Sensors & Software PDP1000, User Manual

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PDP User's Guide Methodology
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5. Methodology
This chapter explains the basic theory, use scenarios and methodology for using
PDP.
NOTE: Since PDP measures surface reflection, do not use this during rain or on
wet pavement as this will produce incorrect values. PDP is intended for use on
fresh asphalt.
5.1 Importance of density measurements
The life of asphalt pavement has been demonstrated to be dependent on the
consistency and uniformity of paving. Measuring the density of the final
compacted asphalt is an accepted way of assessing the quality and consistency.
After paving, density is often obtained by taking cores. Cores are destructive and
the holes must subsequently be repaired. In addition, cores provide only point
measurements, and most of the time do not provide adequate sampling coverage
over an area. Non-destructive methods (such as nuclear density and dielectric
gauges) do not damage the asphalt, but only offer point measurements, which is
not representative of an entire asphalt pour.
5.2 How PDP works
PDP is based on Ground Penetrating Radar (GPR) technology. It works by
measuring the bulk electrical properties of the asphalt based on the reflected radio
wave from the surface of the material.
A radio wave is transmitted from the PDP sensor downward towards the asphalt.
When the wave hits the asphalt surface, some of the energy is reflected back to the
PDP sensor, while the remainder travels down through the asphalt. The magnitude
of the reflected wave is measured and is a direct indicator of the dielectric
permittivity (K) of the asphalt. This value must be translated into the desired
measurement, that being density.
5.3 Usage scenarios
Most users will want to use PDP right after asphalt compaction to check for
uniformity or any anomalous areas.
PDP can be used to collect a profile of data over an area, providing a plot of K vs
position. Or it can take measurements while stationary showing the distribution of
K values at a specific location.
In terms of user scenarios, there are three main approaches: