By JOHN E. WEARE
On a sweltering summer day when few braved the heat (seems like a lifetime ago), I needed a photo before Friday afternoon deadline. Time was ticking away when I spied a small crew soothing a just-poured driveway. The men did not mind having their picture taken. Later, I wrote about the new cement, and construction in general, in my caption. Monday morning a helpful contractor set me straight: The material was actually concrete, which contains cement as a major dry ingredient.
Proper diction when describing building materials is not much of a worry these days. However, the “New Things Happening In Recycling” session during the recent Keep Nebraska Beautiful convention at Kearney taught me that used concrete could potentially become a more common component of new concrete.
Learning about how to recycle something beyond what falls into the dozen or so categories handled at the Keep Alliance Beautiful Recycling Center is intriguing. Sure, you can dive deep into the intricacies of cardboard or plastics, but it is good to remember how vast the industry is.
Like boxes and food containers, concrete is everywhere. I have seen local contractors and pre-mix businesses crush slabs and chunk back into aggregate. The City of Alliance has spread these man-made rocks onto our alleys as an example of reuse. Putting the aggregate back into what a cement mixer delivers is more complicated.
Christopher Exstrom, professor of chemistry at the University of Nebraska-Kearney, transported our group of Keep America Beautiful affiliates back to class. He has also worked with KNB on the School Chemical Cleanout Campaign. Exstrom said that concrete is a terrible thing to waste. There was 250-530 million tons of construction and demolition waste (EPA, 2018), of which up to 67 percent is concrete and only five percent of that is recycled. Old concrete can serve as recycled concrete aggregate (RCA), he said. “One huge consideration is how does this recycled aggregate perform versus traditional?”
One slide during the presentation detailed how University of Nebraska researchers had received a 2-year $805,000 grant ($100K to UNK) from the Department of Energy to reduce the concrete industry’s carbon footprint. At UNK their emphasis is to get the undergrads involved, Exstrom noted.
Exstrom is working with faculty and students through a grant to study recycling concrete and the rate and efficiency of CO2 reaction and how to speed up the process. “Every square inch of concrete is reacting with CO2 as we speak – it is slow,” he said. “We will study the mechanism of the process – find out how to scale it up and use as much concrete as possible.” He illustrated how the researchers utilize tools such as x-rays and a scanning electron microscope to identify crystalline materials in RCA.
On the surface, an advantage of recycled concrete would be creating aggregate from existing materials to reduce what would otherwise be dug from the ground and transported. If RCA is truly feasible, a vastly greater win could be carbon-negative concrete. As stated on one of the slides: We’re not there yet, but in the right circumstances, the production of concrete could actually store more CO2 than it releases into the atmosphere