One of the key elements in pavement rehabilitation is the collection of valuable engineering data. A great companion to the FWD, the Ground Penetrating Radar (GPR) is a non-destructive testing device that is able to paint a detailed picture of what lies beneath the pavement surface. The GPR uses high frequency radio signals transmitting at regular intervals into the ground. When the wave hits a boundary with different dielectric constants, the receiving antenna records variations in the reflected return signal, identifying pavement layers and burried objects.
Features of the RoadScan™30 System
– SIR-30, the new generation radar control unit capable of acquiring 5,792 scans per second. Data from both antennas are collected into one file.
– Smart ID module air-coupled antenna with 2.0 GHz centre frequency, alowing data collection at highway speed. Effective depth penetration on pavements is 0.5 – 0.75 m
– High-speed smart ID ground-coupled antenna with 400 MHz centre frequency, alowing data collection at speed up to 60 km per hour. Effective depth penetration on pavements is typically 2-3 m, max 5 m
– DMI and GPS data are linked to each radar signal
The RoadScan™30 mainly provides an effective tool for quickly determining pavement layer thickness. GPR does not replace the need for boreholes and cores, however, it allows reduction in their number, and thus reduces impact on traffic operations. It also provides in-filling in areas that are inaccessible to a drill rig, such as road sections with numerous underground utilities or freeway lanes that are difficult to close to traffic. Documented studies show that GPR pavement thickness measurements typically fall within 2-10% of core values for the bound layers, while lower deviations (2-5%) are generally associated with newly constructed pavements. Significant progress has taken place in developing techniques for density testing of newly constructed asphalt pavements by using dielectric values.
Other applications include bridge deck assessments and wet sub-surface area mapping.
Typical use of GPR data:
- Pavement management – an efficient tool for quickly collecting inventory data, setting priorities and allocating resources.
- Rehabilitation design – accurately identifying pavement thickness variation, transitions and modifications of existing structures.
- Asphalt milling – insuring proper depth control for mill and fill rehabilitation and cold in-place recycling.
- Construction of new pavements and overlays – GPR can provide a faster, non-destructive and more complete means of obtaining QA/QC data than coring.
- FWD testing – since back-calculated layer resilient moduli is heavily influenced by layer thickness (never uniform along pavement), the use of estimated or averaged numbers produce significant errors. FWD and GPR devices are considered to be the best combination for effectively measuring asphalt concrete modulus and layer thickness.
Collected GPR scans are processed using Radan 7 software. Processed data can be displayed as radar images, or can be exported in the form of a text file. KML files can be downloaded to Google Earth with predetermined parameters (such as ranges of layer thickness).