Investigating Binder Flushing of SP-2 Mixes


Introduction: Mix bleeding, or binder flushing, is migration of the bitumen to the surface of the flexible pavement, with or without fines. Krishnan and Rao (1, 2) indicated that migration can htappen by means of two mechanisms: first, by the diffusion of asphalt into the air voids when it is subjected to temperature exceeding its softening point and second by the movement of asphalt due to pressure gradient developed in asphalt. The development of this pressure gradient is due to the reduction of air voids under traffic loads. Both mechanisms can occur simultaneously and the contribution of each depends very much on the temperature-stiffness relationship of the binder, the air voids distribution in the mix and the traffic loads to which the pavement is subjected to. Literature (3, 4) lists mix segregation and binder contamination during the construction process as possible causes of binder flushing.

Objectives: The objective of this study is to analyze available data on early flushing sections of Superpave mixes in Nebraska and to have a better understanding of the possible causes.


Civil, Architectural and Environmental Engineering


Nebraska Department of Roads

Report Number

NDOR Research Project Number P559

Document Type

Report - Technical

Document Version


File Type





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