The concept of taking a throw-away material and converting it into an aggregate that meets construction industry standards would benefit both the environment and the construction industry. Municipal Services Corporation (MSC) has developed a synthetic aggregate manufactured from ash recovered from the incineration of municipal solid waste (MSW).
In the patented MSC process, the ash is broken down into its basic components, mixed with binders and chemical fixation agents to permanently immobilize heavy metals of concern, and pelletized on a pan pelletizer into a graded aggregate. In development of the product, special attention was given to the absorption of asphalt cement which was initially high, but which was brought to within acceptable limits through a process modification.
The aggregate, known under the trade name “TAP”, or Treated Ash Product, was shown in the laboratory to meet Minnesota DOT physical testing requirements for aggregates in bituminous mixtures. In preliminary asphaltic concrete mix design testing, Marshall Stability properties were in the range of 2000 – 2500 lb (8900 – 11,120 N), but asphalt demand was high (7.5%). The problem was addressed by coating the TAP with lime. Subsequent Marshall Stability values averaged 2540 lb (11,300 N) at an asphalt cement content of 5.7%. In environmental testing, the TAP leachate met current federal drinking water standards after being ground to a fine powder and subjected to the U.S. EPA's TCLP (SW 846-1311), an acid leaching test.