Smartphone-based molecular sensing for advanced characterization of asphalt concrete materials
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Pavement systems deteriorate with time due to the aging of materials, excessive use, overloading, climatic conditions, inadequate maintenance, and deficiencies in inspection methods. Proper evaluation of pavement conditions provides important decision-support to implement preventative rehabilitation. This study presents an innovative smartphone-based monitoring method for advanced characterization of asphalt concrete materials. The proposed method is based on deploying a pocket-sized near-infrared (NIR) molecular sensor that is fully integrated with smartphones. The NIR spectrometer illuminates a sample with a broad-spectrum of near-infrared light, which can be absorbed, transmitted, reflected, or scattered by the sample. The light intensity is measured as a function of wavelength before and after interacting with the sample. Thereafter, the diffuse reflectance, a combination of absorbance and scattering, caused by the sample is calculated. This portable smartphone-based NIR method is used to detect asphalt binders with various performance grading (PG) and aging levels. To this end, a number of binder samples are tested in a wavelength range of 740 to 1070 nm. The results indicate that asphalt binders with different grades and aging levels yield significantly different spectrums. These distinctive spectrums can be attributed to the variations of binder components such as saturate, asphaltenic, resin, and aromatic. Furthermore, the molecular sensor is successfully deployed to detect and classify asphalt mixtures fabricated with a various binder and recycled material types such as styrene-butadiene-styrene (SBS), ground tire rubber (SBS), engineered crumbed rubber (ECR), reclaimed asphalt pavement (RAP), and recycled asphalt shingles (RAS). The proposed monitoring technology is not only a viable tool for asphalt material characterization but also a cost-effective platform capable of transforming the current physical and chemical methods for civil engineering material characterization.
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