A major concern for using recycled pavement material as an unbound base or subbase layer is the effect of changing seasons on the properties of the recycled material. Three sources of recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP), and one conventional base aggregate, were used to investigate the effect of freeze–thaw cycles on the stiffness of unbound road base/subbase layers. Effects of freeze–thaw cycling on the mechanical behavior of three gradations (coarse, medium, fine) of recycled materials were systematically evaluated to determine how climatic factors and aging affect the resilient modulus. Sealed specimens were exposed to 5, 10, and 20 sets of freeze–thaw cycles. Resilient modulus tests were conducted according to NCHRP 1-28A after the final freeze–thaw cycle. Freeze–thaw cycling caused a decrease in the stiffness (i.e., the summary resilient modulus) of RAP samples and class 5 aggregate because of the effect of the water retained in the pores. An increase in the stiffness of RCA was observed over 20 freeze–thaw cycles and is attributed to self-cementitious behavior of crushed concrete. Seismic modulus testing was used to investigate the continuous rate of change (daily) of the stiffness for RCA and class 5 aggregate. The seismic modulus test confirmed the trends observed in resilient modulus testing and served as a non-destructive method for tracking changes in stiffness over time and freeze–thaw cycling.