United States Department of Transportation
i
Development of laboratory mix design procedures for RAP mixes.
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2013-12-01
[PDF-581.34 KB]
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Abstract:The objective of this study was to evaluate the amount of blending that occurs between RAP and virgin asphalt
binders in plant produced HMA in which RAP is incorporated. This objective was accomplished by testing plant
produced mixture from three different on-going HMA projects. Two of the three projects incorporated 15 percent
RAP while the third project incorporated 30 percent. Samples were brought back to the laboratory and subjected
to a staged extraction/recovery process. Asphalt binder recovered from each stage was subjected to Dynamic
Shear Rheometer testing in order to determine the high failure temperature using a criterion of 2.20 kPa.
Based upon the research approach, it was concluded that majority of asphalt binder was extracted and recovered
from the first stage of washing. The amount of asphalt binder extracted/recovered from successive washes
decreased, except for the last stage. For mixes containing 15 percent RAP, the asphalt binder was not significantly
affected by the RAP though there was a slight increase in failure temperature through the staged washes, except
for the last stage. The majority of the asphalt binder from the 30 percent RAP mixture was removed during the
first stage of washing. The stiffness of the asphalt binder after Wash 1 was higher for this 30 percent RAP mix
than for the 15 percent RAP mix; however, the increase in stiffness was not large. The increase in stiffness for
successive washes was higher for the 30 percent RAP mix than for the 15 percent RAP mixes. Based upon these
findings, it was concluded that partial blending between RAP and virgin asphalt binders when RAP is
incorporated into plant produced HMA.
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