Evaluation of PCC joint stiffnesses using LTPP data

Shear stiffness of joints and cracks profoundly affects the performance of concrete pavements. This paper presents a systematic analysis of stiffnesses of joints in jointed concrete pavements (JCP) and cracks of continuously reinforced pavements (CRCP) using deflection data collected under the Long Term Pavement Performance (LTPP) program. To estimate joint behavior, representative load transfer efficiency (LTE) indexes were calculated for all LTPP sections and a trend analysis was performed to evaluate the effect of Falling Weight Deflectometer (FWD) load level on LTE. It was found that the majority of the joints did not show significant load-level dependency. This justifies use of a simple Tabatabae-Barenberg (TB) model for routine pavement analysis. The paper also discusses a backcalculation procedure for determination of TB model parameters. Joint stiffnesses were backcalculated from LTEs, coefficients of subgrade reactions, and radii of relative stiffness. As expected, it was found that cracks in CRCP usually have higher stiffnesses than joints of JCP, while non-doweled joints usually have much lower stiffness than doweled joints. It was also found that joint stiffness could vary significantly during the day.