Smartphone-based molecular sensing for advanced characterization of asphalt concrete materials

Abstract

Pavement systems deteriorate during time due to the aging of materials, excessive use, overloading, climatic conditions, inadequate maintenance, and deficiencies in inspection methods. Proper evaluation of the pavement condition provides important decision support to implement preventative maintenance or to plan for rehabilitation. This study presents an innovative 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 after contacting the surface of the sample. The light intensity is measured as a function of wavelength before and after interacting with the sample. Thereafter, the diffuse reflectance reflected by the sample, as influenced by absorbance and scattering, is measured. The proposed portable smartphone-based NIR method is used to characterize asphalt binders with different grades, aging levels, and rubber contents. To this end, a number of binder samples are tested in a wavelength range of 740–1040 nm. The results indicate that asphalt binders with different grades and aging levels yield significantly different spectra. These distinctive spectra can be attributed to the varied amounts of binder components such as asphaltenes, resins, and aromatic fractions, and molecular arrangements associated with varied levels of oxidative hardening (ketones, carboxylic acids, phenols, quinolones, etc.). Furthermore, the molecular sensor is successfully deployed to detect and classify asphalt mixtures fabricated with various binder and recycled material types such as styrene–butadienestyrene (SBS), ground tire rubber (GTR), engineered crumbed rubber (ECR), reclaimed asphalt pavement (RAP), and recycled asphalt shingles (RAS). The proposed monitoring technology can be considered as a cost-effective platform capable of transforming the current physical and chemical methods for civil engineering material characterization.