Demonstration of Ash Utilization in Low Volume Roads

Two field projects are described where cementitious fly ashes (10% by dry weight) and water were mixed to stabilize recycled pavement materials and road-surface gravel to form a base during reconstruction of a city street in Waseca, MN, and construction of a flexible pavement in a segment of gravel country road, CR 53 in Chisago County, MN, respectively. Addition of fly ash improves the stiffness and strength of the base materials significantly. A resilient modulus of minimum 50 MPa appears safe to assume irrespective of the base material at the end of construction due to fly ash stabilization. However, moduli of 100 MPa or more can also be achieved. There is no evidence of frost-induced degradation in the field over a single season of winter. Chemical analysis of the draining leachate from the fly ash-stabilized layers showed that the concentrations of trace elements (with the exception of Mn) were below USEPA maximum contaminant levels and Minnesota health risk levels. Longer-term monitoring is needed to fully understand the potential for leaching of trace elements and frost action during the service life. These field cases show that fly ash stabilization provides an effective and economical means of providing a base for asphalt paving using existing roadway materials.