On the TSD deflection velocity measurements: a revision to the current state of the art and discussion over its applicability for concrete pavement assessment

The fourth-generation TSD can provide pavement deflection data at a much higher rate than previous versions. This data is valuable to evaluate the structural health of the transverse joints in concrete pavements. Analysis of TSD measurements from a jointed pavement segment allowed the detection of a mistake in the way the TSD's deflection velocity [v(y)] data is processed to get deflection slope [S] estimates: We state and prove that the well-known direct relationship between v(y) and S is only valid in limited scenarios, and particularly invalid nearby the transverse joints. We highlight that v(y) is made up of two components, one of which is related to S and that at the vicinity of a discontinuity in the pavement structure, the second component of v(y) gains relevance and explains the discrepancy between v(y) and S. Also, it is shown that TSD v(y) measurements gathered near a joint resemble v(y) signals simulated with a linear elastic model. Thus, this study brings new insight into the contents of a TSD v(y) measurement and buttresses the TSD's reliability as a v(y) measurement device. Plus, it suggests that further research should develop TSD data interpretation schemes based on v(y) instead of deflection slopes and depths.