Fly-Ash Bases in the Atlanta District: Evaluation of Surface Treatment Bond and Year-Two Field Performance Evaluations (7-2966-2)

Hydrated fly ash is produced by allowing powder fly ash (Class C) from coal power plants to cure with moisture. The hydrated (cured) fly ash becomes a stiff material that can be crushed to form a synthetic aggregate. When properly processed and compacted to optimum moisture content, the hydrated fly ash continues to gain strength after placement as a base material.|The Atlanta District has constructed six pavement sections since 1993 using hydrated fly ash as the flexible base material. This research project was initiated to evaluate and monitor performance and changes in material properties for these six pavements through the year 2001 and to evaluate a problem experienced during construction where the asphalt surface treatment did not bond well to the base.|A laboratory study was performed to investigate the bond strength of different types of prime materials to the fly-ash base. Curing extent of the base was also a variable in the experiment. Results of the laboratory study revealed that the type of prime material used during construction did not contribute to the inadequate bond achieved. It is more likely attributable to the extent of base cure prior to application of an asphalt membrane. Construction recommendations are provided in this report aimed at achieving adequate bond of the surface treatment to the fly-ash base.|Evaluation of pavement base performance was based on visual documentation, falling-weight deflectometer tests, ground penetrating radar, and compressive strengths of field cores. This report is an interim report documenting the performance evaluations conducted in the spring of 1998. This report covers the second annual evaluation in a series of five.