Quantifying the Benefits of Improved Rolling of Chip Seals.

Abstract

This dissertation 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, as determined from measurements of the aggregate, 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 that the rolling pattern is strongly related to a delayed rolling time between the aggregate spreader and the initial rolling time. Therefore, it was recommended that two pneumatic tire rollers applied initial one coverage with optimal delayed rolling time (between 2 min. and 4 min.) to entire lane width, and then the combination roller applied two additional coverages. Further, it is confirmed that the delayed rolling time is related to the aggregate moisture condition and the ambient temperature.