Stiffness Properties of Recycled Concrete Aggregates as Unbound Base and Subbase Materials Under Freeze and Thaw Cycles

Freeze and thaw processes are mostly observed in cold regions and impact the short- and long-term performances of road pavements. Thus, freeze and thaw processes should be considered when designing and constructing roads due to the potential change it will cause to the structure, arrangement and properties of the materials used in road construction. This study attempted to understand the effect of freeze and thaw (F–T) cycles on the stiffness properties of recycled concrete aggregates (RCAs). For this purpose, base and subbase samples prepared with RCAs are subjected to varying numbers of F–T cycles, and a series of resilient modulus and permanent deformation tests are conducted. Moreover, the different models were applied to estimate the resilient modulus and permanent deformation, and the suitability of each model was discussed. The experimental study results indicate that the geotechnical engineering properties of RCAs originating from Istanbul-Turkey are suitable for utilization as unbound base or subbase course materials. In the stiffness assessment, the highest resilient modulus was obtained after 5 F–T cycles and then decreased but was still higher than that of the nonfrozen samples except the subbase sample exposed to 20 F–T cycles. Lower plastic strain values were obtained for the base samples, and after F–T exposure, no drastic changes were observed in the permanent strain increments for the base materials, as seen in the subbase samples. Most of the RCA samples exposed to F–T cycles accumulated permanent strains with plastic creep behavior based on the shakedown theory.