Infrasense Uses GPR to Measure Pavement Density for the Minnesota DOT

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Infrasense has recently developed a system for measuring and mapping asphalt pavement density using ground-penetrating radar. The system was designed to work with the Minnesota Department of Transportation's existing GPR setup, and to be used immediately after construction to identify areas of potential low density. Pavement density is an important component of Quality Control and Quality Assurance of new pavement construction, and Minnesota is evaluating GPR as a QC/QA tool.

MnDOT Survey Van with Single Horn Antenna

Infrasense, Inc. has recently collaborated with the Minnesota Department of Transportation (MnDOT) to develop and implement a system for measuring and mapping asphalt pavement density using ground-penetrating radar (GPR). Achieving the target density for a pavement is particularly important for long term pavement performance. Pavement density is a measure of Quality Control and Quality Assurance (QC/QA) of new pavement construction projects. Traditionally, density has been measured by MnDOT using cores. However, cores provide data at only a limited number of random locations. Other organizations supplement cores with data from a nuclear density gauge, but this requires special licensing and is also limited in the amount of data provided. The GPR-based system developed by Infrasense provides 100% coverage of the entire pavement, revealing potential patterns of low density, such as along joints and at stopping points. The system has previously been implemented by the Florida DOT.

Infrasense’s GPR system for pavement density measurement consists of a single or dual air-coupled radar antenna (s) mounted to the front or back of a survey vehicle. The GPR data is collected in a series of lines spaced 2 feet transversely across the width of the pavement, with each line representing a cross sectional slice of the pavement at a particular offset. Infrasense integrated a photo-reflective laser switch into the system to automatically insert marks in the GPR data for the start and end of the section being surveyed. Infrasense modified the antenna settings to enhance the near-surface resolution of the data and to collect data more frequently than traditional GPR surveys. In order to assess the pavement on-site, Infrasense developed processing software (GPRQA) that automatically analyzes the GPR field data to produce color contour maps of the asphalt surface. The analysis can be carried out on site or in the office. By analyzing these maps on-site for stronger and weaker dielectrics, cores can be taken at optimum locations for calibration.

The purpose of this project was to develop and implement a density evaluation procedure for new HMA pavements using the existing GPR system owned by the Minnesota DOT. The procedure can be used immediately after construction to identify areas with potential low density. Initial field trials were carried out at two state highways with ongoing pavement construction projects. Cores were taken at locations chosen using the processed contour maps, and the cores were tested in the MnDOT laboratory to obtain direct density measurements. The cores showed a strong correlation between plotted dielectric values and percent-maximum density values at the core locations. The results from these two projects are being used by MnDOT to evaluate use of GPR as a QC/QA tool in pavement construction projects.

About Infrasense, Inc.

Since 1987, Infrasense, Inc. has applied the most current technologies to the most difficult challenges in subsurface scanning. Infrasense’s engineers are able to nondestructively extract critical information from a diverse range of structures. The firm has conducted research to advance the field of subsurface detection, while also providing valuable information to clients across the country. Learn more about Infrasense, Inc. and its services at http://www.infrasense.com.

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Ken Maser
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