Boral tests high LOI, impounded ashes for lightweight aggregate

Sources: Boral Resources, Atlanta; CP staff

The leading marketer of ASTM C618-grade fly ash has secured U.S. rights for processing ceramic lightweight aggregate from high carbon residuals generated at coal-fired power stations or impounded at their sites or designated landfills.

“This technology offers an opportunity to utilize both high- and lower-quality fly ash resources in the production of a high-value construction material,” says Boral CM Services Vice President, Technology Rafic Minkara, Ph.D., P.E. “It is ideal for utilizing ash harvested from disposal impoundments that are being closed in response to environmental regulations.”

The technology utilizes a proprietary dryer and a high-temperature/high-efficiency rotary kiln to convert raw feed to sintered spherical pellets. The sintering operation is autogenous, as it does not require external fuel aside from the coal remaining in feed material. The excess heat production capacity can be used for hot water or converted into electricity, representing an additional revenue stream. 

Automated production based on the technology can be overseen by as few as four people. It allows for set up as a a) separate, stand-alone operation to process pond- or landfill-derived material, or b) integrated installation to be incorporated into a power plant for aggregate production and heat recovery. The process yields a concrete-grade aggregate of ceramic composition, chemically neutral and bearing physical characteristics equating to potentially wider application than natural aggregates. The product has bulk density ranging from 35-45 lbs./cu. ft.; high strength-to-weight ratio; resistance to fungi, mildew, fire and the effects of freeze-thaw cycles; plus, heat and sound insulation properties.

Since 2015, a full-scale production plant in Poland has processed coal ash from a utility landfill as feed material, yielding approximately 50,000 metric tons of lightweight aggregates annually. The material has been sold domestically and exported for high performance concrete.