The effect of aging techniques on asphalt low-temperature properties

Abstract

This study includes three phases wherein the effects of various aging techniques on asphalt low-temperature properties were investigated. In addition, two other studies were conducted: air-blowing was investigated as a possible long-term aging test and modifier performance was compared with respect to aging. In Phase I of this study it was shown that 38 days of aging at 60°C and 1 atmosphere of air is approximately equivalent to 20 hours in the PAV at 100°C after both have been RTFOT-aged. Low-temperature properties of the samples were found not to vary significantly between the PAV and environmental room aged material. In Phase II of this work, a correlation was developed from the high-temperature parameter G*/sin[(ð)] at 58°C and 10 rad/s to correct the low-temperature performance grade when one desires to skip the long-term aging procedure. The correlation proved to give a maximum error of ±1.6°C for the low-temperature performance grade and a percent error of ±6.4%. In Phase III of this study it was shown that as asphalts are aged for extended periods their relative ranks with respect to SHRP low-temperature specifications change. This indicates that the SHRP long-term aging specifications result in an arbitrary ranking of asphalts with respect to low-temperature properties. Air-blowing was investigated as a possible alternative for long-term aging in this study. Upon examining the data obtained by long-term air blowing, it was concluded that air-blowing is not a suitable long-term test because it did not consistently produce samples comparable to those aged in the environmental room. To summarize the work in comparing various modifiers, the higher weight percent modified samples showed considerably better low-temperature properties. The 18% RSGF-20 modified sample showed the best improvement to low-temperature properties followed by 4% SBS and 4% SBR. For high-temperature properties 4% SBS proved to be the best modifier, followed by 4% SBR. Polymer modifiers, therefore, should be used in concentrations of at least 4% by weight, where SBS rather than SBR is recommended. If ground tire rubber is used, a high cure process with 18% by weight rubber provides excellent benefit for both high and low-temperature properties.