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57 C H A P T E R 3 3.1 Summary of EPG Specification Features This research project developed EPG specifications for the selection of asphalt emulsions used in PSTs. The EPG specifications address the critical distresses in chip seal, microsurfacing, and spray seal treatments that are related to binder performance. The EPG specifications grade the emulsions according to the climate and traffic level for which they are appropriate. The key features of the proposed EPG specifications are as follows: ⢠The EPG specifications include fresh emulsion properties that address the stability and constructability of emulsions in PSTs. ⢠The chip seal EPG specifications for residual asphalt binders address low-temperature ravel- ing and bleeding. ⢠The microsurfacing EPG specifications for residual asphalt binders address rutting and thermal cracking. ⢠The EPG specifications define the climatic conditions for which the emulsion can be utilized in PSTs by assigning an EPG temperature that is 3°C higher than the PG temperatures found in the Superpave specifications for asphalt binders in equivalent locations. ⢠The EPG specifications define the traffic conditions (in terms of AADT) for which the emul- sion can be utilized. ⢠Fresh emulsion and residual binder tests in the EPG specifications can effectively capture the materialsâ failure mechanisms that are related to critical mixture performance and can dif- ferentiate binder types. ⢠A temperature-independent relationship was found between the measured binder param- eter and its associated mixture performance measure or each binder test method in the EPG specifications. ⢠Preliminary specification limits are proposed in the EPG specifications based on critical mix- ture performance thresholds. ⢠Short-term validation of the chip seal EPG specifications for specific test temperatures and traffic levels was accomplished by evaluating specially constructed chip seal sections. The microsurfacing EPG specifications could not be validated because existing cracks had propa- gated through the seal shortly after construction and precluded the assessment of binder performance. 3.2 Recommendations for Future Research The following items are recommended for future research: 1. Consideration of the effects of aging in the EPG specifications. The effects of long-term oxidative aging on asphalt emulsion performance are not addressed in the developed EPG Summary and Recommendations for Research
58 Performance-Related Specifications for Emulsified Asphaltic Binders Used in Preservation Surface Treatments specifications. As residual binder undergoes oxidation over the life of the seal, the binder becomes more brittle and susceptible to cracking and raveling. Research is needed to inves- tigate the effects of long-term aging of the residual asphalt binder on the performance of PSTs. If aging is found to be significant, the specifications should be refined to include the effect of aging. 2. Long-term field validation of EPG specifications. Long-term validation of the proposed EPG specifications is needed. This validation could involve in situ field sections and laboratory performance testing. First, asphalt materials are tested and graded for specific climates and traffic levels. Field sections are then constructed in locations nationwide that are appropriate for the specified EPG of the binder and monitored for performance over the design life of these PSTs. If necessary, the EPG specifications will be refined to account for the findings.