Improved Backcalculation Procedure for Continuously Reinforced Concrete Pavement

Abstract

Falling weight deflectometer (FWD) testing is effective in evaluating the structural response of in-situ concrete pavements through the backcalculated pavement layer parameters. Specifically, the FWD data can be used to backcalculate the foundation layer and concrete stiffness or the soil layer stiffness, effective slab thickness, and slab–base interface condition. Since continuously reinforced concrete pavement (CRCP) has closely spaced transverse cracks, the traditional backcalculation assumption of an infinite slab can lead to significant errors in the backcalculated results. In this paper, solutions for backcalculated modulus of subgrade reaction ( k-value), elastic modulus of concrete ( E), and effective thickness ( heff) for different crack spacing have been derived from 2-D finite element analysis. AASHTO sensor configuration (0, 12, 24, 36 in.) was recommended for CRCP with crack spacing ≥6 ft, and an alternative solution for crack spacing of 4 and 5 ft was proposed with AREA24. Crack load transfer efficiency (LTE) across transverse cracks had limited impact on backcalculated results if the LTE was >80%. As expected, the backcalulation values were sensitive to the load plate’s longitudinal position relative to the transverse crack especially for crack spacings smaller than 8 ft. The proposed backcalculation method was applied to a field CRCP test section with different crack spacing, reinforcement ratio, and base types.