Turning waste into treasure, the United States has developed coal ash polyurethane composite materials

US researchers use waste coal ash to develop lightweight PU composite material.

According to North Carolina Agricultural and Technical State University's Center for Composites, the material could be stored underground for decades without harming the environment. Kunigal Shivakumar, director of the research center, said that if it is taken out and re-ground into powder, it can also be used for manufacturing.

"Coal ash is not a waste material, but a valuable resource if handled properly," he said. The mixed material can be molded into exterior trim panels, cover panels and interior moulds. "For long-term storage, it can be injection molded into large blocks," he added.

Coal ash can be used as a raw material for new materials, but remains chemically inert when mixed with polyurethane, said Wade Brown, an assistant research professor on the project who holds a partial patent on the PU process.

He added: "This is what urethane does, and soot is just the form it exists in."

The state of North Carolina provided the university with a two-year, $400,000 research grant to study the "beneficial reuse" of coal ash. In total, about 39,000 tons of coal ash were dumped into the Dan River near North Kayton in 2014.

The key to this innovation, according to Shivakumar, is that no additional heat is required for the production process and that any type of coal ash from a coal-fired plant can be directly processed. The process of removing heat reduces production costs and improves the environment, "it's a clean technology," he said. The material contains 75 percent coal ash, which could potentially increase to 80 percent. Shivakumar said the research team once placed the material in test basins for several weeks and found that it neither dissolved nor absorbed water.

The research team is actively working to develop commercially viable products from this material. According to the survey report on the production and utilization of coal combustion products affiliated to the American Coal Ash Association: In 2014, a total of 130 million tons of coal ash waste was generated in the United States.