Sustainable Construction Case History: Fly Ash Stabilization of Recycled Asphalt Pavement Material

A case history is described where Class C fly ash was used to stabilize recycled pavement material (RPM) during construction of a flexible pavement in Waseca, MN, USA. The project consisted of pulverizing the existing hot-mix asphalt (HMA), base, and subgrade to a depth of 300 mm to form RPM, blending the RPM with fly ash (10% by dry weight) and water, compacting the RPM, and placement of a new HMA surface. California bearing ratio (CBR), resilient modulus (M_r), and unconfined compression (q_u) tests were conducted on the RPM alone and the fly ash stabilized RPM (SRPM) prepared in the field and laboratory to evaluate how addition of fly ash improved the strength and stiffness. After 7 days of curing, SRPM prepared in the laboratory had CBR ranging between 70 and 94, M_r between 78 and 119 MPa, and q_u between 284 and 454 kPa, whereas the RPM alone had CBR between 3 and 17 and M_r between 46 and 50 MPa. Lower CBR, M_r, and q_u were obtained for SRPM mixed in the field relative to the SRPM mixed in the laboratory (64% lower for CBR, 25% lower for M_r, and 50% lower for q_u). In situ falling weight deflectometer testing conducted 1 year after construction showed no degradation in the modulus of the SRPM, even though the SRPM underwent a freeze–thaw cycle. Analysis of leachate collected in the lysimeter showed that concentrations of all trace elements were below USEPA maximum contaminant levels.