Scientists are reporting a new way to repair roads by using grit, a remnant of wastewater treatment.
Grit is usually disposed in landfills. The researchers will present their results at the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo, according to Phys.org.
"We had an idea to divert wastewater grit from landfills and turn it into a marketable product," said Zhongzhe Liu, Ph.D., who is presenting the work. "We formulated it into a ceramic mortar that could be used as a patch for pothole repair."
The substance is known as grit assisted patch (GAP). GAP is ultimately safer for the environment than hydrocarbon-based asphalt, according to researchers.
The grit requires processing to become GAP, however. Wastewater containing sewage, food scraps and other waste is first processed at treatment plants. Grit contains pathogens and impurities which make it unsuitable for direct recycling.
To turn this into an eco-friendly solution, Liu and his collaborators decided to incorporate grit into a chemically bonded phosphate ceramic (CBPC), which are used to treat hazardous or radioactive waste for disposal.
“In the first step of making a CBPC, we mix the wet grit with calcium oxide and magnesium oxide, which form an alkaline grit slurry that prevents the proliferation of pathogens," said Liu. "The second step is to add a weak acid, potassium dihydrogen phosphate, into the pathogen-minimized alkaline slurry to form the grit-CBPC mortar."
After analyzing GAP performance in the lab, researchers found it has a compressive strength that is comparable to asphalt pavement. The group has filed a patent for GAP, reported Phys.org. The group is also working on improving GAP's compressive strength even further so it could potentially be used for other applications, including building wheel stops at the end of parking spots.