Quantifying the benefits of improved rolling of chip seals : final report, June 2008.

This report presents an improvement in the rolling protocol for chip seals based on an evaluation of aggregate
retention performance and aggregate embedment depth. The flip-over test (FOT), Vialit test, modified sand circle
test, digital image processing technique, and the third-scale Model Mobile Loading Simulator (MMLS3) are
employed to evaluate the effects of the various rolling parameters and to measure chip seal performance. The
samples used to evaluate the chip seal rolling protocol were obtained directly from field construction. In order to
determine the optimal rolling protocol, the effects of roller type, number of coverages, coverage distribution on the
sublayers of a multiple chip seal (i.e., the split seal and triple seal), and rolling pattern are evaluated using the results
of aggregate retention performance tests, the modified sand circle method, and the digital image process. It is found
that two types of roller, the pneumatic tire roller and the combination roller, are recommended as the optimal rollers
for the chip seal. In addition, it is found that the optimal number of coverages for the chip seal is three coverages.
Moreover, the performance of the triple seal without coverage at the bottom layer does not affect the aggregate
retention performance, although the split seal does require coverage at the bottom layer. Finally, it is found from the
MMLS3 results that the delayed rolling time between the spreading of the aggregate and the initial rolling
significantly affects the aggregate loss, and that the delayed rolling time is related to the aggregate moisture
condition and the ambient temperature. Effects of different rolling patterns are investigated based on the delayed
rolling time and roller speeds, and recommendations are developed for two- and three-roller scenarios.