Evaluation on the Use of Coal Combustion By-Products in Highway and Airfield Pavement Construction (2969-1F)

The objective of this study was to exploit the beneficiation and utilization of coal combustion by-products (CCBPs) as low-cost alternate aggregates and stabilizers in roadway and airfield construction. A literature review and laboratory investigation were performed to investigate the use of CCBPs in three highway construction applications: (1) fly ash for subgrade stabilization, (2) flue gas desulfurized (FGD) gypsum and Gypsite for base and subbase construction materials, and (3) bottom ash (with sulfur modification) in asphaltic concrete mixtures.|Results from field trials utilizing CCBPs in roadbases indicate good to excellent performance characteristics and negligible environmental impact. Class C and lime-enhanced Class F fly ashes were shown to be effective stabilizers for both clayey and sandy soils. The field trials showed that sulfate-resistant cements and Class C fly ashes provide a wide range of strengths in stabilized sulfate and sulfite roadbases.|The use of sulfur improved the crushing strength and reduced the asphalt demand associated with bottom ash in asphaltic concrete mixtures. Sulfur modification required asphalt contents equal to and often less than for mixtures using conventional aggregates.|Based on its availability, lower cost, safe use, and demonstrated performance, CCBP materials should find increasing use especially in those regions of Texas experiencing dwindling or non-existent aggregate sources.