Concrete pavement thickness variation assessment with cores and nondestructive testing measurements

Concrete pavement thickness data were collected from sections of two concrete pavements with a nondestructive testing (NDT) device and by measuring concrete core thickness. The NDT device allowed thickness measurements every 15 ft compared with 1,000 ft for each core. Comparison of the core and NDT data showed that core thickness data do not capture the extreme peaks and valleys of pavement thickness variation. Further analysis of the core and NDT thickness data with the Minnesota Department of Transportation's concrete pavement thickness specifications highlighted that contractor pay deductions based on thickness deficiencies were not realized. Autocorrelation analysis of the data showed that concrete pavement thickness variation is not random but is correlated to thicknesses of lag between 30 and 270 ft. This correlation lag is a starting point for answering the question, how often must a thickness measurement be taken to accurately characterize the thickness variation of a concrete pavement?