NDT Technology for Quality Assurance of HMA Pavement Construction (2009) / Chapter Skim
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Pages 24-37
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From page 24... ...
The PSPA is used to test HMA mixtures, while the DSPA is used to test crushed aggregate base layers, embankments, and prepared subgrades. The DSPA was used on the shoulders of the US-280 reconstruction project instead of on the main roadway because the roadway base layer had been chip-sealed.
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From page 25... ...
Another advantage of this technology is that the system can be calibrated easily to the specific materials being tested during the mixture design stage for HMA materials or in developing M-D relationships for unbound materials. This calibration procedure allows the PSPA and DSPA to be used to detect volumetric, as well as physical, changes in the materials during construction.
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From page 26... ...
The GeoGauge provides elastic modulus values that are displayed on the gauge or stored in the device and downloaded to a computer at a later date. The resulting values were found to be similar to the resilient modulus values measured in the laboratory or calculated from the resilient modulus regression equations developed through the FHWA-LTPP program (Yau and Von Quintus 2002)
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From page 27... ...
As a replacement to the repeated load resilient modulus test, the regression equations developed from repeated load resilient modulus tests included in the LTPP program (Yau and Von Quintus 2002) or the use of the DCP is permissible.
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From page 28... ...
Similar to the PSPA, the operator needs more technical and sophisticated training in setting up the equipment and visually interpreting the deflection basin data. A separate data interpretation system or software is required for producing elastic modulus values from the measured deflection basins -- Young's modulus for each layer.
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From page 29... ...
Because the backcalculation procedures do not result in unique layer modulus values, it would be difficult to defend in contractor disputes where material has been rejected or payment penalties issued to the contractor. The device can be used to check or confirm the final flexible pavement for new construction or HMA overlays of existing pavements, but would probably create many disputes with the contractor when the entire pavement structure is rejected at the end of the project.
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From page 30... ...
However, there should be no difference between the procedures and the device's reaction to a hard base material and those of HMA mixtures. A key advantage of this technology is that it gives the operator a reading of the elastic modulus in about the same time required to obtain a nuclear density gauge reading.
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From page 31... ...
Most of the data reduction-presentation programs, however, still require some volumetric properties to be assumed in estimating density, air voids, and other volumetric properties. These assumptions result in error of the properties that are calculated from the dielectric values.
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From page 32... ...
32 Large aggregate particles in the embankment soil caused refusal of the DCP in localized areas. These particles found near the surface also had an impact on the DSPA and GeoGauge readings.
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From page 33... ...
In addition, the calibration requirements to improve on the accuracy of testing specific materials with the non-nuclear gauges are similar in detail and extent for nuclear density gauges. 1.6.1 Electrical Density Gauge An electrical density gauge was used in the Part A field evaluation projects, because of the equipment's perceived ease of use and application to a diverse set of unbound materials and soils.
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From page 34... ...
) is a light weight nonnuclear device for measuring the uniformity of HMA mixtures.
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From page 35... ...
However, this computed value is expected to be affected by the underlying support conditions. To date, the Evib value has not been evaluated or checked against dynamic modulus values measured in the laboratory or estimated through other NDT devices.
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From page 36... ...
1.8 Summary of Process Impact Table 13 provides a summary of process impact on flexible pavement construction for different NDT technologies and devices regarding their use in QA programs.
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From page 37... ...
NDT Technologies Deflection-Based DCP Non-Nuclear Devices Impact Topics or Issues Ultrasonic Gauges SteadyState Vibratory Trailer Portable Manual Automated GPR Non-RollerMounted RollerMounted Easily used to develop density or modulus growth curves? HMANo UnboundYes Yes No Yes No No No Yes Yes Resulting Value Seismic Modulus Elastic Modulus Deflection Deflection & Elastic Modulus Penetration Rate or Index Penetration Rate or Index Dielectric Values Density & Water Content Stiffness or Density Conversion required to adjust readings?
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