Published: 2007-04-01

Evaluation of effectiveness of use of FWD for assessment of pavement interlayer bond

Dariusz Sybilski , Tomasz Mechowski , Przemysław Harasim


Interlayer bonding is one of the most important factors influencing proper asphalt pavement performance, to a large extent underestimated until recently. Interaction of layers in pavement structure depends on interlayer bonding, and it influence pavement durability. Lack of or weak interlayer bond cause that layers do not interlock and pavement load is not properly transferred from upper layer to lower layer. It results in higher stresses at bottom of upper layer and higher strains in unbounded base. Life of pavement may be shorter by up to 40 - 70 %. Deterioration of road pavement due to insufficient interlayer bond is known for years, testing of this pavement property was undertaken only some 20 years ago. Interlayer bond between two asphalt layers is derived from two main factors: the first − gluing both layers with bituminous binders being constituents of both layers or with intentionally applied tack coat, and the second − interlocking of mineral grains of both layers. This paper presents the trial to develop testing procedure with use of FWD (Falling Weight Deflectomer). The procedure shall allow estimation of interlayer bond in the real pavement on the basis of interpretation of FWD measured pavement deflections. For qualitative evaluation of the observed phenomenon, the Interlayer Bond Index is proposed. On the basis of relatively wide field and laboratory tests the recommendations for limits of Interlayer Bond Index were proposed.

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Sybilski, D., Mechowski, T., & Harasim, P. (2007). Evaluation of effectiveness of use of FWD for assessment of pavement interlayer bond. Roads and Bridges - Drogi I Mosty, 6(2), 41–83. Retrieved from

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