Project title: Nano-engineered Smart Tarmacs for Detecting Distributed Surface and Subsurface Pavement Damage
Source of support: Federal Aviation Administration
Airport pavements and runways suffer from damage due to severe operational and environmental loads. Knowing damage severity and location a priori, usually nondestructively, is crucial for facilitating maintenance and directing repair efforts. The goal is to maximize transportation safety and efficiency while minimizing operations and repair costs. In fact, a plethora of technologies are available and used for monitoring pavement damage. For instance, coring of the runway can provide information regarding each pavement layer and the interlayer boundaries, but it is a destructive procedure in order to extract such a sample for testing, and the hole must be filled. Other techniques such as impact-echo and acoustic methods, as well as ground penetrating radar, offer unique advantages, but these tests only measure pavement condition at a single point and can be sensitive to environmental conditions. More recently, the research community has dedicated tremendous effort in designing next-generation smart cementitious composites and pavements, usually by mixing conductive additives (e.g., carbon black, carbon nanofibers, and carbon nanotubes) in the cement matrix. However, dispersion of conductive additives is challenging, and large concentrations of additives are typically required, which increase costs and decrease workability of the mix.
The goal of this project is to develop multifunctional, nano-engineered, cementitious composite pavements that can not only bear loads but can also self-sense damage occurring in the material. Instead of mixing and dispersing nanomaterials directly into the cement matrix, this new class of "smart concrete" was designed using a new approach based on modifying the cement-aggregate interface. Here, carbon nanotube-based thin films were first deposited onto coarse and/or fine aggregates using a spray-coating technique. Once the films have dried, the film-enhanced aggregates were then used as is for casting cementitious composites. Using this method, two orders of magnitude fewer nanotubes were needed in order for the cementitious composite to be electrically conductive. Electromechanical test results revealed that their mechanical properties were comparable to their pristine counterparts, yet the material's electromechanical properties were also sensitive to applied strains/stresses. Furthermore, in order to achieve damage detection and localization, an electrical resistance tomography (ERT) was derived and implemented. Tests conducted in the laboratory showed that ERT was able to map the distribution of electrical properties of smart concrete specimens. In addition, damage detection and localization was successfully validated.
Fig. 1. (a) A smart concrete plate was subjected to damage by drilling three holes in the plate. (b) The corresponding ERT results clearly identified localized increases in electrical resistance corresponding to the locations of drilled holes.
Fig. 2. (a) A smart concrete plate was subjected to crack-like damage by sawing two cuts on the surface of the plate. (b) The corresponding ERT result successfully identified localized increases in material resistance corresponding to the cuts.