Monitoring internal strains in asphalt pavements under static loads using embedded distributed optical fibers

This study explored the feasibility of using an embedded distributed optical-fiber sensors (DOFS) for providing a fully-distributed measurement in pavement structures, in particular that uses Rayleigh-scattering-based optical frequency-domain reflectometry (OFDR). Due to the novelty of this technology, and inherent heterogeneity, roughness and flexibility of pavements, the application of DOFS to asphalt pavements presents several uncertainties in terms of their durability, robustness and long-term stability. Therefore, a series of laboratory tests were performed to examine the performance of a packaged DOFS for measuring the responses under static loads for two types of pavement with different stiffnesses. The packaged DOFS uses a single-mode polyimide-coated optical fiber that is protected by a sheet-type sealing material and covered by a flexible smart mortar. The sensitivity of embedded DOFS was also assessed for three embedment depths (5, 10 and 20 mm). Although the raw data obtained from the DOFS contained a few outliers in some cases, it could obtain the full strain distribution with a high spatial resolution of 0.65 mm, and with a sensitivity similar to that of the traditional strain gauges. Moreover, the location of a load and the time-dependent strain response of the pavement could also be identified.