The National Academies

NCHRP IDEA 20-30/IDEA 138 [Completed (IDEA)]

Scanning Capacitive Arrays for Real-Time, In-Situ Imaging of Density and Thickness in HMA Roadways
[ NCHRP 20-30 (NCHRP-IDEA) ]

  Project Data
Staff Responsibility: Dr. Inam Jawed

The goal of this project was to develop a method for measuring HMA density via an array of sensors capable of rapidly inspecting large areas. Through work performed in the project, the researchers were able to demonstrate desired measurements with a working prototype.  The prototype sensor was designed to be one element of the multiple-element sensor array.  It was about 2.5 inches high, had an active element length of 12 inches, and was equipped with wheels. The active area of the sensor included electrodes for generating the electric field (drive electrodes) and four sets of sensing electrodes, sensitive to material properties at varying depths (patents issued and pending). In the demonstration, this prototype sensor was used to scan four 1.5 inch thick lab-produced Superpave HMA-lift specimens (two at about 86% density and two at about 91% density). Data from two sensing electrodes acquired at 10 MHz were used to estimate the effective dielectric permittivity of the HMA in the specimens, using Jentek Multivariate Inverse Methods. The estimated permittivity exhibited strong correlation with the HMA density and the measurements were repeatable.  This prototype sensor is designed to be a part of a 19-sensor array, enabling rapid, wide, detailed, full coverage of a 10 foot wide scan path.  Jentek’s parallel-architecture 39-channel instrument can simultaneously acquire single-frequency data from all sensors in the array at a rate higher than 100 measurements per second.  The researchers need funding opportunities to transition this prototype to a commercial product.  The contractor's final report is available.

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