United States Department of Transportation
i
Investigation of the Impact of Milling and Construction on the Bond Strength of Remaining Thin (Scab) Layers
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2022-11-01
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[PDF-11.65 MB]
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Abstract:Field investigation in Florida indicated that there was a potential link between weakly-bonded scabbed areas and slippage failure in the braking zones. Also, evidence from NCAT test track studies suggested that localized interface debonding might lead to surface cracking under free-rolling traffic. The primary objective of this research was to determine critical responses and potential distress in asphalt overlay with scabbing. To achieve the objective, both conventional analysis assuming a global interface representation and finite element analysis with a hybrid interface representation were conducted to evaluate the effect of weakly-bonded scabbed layer on pavement responses and potential distress. Furthermore, impact analysis was performed to investigate whether compaction of overlay would weaken the bond below the scabbed layer. This research revealed that under the free-rolling condition, the presence of weakly-bonded scabbed area has the potential to cause near-surface cracking initiated at the upper interface for intermediate and large size scabs, and reflective cracking at the lower interface and further interface debonding at the edge of the scab for intermediate size scab. Under the braking condition, the presence of poorly-bonded scabbed area would most likely cause slippage at the overlay surface for intermediate and large size scabs. It would increase the potential of further interface debonding for intermediate size scab. Also, it would increase the potential of near-surface cracking and reflective cracking regardless of scab size. Roller compaction would likely weaken the bond below the scabbed area. Vibratory rollers would induce more critical conditions than oscillatory rollers. Therefore, the following guidelines are provided for dealing with scabbed sections: i) Make every effort to set the milling depth to minimize scabbing during resurfacing; ii) Loose scabbing should be removed prior to resurfacing; and iii) Consider removing isolated scabbed areas or scabbed areas adjacent to critical locations such as intersections and other braking areas.
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