New “shield-like” coatings made from fly ash could provide a cheap, durable solution to protecting rebar from corrosion and repairing the nation’s crumbling bridges and roads, scientists are reporting.
Coatings made from some of the millions of tons of ash left over each year from burning coal could extend the life of those structures by decades and save billions of dollars in taxpayer money, scientists reported this week at the 241st National Meeting & Exposition of the American Chemical Society in Anaheim, CA.
ACS is the world’s largest scientific society and a global leader in chemistry research.
Extreme Durability, Low Cost
New coating material made from fly ash is hundreds of times more durable than existing coatings and costs only half as much, said the academic-industry research team, led by Charles Carraher, Ph.D., of the Department of Chemistry and Biochemistry at Florida Atlantic University.
The project also involves Blue World Crete Holdings of Pompano Beach, FL, and two engineering researchers at FAU.
More than 450 coal-burning electric power plants in the United States produce about 130 million tons of fly ash each year, creating “enormous waste disposal problems,” said Carraher. Almost 70 percent of the waste ends up in landfills every year, he said.
“Our research indicates that this waste could become a valuable resource as a shield-like coating to keep concrete from deteriorating and crumbling as it ages,” said Carraher.
Edbrown05 / Wiki Commons
| Almost 70 percent of fly ash is currently landfilled.|
Carraher said the new material could be used to coat and protect steel reinforcing bar (“rebar”) from corrosion and is suitable for repairing damaged concrete.
Classifications and Specifications
Laboratory tests have shown that the coating has excellent strength and durability when exposed to heat, cold, rain and other simulated environmental conditions harsher than any that would occur in the real world, Carraher said.
For example, he said, the coating protected concrete from deterioration amid exposure to air pollution acids that were 100,000 times more concentrated than typical outdoor levels in the environment.
The coated concrete remained strong and intact for more than a year of observation, while ordinary concrete often began to crumble within days, he said.
Carraher cited U.S. Environmental Protection Agency estimates that it will cost up to $1.3 trillion to repair, restore and replace concrete in domestic wastewater and drinking water systems. He also noted accounts that say this work must be completed by 2020 to avoid environmental and public health crises. Crumbling concrete roads and bridges will require hundreds of billions more.
The coating could extend the lifespan of those structures with enormous savings, while helping to solve the fly ash disposal problem, Carraher said.
Fly Ash in Concrete
Fly ash has been used in concrete in the United States since the early 1930s and hit its stride in 1948, when the U.S. Bureau of Reclamation used 120,000 metric tons of it in constructing the Hungry Horse Dam in Montana. The fly-ash mixture replaced about 35 percent of the Portland Cement in the project, although it “constituted a health hazard in the mixing plant because of the constant presence of dust in the air,” the Bureau of Reclamation later reported.
US Department of the Interior
| The Bureau of Reclamation replaced 35 percent of the Portland Cement in the Hungry Horse Dam with a fly ash mixture in the 1940s. The mixture was deemed suitable for construction but presented a health hazard during manufacturing.|
Advocates and suppliers say fly ash use improves concrete performance, making it stronger, more durable, and more resistant to chemical attack. One of the most important fields of application for fly ash is Portland Cement Concrete (PCC) pavement, according to the Federal Highway Administration, which encourages the use of fly ash in concrete.