The emulsion application rate (EAR) is critical to the performance of
both tack coats and chip seals. Typically, only the change in volume of
emulsion in the distributor tank before and after construction is measured for
acceptance, which cannot quantify local variability in the applied EAR. In
addition, the current practice is to adjust the required target EAR to account
for absorption into the existing pavement based on visual inspection, which is
subjective. This study identifies suitable test frameworks for in-situ
measurements of EARs, leveraging the results of FHWA/NCDOT 2014-03. In
FHWA/NCDOT 2014-03, the Tack Lifter was proposed as a practical means to obtain
in-situ EAR measurements.
The results of this study demonstrate that in tack
coat projects, measurements of the applied EAR can be made by simply placing
pre-weighed plates on the roadway prior to emulsion application. The net mass of
the plate after emulsion application is used to determine the applied EAR. In
chip seal projects, the applied EAR can be measured by performing Tack Lifter
tests on impermeable plates placed in the roadway prior to emulsion
application. The Tack Lifter uses an absorbent sheet that is pressed onto the
application surface with a weighted device to obtain spot checks of EARs. By
conducting Tack Lifter tests directly on the pavement, the “effective” EAR
(i.e., the amount of emulsion available after absorption) can be measured in
both tack coats and chip seals; this can better inform target EAR selection.
Residual binder rates can be obtained by collecting pre-weighed plates or Tack
Lifter sheets in-situ and weighing after curing; this mitigates time
constraints and the need for leveling and shielding a balance from wind in the
field. Training tools for the NCDOT, including guidelines, videos, and draft
AASHTO standard practices were developed to facilitate implementation into
practice.
