Analysis of Fly Ash as a Partial Substitute for Portland Cement to Minimize Freeze-Thaw Damage in Cement-Treated Base

The use of cement-fly ash (CFA)-stabilization has been successfully implemented in roadway construction to produce strong base layers; however, the freeze-thaw durability of this material has not been adequately studied. The objectives of this research were to assess the freeze-thaw durability of CFA-treated base and then compare the performance of CFA-treated base to standard cement-treated base (CTB). Material from a reclaimed flexible pavement was used to create unconfined compressive strength (UCS) specimens in a controlled laboratory environment. The specimens were treated with either CFA (cement-to-Class F fly ash ratio of 4:1 by weight) or cement at one of two stabilizer contents and cured for 7 days, 28 days, or 6 months. The specimens were then conditioned with either a 4-hour soak or vacuum saturation, where the latter was performed as a much faster alternative to standard freeze-thaw durability testing. An analysis of variance was used to identify the factors that were statistically significant in explaining variation in the observed UCS of the treated material. All CFA-treated specimens had a 7-day UCS above 300 psi and exhibited adequate durability. The average UCS of the CFA-treated specimens was 88 percent of the average UCS of the cement-treated specimens, which translates to a decrease of only 80 psi. The data are inconclusive to suggest that a partial fly ash substitution would reduce freeze-thaw damage of standard CTB. Nonetheless, CFA base stabilization appears to be a viable option for producing a strong and durable layer for cold regions pavements.