Field and Laboratory Evaluation of Environmental Effects on Chip Seal Performance: Freeze-Thaw and Asphalt Aging

摘要

Chip seals generally deteriorate as a result of asphalt oxidation, wear and polishing of aggregates, bleeding, and raveling (loss of aggregates). In this study, two major environmental effects on chip seal performance, freeze-thaw, and asphalt aging were investigated based on laboratory tests and field distress survey. For freeze-thaw evaluation, laboratory chip seal samples were prepared for 18 combinations (6 aggregates X 3 asphaltic materials). A simple freeze-thaw protocol was developed and evaluation of freeze-thaw effect on aggregate types reveals that both the precoated and uncoated expanded shale lightweight aggregates perform comparatively very well against freeze-thaw. Evaluation of freeze-thaw effect on asphaltic material types reveals that CRS-2P, an emulsion performs significantly better than hot asphalts, namely PAC-15 and AC20-5TR. For aging evaluation, asphaltic materials were extracted from 15 (5 aggregates X 3 asphaltic materials) field test sections and increase in stiffness due to aging were determined using a dynamic shear rheometer. For each of the five aggregates, CRS-2P shows the lowest G~*/ sinδ, indicating minimum field aging susceptibility among the three asphaltic materials while AC20-5TR shows slightly higher G~*/sinδ than PAC-15, indicating maximum field aging susceptibility. Overall field distress ratings of the CRS-2P sections (sum of distress ratings of all the CRS-2P sections) are better than those of PAC-15 and AC2O-5TR. The overall distress ratings of PAC-15 sections are better than overall distress ratings of AC20-5TR. In case of aggregate types, precoated expanded shale lightweight test sections performed the best, while expanded clay lightweight sections performed very poorly. Both freeze-thaw and asphalt aging tests closely reflect field performances and it can be concluded that the freeze-thaw and aging performances can be used as effective tools for predicting long term chip seal performances.