The Emulsion Application Rate (EAR) is critical to the performance of
both tack coats and chip seals. When emulsion is applied to an aged flexible
pavement, a portion of the applied emulsion will be absorbed by the existing
pavement. To compensate, the current practice is to adjust the required target
EAR used in the construction based on visual inspection of the existing
pavement surface, which is subjective.
The objectives of this project are to:
(1) determine the pavement emulsion absorption rate as a function of surface
characteristics and (2) develop guidelines for the adjustment of the target EAR
to account for emulsion absorption based on quantitative measurement of the
existing pavement surface characteristics.
Tack Lifter field experiments conducted on 13
pavements indicate that the absorbed EAR vary considerably depending on the
existing pavement surface conditions.
CR 400 Colorimeter Tack Lifter Components
Statistical analysis of the field
measurements acquired in this study indicate that the application (i.e., chip
seal versus tack coat) and mean texture depth affect the resultant pavement
emulsion absorption rate. A linear regression model was calibrated to predict
the pavement emulsion absorption rate as a function of mean texture depth and
application that yielded moderate prediction accuracy (R2 = 0.56).
The moderate prediction capability indicates that other factors that were not
captured by the application type and texture influence the emulsion absorption
capacity of pavements but allows for an approximation of the absorbed EAR in
cases where project-specific Tack Lifter testing cannot be conducted.
Tack
Lifter experiments conducted on field cores in the laboratory indicate that
Colorimeter measurements of hue are moderately correlated to the pavement
emulsion absorption rate (R2 = 0.42), which merits further
investigation using field experiments in the future. Field core measurements of
emulsion absorption rates indicated differences from field measurements of
emulsion absorption rates with respect to sensitivity to the mean texture depth
and mean values in tack coat applications. This could be due to differences in application
procedures in the field versus the lab. Also, field measurements were made in the wheel path
whereas field cores were extracted elsewhere.
