4.2 List of Non-Destructive Tools in Order of Availability

The general order of availability for non-destructive tools is as follows:
  • Falling Weight Deflectometer (FWD).
     These systems are scheduled through the Pavement Evaluation office (Pavement Preservation, MNT) at (512) 832-7210.This device is essential in establishing the in situ stiffness properties of the pavement layers through analysis of the deflection data by backcalculation of layer moduli values using MODULUS. Moduli can then be used as design inputs to FPS 21.
  • Dynamic Cone Penetrometer (DCP).
     Many districts have purchased their own (roughly $2500 per unit). Units are also available at MNT – Pavement Asset Management. This portable device is a secondary tool used to verify unbound pavement layer thicknesses, confirm the presence of lime stabilized subgrade, and evaluate the relative stiffness and uniformity of support of unbound layers. It can prove useful in verifying MODULUS layer inputs and moduli outputs. A correlation equation developed by the Army Corps of Engineers is used to convert DCP data to moduli values. The DCP requires the boring of a small pilot hole through bound materials.
  • Air-coupled Ground Penetrating Radar (GPR).
     These systems are scheduled through the Pavement Evaluation office (Pavement Preservation, MNT) at (512) 832-7210. When department-operated systems are not available on short notice, the Texas A&M Transportation Institute (TTI) operates a system that may be available through an interagency contract managed by MNT – Pavement Asset Management.
    This is a van-mounted system that provides a nearly continuous profile of layer thicknesses and dielectric variations to a maximum depth of about 24 in. beneath the pavement surface. Dielectric properties are correlated to material density and moisture content so subsurface problems (stripping, trapped moisture) in the existing HMA and excessive moisture in base layers can be detected.
    GPR can also be used to identify segregation and low density in existing HMAs. GPR testing of PCC pavements has not been as successful as testing on HMA and surface treated pavements due to the GPR signal interference by the reinforcing steel and the attenuation of the signal through PCC materials.
  • Ground-coupled Penetrating Radar (GPR)
     testing is available from MNT – Pavement Asset Management and through an interagency contract with TTI that is managed by MNT – Pavement Asset Management. GPR testing involves pushing by buggy or towing one or more GPR antennae along the ground at walking speeds. Some antennae operate at a lower frequency than the air-coupled GPR units and, therefore, penetrate much deeper into the pavement and underlying layers. The trade-off with lower frequency antennae is poorer near-surface resolution. Ground-coupled GPR has been used to locate sink holes, search for buried underground objects, such as abandoned storage tanks, or test for water damage, underground utility problems, or other anomalies that are deeper than an air-coupled GPR unit can sense. These systems can explore anomalies under either flexible or rigid pavements.
  • Seismic-based tools (Portable Seismic Pavement Analyzer [PSPA], Dirt SPA [DSPA], V-meter, Free-free Resonant Column).
     Contact MNT – Pavement Asset Management for availability of these devices.
    The SPA series of devices are used in the field to measure in situ properties. These devices are used to generate seismic waveforms in the material being tested. The elastic modulus at small strain is proportional to the velocity of the wave propagation.
    The V-meter and Resonant Column are laboratory instruments used to measure properties of samples collected in the field or molded in the lab. These devices use a pin or hammer “source” to impact the pavement or sample surface. Wave propagation speed and analysis of the wave dispersion curves can be used to determine layer thickness, stiffness with depth, and presence of discontinuities (cracks, delaminations). Seismically-derived stiffness values are evaluated at very low strain and require adjustments to be used for determining values comparable to ones estimated at higher strains, for example, truck wheel loads.
  • Total Pavement Acceptance Device (TPAD).
     The TPAD was developed under a department research project that concluded in August 2012. Further implementation was authorized under a 2-year project through August 2014. The TPAD combines the capabilities of Rolling Dynamic Deflectometer (continuous deflection measurements) and air-coupled GPR surveys. Additionally, high definition video, linear offsets, high-precision differential GPS coordinates, and surface temperature logging of the pavement section are conducted concurrently. Coordinate use of this device through MNT – Pavement Asset Management.