Preliminary engineering, monitoring of construction, and initial performance evaluation: use of ponded fly ash in highway roadbase

Abstract

This report summarizes findings of laboratory and field trial evaluations of ponded fly ash used as a component in a stabilized aggregate base course. Ponded fly ash is the fine portion of pond ash which is a by-product of a coal burning process and is disposed by sluicing to a disposal pond. Three stabilized aggregate base mixtures containing various proportions of dense graded aggregate, ponded fly ash, and hydrated lime were evaluated in the laboratory relative to maximum dry density, optimum moisture content, and unconfined compressive strength. The mixture that was selected for field trial evaluation had the highest unconfined compressive strength and consisted of 85 per cent dense graded aggregate, 11 per cent ponded fly ash, and 5 per cent hydrated lime. A 750-foot section of a 22-foot wide roadway was constructed in May 1988. Approximately 80 tons of ponded fly ash were utilized in constructing the experimental base. Prior to construction, in-place California Bearing Ratio tests, moisture content determinations and Road Rater deflection tests were performed on the prepared subgrade. The stabilized aggregate base was placed in one 8-inch lift. During construction, relative compaction and moisture content of the base material were monitored by nuclear devices. Post construction evaluations included Road Rater deflections tests and coring to obtain samples for laboratory evaluation. To date, the section containing the stabilized aggregate base is performing very well in comparison to the conventionally paved section (A).