Structural Performance of Foamed Asphalt Base in a Full Depth Reclaimed and Sustainable Pavement

Environmental awareness and budgetary constraints in road construction and rehabilitation require innovative and at the same time environmentally friendly solutions in favor of resource conservation, in any type of pavement intervention. In the meantime, surface interventions in severely deteriorated pavements are insufficient, increasing as such the recycling potential of existing materials in Full Depth Reclamation (FDR). This study addresses the efficiency of an FDR process in which the recycled base course of an existing semi-rigid pavement is stabilized with Foamed Asphalt (FA). The adverse effects of FA curing, which have a significant impact on pavement evaluation, particularly in the early stages of a pavement’s life cycle, prompted the conduct of a comprehensive testing campaign at two different periods, shortly after pavement rehabilitation and five years thereafter. The campaign included nondestructive testing at the aforementioned periods using Ground Penetrating Radar (GPR) and the Falling Weight Deflectometer (FWD), which facilitate the structural evaluation of the FA base. Using the collected nondestructive testing data, the principles of Multi-Layer Elastic Theory (MLET) and Genetic Algorithms (GA) are used to investigate the performance of the FA base. Both analysis tools captured the FA strength increase in the second period, but an increased variance of the FA modulus was observed mainly in the first test period, probably due to the curing effect. In addition, GA showed an advantage over other, more conventional tools for back-analysis of pavement stiffness, resulting in an interesting correlation potential of FA modulus to a deflection-based parameter reflecting the condition of the FA layer. Overall, the study contributes to the development of a practical methodology suitable for the evaluation of non-conventional and sustainable pavement structures.