Investigating Effects Of Amine-Based Modifier On Recycled Asphalt Shingles Blending Index

Govinda Sedhay, North Carolina Agricultural and Technical State University


This study was undertaken to investigate the effects of amine-based modifiers on the rheological characteristics of particle-filled viscous media such as recycled asphalt shingles (RAS). RAS are a recycled material that contains high concentrations of asphalt which has the potential for use in hot mix asphalt (HMA) when added to virgin asphalt. When using the RAS as a binder in HMA it is important to mix it with the virgin asphalt properly to achieve the best performance, which can also be enhanced by the incorporation of amine-based modifiers. Tear-off shingles were acquired from a roofing company and ground very fine so that 85% of the particles passed through sieve number 200. The virgin asphalt binder (PG 64-22) and three (20%, 30%, & 40%) percentages of grounded RAS were blended at a temperature of 180°C at a rotational speed of 400 rpm. These three mixtures were then blended with three different amine-based modifiers (1.5% of Rediset®, 0.5% of Evotherm®, and 5% of bio-binder by weight of mixture) at 135oC and a rotational speed of 400 rpm. The percentage of each modifier was selected based on recommendations of the manufacturers. The properties of the blended binder were studied using a rotational viscometer (RV) utilizing a Brookfield Viscometer DVIII-Ultra. Two different spindles were used to measure the viscosity of the binders at four different temperatures (105oC, 120oC, 135oC, and 150oC) and six (5, 10, 20, 25, 50, and 100) different rotational speeds. The analysis showed that viscosity increased with increasing percentages of RAS; however, the viscosities decreased after incorporation of the amine-based modifiers. . Additionally, viscosity results were found to be different between the two spindles used. Viscosity measurement values were consistently higher when the vane spindle was used as compared to the smooth spindle. This can be attributed to incomplete blending of the RAS particles with asphalt matrix. However, the viscosity difference between the two spindles was reduced as the temperature was increased and when modifiers were present. This, in turn, indicates an improvement of blending due to the addition of modifier and an increase in blending temperature. Furthermore, the coefficient of variation was significantly lower in cases where the vane spindle was used, indicating that the vane spindle could be more appropriate for measuring the viscosity of particle-filled viscous media. An empirical relation was proposed to measure the blending behavior of the amine-based modified binders. The blending index was calculated using an empirical relation for all temperatures and rotational speeds. It was found that the blending index was affected by changes in temperature and shear speed. The blending index increased with increasing temperature. In addition, the bio-binder modified binder showed higher blending index compared to the other modified binders. Therefore, bio-binder is effective in reducing binder viscosity and enhancing blending between aged asphalt in RAS and un-aged asphalt (PG 64-22) in the mixture.