The use of coal combustion bottom ash in lightweight masonry units

The production of coal combustion bottom ash exceeds 20 million tons in the United States and at one time was a major component in the manufacture of masonry units (a.k.a. "cinder block"). Quality issues such as staining along with substantial variations in size distribution have resulting in its being supplanted by other aggregates. This research has focused on the use of bottom ash as a major component in high value lightweight aggregate. Bottom ash from utilities consuming sub-bituminous as well as, high sulfur and low sulfur bituminous coals have been examined using a laboratory-scale pneumatic cylinder press and batch block machine to evaluate a variety of mix designs. It was found that by controlling the gradation and using fly ash as a filler at significant concentration that these materials were capable of producing excellent products. The results to date indicate bottom ash can again be an important source of aggregate in the US if processed to control size consist and remove impurities.