Network Level Pavement Structural Testing With the Traffic Speed Deflectometer

About the report:

This report describes research conducted to incorporate pavement structural condition information obtained from the Traffic Speed Deflectometer (TSD) into the Virginia Department of Transportation (VDOT) pavement management system decision making process for bituminous pavement sections. Testing was conducted on a 4,000-mile (1,500 interstate miles and 2,500 primary roads miles) subset of the VDOT network. The report showed that the pavement structural condition, as measured by the TSD, has an impact on the rate of deterioration of the pavement surface. In addition, for the set of collected data, the consistency between the TSD and Falling Weight Deflectometer (FWD) in identifying the same weak sections was found to be higher than the consistency between repeated sets of FWD measurements performed in the Bristol district. The consistency was defined as the percentage of structurally weak sections identified by both devices as a proportion of the number of weak sections. Also, the distribution of the effective structural number (SN_eff) calculated from the TSD measurements on interstate roads was found to be similar to that obtained from the FWD measurements. The relatively good consistency between the TSD and FWD SN_eff and the similarities between the SN_eff distributions suggest that the structural information derived from the TSD can be successfully used as an alternative to similar data derived from the FWD for VDOT network level pavement management applications.

The resilient modulus (M_R) based on FWD testing is a metric currently used by VDOT to characterize the subgrade strength. A number of TSD-based indices have been proposed in the literature to replace the FWD-based M_R.In this study, all indices investigated that could be used to replace the FWD-based M_R were also found to be highly correlated to the overall TSD-based structural properties of the pavement and not very highly correlated to the FWD based M_R. Thus, adding a TSD-based measure of the subgrade strength was not recommended at this time. Although the reasons for this lack of correlation between TSD-based and FWD-based subgrade strength measurements are not clear, they likely include unquantified differences in subgrade moisture conditions between measurements from the two devices and also possible limitations of the TSD technology in capturing very small deflections far away from the load application.

An augmented structural condition matrix was used to investigate the effects of incorporating the TSD-based structural condition on the annual mix of pavement rehabilitation treatments recommended and on the resulting average maintenance cost per mile on interstate roads. The approach did not account for the traffic level and pavement age as currently used by VDOT. The treatment categories considered by VDOT are Do Nothing, Preventive Maintenance, Corrective Maintenance, Restorative Maintenance, and Reconstruction. The augmented matrix modifies these treatments based on whether the structural condition is Strong, Fair, or Weak. In general, applying the augmented matrix on the tested interstate network reduced the percentage of the network recommended for Corrective Maintenance and increased the recommended percentages of the other treatments, mainly Preventive Maintenance and Restorative Maintenance, and to a lesser extent the percentages recommended for Do Nothing or Reconstruction.

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