Effects of fly ash and bottom ash on the frictional behavior of composites

Immense quantities of coal combustion by-products are produced every year, and only a small fraction of them are currently utilized. Our recent work has focused on developing value-added products especially from fly ash, bottom ash, and flue gas desulfurization (FGD) scrubber sludge. We explored the potential utilization of fly ash, bottom ash, and sulfate-rich scrubber sludge as frictional modifiers and additives for automotive frictional composites. The surfaces of the frictional composites, fabricated from scrubber sludge and fly ash or bottom ash, were characterized with the help of scanning electron microscopy (SEM). The mechanical properties of by-products containing composites were evaluated using a dynamic mechanical analyzer (DMA). The frictional behavior of the composites was probed with the help of friction assessment and screening test (FAST). The frictional results suggested that fly ash or bottom ash had a profoundly different effect on the frictional coefficient (mu) and wear of the composite than those observed for scrubber sludge particles. It appeared that fly ash or bottom ash particles had abrasive characteristics and gave frictional composites a higher mu -value. The FAST test also revealed that the fluctuations in the mu -value were a minimum for composites that contained 20 vol% fly ash or bottom ash among the ash-derived composites. The composites that contained 30 vol% fly ash or bottom ash showed fade after approximately 60 min of continuous FAST test. We compared the frictional and wear performance of our composites with a commercial automotive brake, and it appeared that frictional composites could be formed which contained up to 20 vol% fly ash or bottom ash and 25 vol% scrubber sludge. (C) 2001 Elsevier Science Ltd. All rights reserved.