Principles of Ground Penetrating Radar (GPR) for Pavement Evaluation

Ground penetrating radar operates by transmitting short pulses of electromagnetic energy into the pavement using an antenna attached to a survey vehicle. These pulses are reflected back to the antenna with an arrival time and amplitude that is related to the location and nature of dielectric discontinuities in the material (air/asphalt or asphalt/concrete, reinforcing steel, etc). The reflected energy is captured and may be displayed on an oscilloscope to form a series of pulses that are referred to as the radar waveform. The waveform contains a record of the properties and thicknesses of the layers within the pavement.

The sequence of scans is frequently coded in color or gray scale to produce the "b" scan representation, which provides the equivalent of a cross sectional view of the pavement, with the individual pavement layers showing up as horizontal bands. The white and black bands indicate stronger reflections and occur when the dielectric contrast is greater. The grey regions indicate weaker reflections and occur when there is little dielectric contrast. Layer thickness is calculated from the arrival time of the reflection from the top and bottom of each layer, and the dielectric constant of the layer.

Computation of the dielectric constant of the surface layer can be made by measuring the ratio of the radar reflection from the pavement surface to the radar amplitude incident on the pave­ment. The incident amplitude on the pavement is determined by measuring the reflec­tion from a metal plate on the pave­ment surface, since the metal plate reflects 100% of the incident energy. A similar calculation can be made for the dielectric constant of the base material. Changes in base moisture content have a strong effect on the base dielectric constant, and thus the base dielectric constant can be used as an indicator of high moisture content.

The calculations described above are automated in Infrasense’s winDecar© data analysis software program for computing pavement layer thickness and changes in pavement layer properties. The analytical techniques described above serve as the basis for data analysis carried out during Infrasense’s pavement projects.

 

Select Pavement Evaluation Projects

Structure Database for Idaho Districts 4 and 6

Infrasense developed a roadway structure database for Districts 4 and 6 to assist future planning efforts. The final deliverable was a pavement structure geodatabase built in ArcGIS, and included GPR, FWD, and core data with calculated structural number and remaining life of different pavement sections. Learn more...

24 Regional Airports in South Carolina

We provided pavement layer thickness information to facilitate FWD back-calculation efforts, and ultimately the determination of Pavement Classification Numbers (PCNs) for all airport pavement facilities (runways, taxiways, aprons). Additionally, we provided the location of any detected voids and utilities. Learn more…

4000+ Miles of County Roads in North Dakota

Infrasense provided pavement layer thickness values at FWD test locations for over 4000 lane-miles of county and local roads across North Dakota. This subsurface pavement information was part of a larger statewide study carried out by NDSU’s Upper Great Plains Transportation Institute to assess infrastructure needs related to agriculture and oil shale development. Learn more…

Composite Pavement Structure and Condition Mapped in Connecticut

We used a vehicle-based GPR system to scan a 2.8-mile section of pavement in East Hartford in order to locate changes in the pavement structure. Additionally, GPR was used to identify areas of deterioration in the underlying PCC pavement layer. Falling Weight Deflectometer (FWD) testing was performed to assess load transfer efficiency at targeted slab joints. Learn more...

Density of New HMA Pavement Mapped in FL, MN, CA, ME, NH, and WS

Infrasense used GPR to map of the relative density of new HMA pavements. This relatively new application is being utilized as a quality assurance measure to compliment recently developed quality control systems, such as Intelligent Compaction. Learn more…

Pavement Structure Type Defined along the Cleveland Memorial Shoreway

We used high-speed GPR to map changes in the pavement structure along the Cleveland Memorial Shoreway. The results were presented geospatially with different color line segments corresponding to different pavement structure classifications. Learn more…