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Development of an Improved Design Procedure for Unbonded Concrete Overlays

Status:  Complete
Report Date:  06/09/2020


An unbonded portland cement concrete overlay of concrete pavements (UBOL) is a rehabilitation technique in which the new overlay is isolated from the existing distressed pavement using a separator layer. Typically, a 1-to 2-in asphalt separator layer (or interlayer) is used. Recent innovations in the unbonded overlay technology have led to the adoption of new types of interlayers, such as non-woven geotextile fabric, as well as the use of overlays with joint spacings and layouts that are much shorter than conventional joint spacings. The effect of these design alternatives on the performance of the UBOL cannot be accounted for using currently available design procedures. This report documents the development of a new mechanistic-empirical design procedure for UBOL. It presents the results of laboratory and field studies; the calibration of an advanced structural (Totski) model that better captures the effects of the interlayer and separation between the overlay and the existing pavement; and the development of cracking and faulting performance prediction models for UBOL. The performance prediction models were incorporated into a rudimentary software tool, Pitt UBOL-ME, that can be used for the design and analysis of UBOL. Unlike prior UBOL design procedures, Pitt UBOL-ME can be used to quantify the effect of the performance of the interlayer on the performance of the UBOL and can be used for both conventional and short joint spacings.

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