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TRANSPORTATION RESEARCH DIGEST

ARIZONA TRANSPORTATION INSTITUTE

e-mail jsemmens@cox.net

NOVEMBER 2005

Section evaluates the physica1 GPR detection limitations. The second part of the Results and Discussion Section presents the thicknesses of the pavement layers in the Virginia Smart Road, as predicted with the GPR surveys. An evaluation of the GPR thickness prediction accuracy is also presented in this section. The third part of the Results and Discussion Section shows how GPR was used to control the installation of the reinforcing mesh installed within the pavement. The last part of the Results and Discussion Section presents a methodology to measure the complex dielectric constant of the different Superpave mixes used in the Virginia Smart Road.

Conclusions

GPR testing at the Virginia Smart Road allowed the evaluation of the performance of GPR when used for nondestructive testing of flexible and rigid pavements. This evaluation was facilitated by the full knowledge of the different structures and compositions of the various sections of the road, in addition to the embedment of copper plates (perfect EM reflectors) at the different layer interfaces during construction of the pavement. The following findings are presented:

1.

Use of GPR to nondestructively estimate the layer thicknesses of aggregate, HMA, and concrete layers is validated. The error of the HMA layer thickness was found to be around 3% when the individual layers were resolved in the GPR reflected signal. The error increased to 12% when the overall HMA layer was considered without resolving the thin layers

2.

A technique to estimate the variations, versus frequency, of the in-situ dielectric properties of HMA layers was developed and validated.

3.

The effect of the variations of the dielectric properties within the GPR bandwidth is found to be insignificant vis-a-vis the accuracy of thickness estimation.

4.

GPR can successfully be used as a quality control tool during pavement construction to ensure that the constructed layer thicknesses conform to the design. This nondestructive technique can be considered as a better alternative to coring since it does not disturb the pavement structure and provides continuous thickness information along the constructed section. GPR surveys can be conducted as soon as the HMA layer is hard enough for driving on it (i.e., 4 to 5 hours after placing the layer).

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