In May 2011 TRL acquired an E-Spott device, a Ground Penetrating Radar (GPR) system which can provide in the field spot depth measurements of total bound material thickness. A testing programme has been undertaken to assess the performance of this equipment and to determine possible applications.
Three E-Spott devices were used to assess the following on test sites at TRL and on local and trunk road networks: repeatability of an individual device; reproducibility of multiple E-Spott devices; coverage assessment; accuracy compared with coring and core calibrated GPR.
The experimental assessment has shown that E-Spott is quite repeatable and accuracy was reasonable. Best practice suggests that three repeat readings should be carried out. Direct comparisons with cores taken on site on the same day showed that, on average, E-Spott readings were within 10% of the core measurement for flexible pavements with thicknesses greater than 70mm.
E-Spott compares reasonably well with “traditional” GPR data that has been calibrated by coring. To make it sufficiently robust, E-Spott should not be used without the support of core data. Its accuracy is insufficient to negate the need for coring, but it can be used alongside targeted coring to improve efficiency and coverage. As a result, many more reinstatements could be checked for compliance and verification soon after construction. The data can also be used to target coring resources to confirm the status of reinstatements that the E-Spott data shows to be questionable.

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