William King Jr

Effects of Curing Time, Temperature, and Vacuum Pressure on Asphalt Emulsion Residue Recovered by Vacuum Drying Method

This study included five different recovery methods for six emulsions (CRS-2, CRS-2P, CRS-2L, SS-1, SS-1L, and SS-1H) and their corresponding unaged base binders. These five recovery methods consisted of different curing times, temperatures, and vacuum pressures. The goal of this study was to understand the effect of these variables on the rheological properties of the recovered asphalt emulsion residue during the recovery process. Rheological properties such as G*/sin δ, phase angle, and average percent strain recovery were determined to quantify stiffness, oxidative aging, and change in creep recovery due to polymer modification. One new recovery method using a vacuum drying oven was explored in this study. This method reduced the effects of oxidative aging and reduced the recovery time to 6 h. The results show that this newly proposed vacuum drying method ensured better drying of the sample and produced residue that was not unnecessarily aged and was similar to unaged base binder in stiffness, whereas with ASTM D7497 oxidative aging plays a significant role in residue stiffness by almost doubling the stiffness relative to unaged base binder. Also, this 6-h vacuum drying method allowed us to clearly identify the presence of polymer. Overall, this report explains the reasons for the differences between the stiffnesses of unaged base binder and emulsion residue, considering oxidative aging, remaining moisture, emulsifier, and polymer modification.

Characterization of Recycled Asphalt Shingles

While the recycling of asphalt shingles is beneficial in reducing the consumption of virgin materials, road performance should not be compromised. One major concern with recycled asphalt shingles (RAS) relates to the variability in the properties of the recycled materials originating from different sources. In addition, the rheological properties of RAS have not been evaluated as well as its influence on the virgin binder when used in asphalt mixtures. Therefore, the objectives of this study were to characterize the rheological properties and molecular fractions of RAS materials sampled from different sources across the country. In addition, the influence of RAS on the Superpave performance grade (PG) of the binder in the mix was investigated. Results of the experimental program indicated that the asphalt cement (AC) content in tear-off shingles was consistent among different RAS sources across the country. However, AC content in manufacturer waste shingles was noticeably lower than in tear-off shingles. In addition, all extracted RAS binders were graded as PG 118 + - xx using the Superpave binder specification system. This stiff behavior is due to the binder used in shingle manufacturing, which is an air-blown asphalt binder with stiff characteristics and low elongation properties. Results showed that at a RAS content of up to 5%, the high temperature grade of the blends was increased by one to seven grades and the low temperature grade was reduced by one grade. The use of binder blending charts is recommended to account for the influence of RAS in the mix design. At a RAS content of 10%, the binder blends did not pass the Superpave criterion at low temperature.