Backcalculation Procedure for Bonded Concrete Overlays of Asphalt Pavement

Abstract

Bonded concrete overlays of asphalt (BCOA), previously known as ultra-thin whitetopping, have become increasingly common in Illinois in the past 15 years. No methods exist for assessing in situ properties under loading for this type of overlay. A procedure to backcalculate layer properties from falling weight deflectometer tests does exist for concrete slabs on grade with infinite dimensions, but this method is not applicable to finite-sized BCOA slabs with multiple layers and interfaces. Based on two-dimensional finite element modeling of BCOA pavements, a backcalculation procedure was derived for a range of expected slab sizes, effective concrete pavement thicknesses, joint load transfer efficiencies, and foundation layer stiffnesses. The backcalculated effective concrete thickness quantifies the load-carrying capacity of the BCOA pavement, variation of the structural capacity as a function of distance along the roadway, and potentially the condition of the concrete–asphalt bond interface and the underlying asphalt concrete layer. Application of the BCOA backcalculation procedure to falling weight deflectometer data collected from several projects in Illinois confirmed the reasonableness of the procedure through observed performance and estimated layer thicknesses from construction.

Evaluation of Bonded Concrete Overlay of Asphalt under Accelerated Loading

“…FWD tests were performed at different chainage stations along the BCOA pavement test section before and after the APT testing. FWD deflection results were used to characterize the in-situ structural capacity of the BCOA pavement test sections using the method proposed by King, D. and Roesler, J.R. ( 1 ). Considering the BCOA finite slab size, varying load transfer, and PCC-asphalt interface bond condition, this method helped to backcalculate the effective slab thickness (heff) and subgrade reaction (k) to provide an estimated structural capacity of the BCOA test sections.…”

“…Typically, the distressed AC pavement is milled and cleaned which helps to create a bond between the AC layer and the concrete overlay. The bonded layers promote the composite action of the pavement section, benefiting from the structural capacity of the existing AC layer (1)(2)(3)(4). Additionally, a short joint spacing is typically used, which reduces the flexural and curling stresses of the overlay and the debonding of the concrete and the asphalt at early ages (5).…”

Untitled

“…The evaluation of asphalt reinforcement on flexible pavements using the FWD follows a methodology proposed in the AASHTO 93 guide. Still, the mounts on a mixed pavement (concrete slab with asphalt overlay) as is the case of the Central Highway from km 12+250 to km 26+500 would not be possible to apply directly due to the type of rigid structure, so a methodology is proposed to determine the Structural Number from the back-calculation parameters for the model of a rigid pavement (King & Roesler, 2014).…”

Improved Backcalculation Procedure for Continuously Reinforced Concrete Pavement

“…Unfortunately, the study primarily focused on JPCP and did not cover a sufficient range to include all expected L / ℓ for all types of concrete pavements. King and Roesler proposed a backcalculation procedure for the bonded concrete overlays of asphalt pavement system based on smaller panel sizes, with a smaller slab length to radius of relative stiffness ratio ( L / ℓ ) ranging from 1.1 to 5.3 given a slab aspect ratio of one ( 11 ). Ironically, no study has been found in the literature justifying backcalculation of CRCP layer properties or effective thickness with infinite slab equations.…”

“…Ironically, no study has been found in the literature justifying backcalculation of CRCP layer properties or effective thickness with infinite slab equations. Furthermore, existing finite-sized slab solutions ( 10,11 ) will not directly work for CRCP because of their larger slab aspect ratios, for example, 0.25–1.0.…”