Relationship between composition and performance of asphalt recycling agents

Abstract

This research was aimed at determining the effects of recycling agent composition on the performance of recycled asphalt with aging. To accomplish this, five experiments were performed, in which blends were produced with controlled compositions, and the performance of these blends was observed during artificial aging. The materials to make the blends were produced using an enlarged version of a commonly used asphalt fractionation procedure. Light supercritical fractions were fractionated into four basic components: asphaltenes, aromatics, oils, and waxes. These materials were used to make blends with controlled amounts of each component, which could be aged alone, or used to recycle aged asphalts. New asphalts were artificially aged for this purpose both by heating with air contact and by using a pressurized oxygen vessel (POV). Experiments were designed and performed in an attempt to isolate the effects of each fraction, and of trace metals, on the behavior of asphalts and recycled asphalts. In each case, the blends produced, and the recycled materials, were artificially aged in a POV for varying lengths of time, and in some cases, at varying temperatures. The results were analyzed in terms of the zero shear, viscosity, and the carbonyl area, a measure of oxidation. It was determined that asphaltenes had a negative effect both on the viscosity and the rate of increase of viscosity, trace metals had no obvious effect, waxes had a negative effect on viscosity, and oils had a positive effect on viscosity and viscosity temperature dependence, but a negative effect on the rate of increase in viscosity. Aromatics were the best materials to use for recycling. The conclusion was that recycling agents should have high aromatic content, little or no asphaltene, low waxes, and controlled amounts of oils for best performance, and that proper recycling agent selection could actually result in improved asphalt aging behavior.