Field Evaluation of Fly Ash Stabilized Subgrade in US 12 Highway

This paper describes a case study where subgrade soils were stabilized with Class C fly ash to create a working platform during reconstruction of a 1.2-km section of rigid pavement in US 12 between Cambridge and Fort Atkinson, Wisconsin. The subgrade soils were blended with cementitious fly ash to increase its bearing resistance and stiffness. Resilient modulus (M_r), unconfined compression strength (q_u), soil stiffness gauge and dynamic cone penetrometer tests were conducted on the subgrade alone and fly-ash stabilized subgrade (FASS). Falling weight deflectometer (FWD) tests were conducted on the as-built pavement. After 14 d of curing, M_r of the field-mixed FASS ranged between 60 and 129 MPa and M_r of the laboratory-mixed FASS ranged between 115 and 167 MPa, whereas the M_r of subgrade was between 34 and 42 MPa. q_u of the laboratory-mixed FASS was four to nine times the q_u of the subgrade, while q_u of the field-mixed FASS was up to three times q_u of the subgrade. In situ stiffness and dynamic penetration index also illustrated that the addition of the fly ash and compaction increased the strength and stiffness appreciably. Moduli back-calculated from FWD tests showed that the modulus of the FASS varies seasonally.