenhouse gas (GHG) emissions of their concrete products are 20 percent lower than limits recommended by the New Buildings Institute. The policy also requires contractors to employ several environmentally preferable techniques to lower the carbon footprint of asphalt.

“This is a very new standard and, as of now, there is very little insight into exactly what will be required by subcontractors. However, the primary requirement will be carbon capture technology,” said Ted Bowes, President of Excell Concrete Construction.

Ready-mix suppliers, Bowes said, may increasingly need to use technologies such as CarbonCure – a process of injecting captured carbon dioxide into concrete during the mixing process. The added carbon dioxide both reduces the carbon footprint of the concrete and improves its compressive strength, according to CarbonCure. At least one local institution has added carbon capture requirements to its concrete procurements, Bowes said, and several local ready-mix suppliers have installed the technology.

Other carbon-reducing products are becoming part of projects.

Last summer, Belfast Valley Contractors poured 7,000 cubic yards of ECOPact at Georgetown University’s new 12-story residence on H Street. ECOPact’s embodied carbon is 40 percent lower than standard, Portland cement-based concrete.

“In addition to ECOPact, which we are seeing more of, there is a growing push to use Portland Limestone Cement (PLC) as a replacement for Type 1 and Type 2 cement that is commonly found in concrete,” said TJ Goloboski, CEO of Belfast Valley Contractors.

PLC increases the percentage of limestone in cement to 15 percent versus the five percent used in Portland cement, and meets the same performance specifications.

“I have seen some research that says if we were to replace all Type 1 and Type 2 cement in the U.S. with PLC, it would be approximately the equivalent of taking 1.75 million cars off the road,” Goloboski said.

The industry, however, still faces challenges in providing sustainable concrete. Lower carbon products still carry a price premium.

In addition, “the carbon capture application doesn’t work in superstructures, such as tunnel mixes or bridge mixes,” said William Dennison Jr., Construction Materials Department Manager for ECS Mid-Atlantic. “Those superstructures are looking for early strength and they use pretty high cementitious factors to get those high strengths for bridges to last. If you put carbon in them, they don’t get that strength as fast.”

Industry leaders, however, are pursuing other options to lower the carbon footprint of bridge and tunnel projects, such as using higher percentages of fly ash or slag in mixes or using carbon rods rather than steel for some supports, Dennison said.

Similarly, asphalt professionals are actively researching and implementing new processes to lower the environmental impact of their products.

“The reality is the asphalt industry has been pretty green for some time because of the use of recycled products in our mix – on average 25 percent of recycled asphalt paving or RAP,” said Bill Poole, Executive Vice President and General Manager of the Asphalt Division and Demolition at Gray & Son.

Gray & Son personnel serve on several National Asphalt Paving Association subcommittees which are investigating other sustainable processes, such as warm-mix technology.

“It is essentially an additive that allows you to make asphalt at lower temperatures which reduces the amount of fuel you use,” Poole said. “We have found it also allows you to put in higher levels of recycled materials – another 5 to 7 percent – so you get a double benefit.”

The industry has identified used roofing shingles as an excellent material to include in asphalt production.

“By weight, a ton of shingle has between 16 and 23 percent liquid asphalt, whereas a ton of RAP has between 5.5 and 6.2 percent,” Poole said. “A really good way to keep shingles from going into landfills is grinding them up and putting them into blacktop.”

However, not every proposed sustainable practice — including some on the GSA’s list of preferred practices, such as recycling used plastics and rubber in asphalt mixes — has proven entirely successful. Adding recycled rubber and plastic to mixes is helpful in creating certain specialty products, such as surfaces for running tracks and other athletic facilities.

“But there has been a lot of failures in utilizing rubber and plastic,” Poole said. The process of including rubber and plastic in asphalt mix generates “blue smoke that goes into your baghouse to prevent emissions. That can do real damage. You have to be really careful or you could end up spending $50,000 to replace the bags in your baghouse.”