As with the previous two symposia, the 32 papers from the June/July, 1999, Seattle symposium present advances in the nondestructive testing of pavements using conventional falling weight deflectometer techniques and other promising techniques such as ground penetrating radar, rolling weight deflecto

This study utilized Illinois DOT (IDOT) mechanistic-empirical (M-E) technology and Mn/ROAD mainline pavement section data and information to verify/refine/modify IDOT M-E analysis and design concepts and procedures for full-depth asphalt concrete (FDAC) and conventional flexible pavements (CFP). The Mn/ROAD mainline flexible pavements include eleven CFP and three FDAC pavement sections. Four different granular materials were used in the conventional flexible pavements. A fine-grained soil subgrade (R-value of about 12) is present throughout the mainline. Laboratory material testing results, field distress measurements, and FWD test data were used to study pavement deflection response and performance (rutting and asphalt concrete fatigue). The study demonstrated that the IDOT M-E analysis and design procedures for FDAC and CFP sections are adequate. The ILLI-PA VE structural model adequately predicts the pavement responses. The use of bi-linear (arithmetic) subgrade model and the "theta" granular material model ILLI-PA VE inputs closely replicate CFP field FWD deflection responses. The effect of granular material quality on CFP deflection response is very limited. The ILLI-PAVE FWD backcalculation algorithms are adequate for estimating the moduli of asphalt concrete and sub grade soils.

This study utilized I DOT mechanistic-empirical (M-E) procedures and Mn/ROAD low-volume road (LVR) data and information to verify/refine/modify analysis and design concepts and procedures for L VR flexible pavements. The Mn/ROAD L VR flexible pavements include conventional flexible, full-depth asphalt, surface-treatment and aggregate-surface sections. Laboratory test results, field distress measurements, and FWD test data were used to study the affect of granular material quality on pavement performance and deflection response. The results from the rapid shear tests, permanent deformation tests and field rutting measurements show that granular material rutting potential can be characterized by a rapid shear triaxial test at 15-psi confining pressure. For conventional flexible pavements, granular material quality did not affect the pavement deflection response, but material quality effects were significant for aggregate-surface and surface-treatment pavements. ILLI-PAVE predicted pavement responses were fairly accurate for sections with thicker asphalt concrete surfaces. The FWD deflection basin parameter AUPP (Area Under Pavement Profile) can be used to predict the strains at the bottom of AC layer. Effect of subgrade type on pavement response and performance was studied. Sandy subgrades showed little or no change in pavement structural response due to spring-thaw effects. For the cohesive subgrade sections, moisture changes and spring-thaw effects increased surface deflections. The study showed that the lOOT LVR flexible pavement mechanistic-empirical design concepts and procedures are valid and adequate.

This report presents the results of an evaluation process of several different flexible pavement backcalculation programs. The objective of this study was to compare the performance of the candidate programs in terms of useability and accuracy of backcalculation results. This was accomplished by evaluating the selected programs using both field and simulated data. The results of the analysis were used as the basis for selecting a program for routine analysis of Mn/ROAD pavement deflection data. In situ pavement strains were measured during falling-weight deflectometer tests. The measured strains were then compared to backcalculated strain values from each program. In addition to the field tests, a series of hypothetical pavement structures with a range of prescribed layer thicknesses and moduli were analyzed to obtain surface deflection data. These surface deflections were then used as input for each program involved in the study. The output from each program was compared to the expected values.

This publication provides a guide to the Minnesota Department of Transportation's current research activities.