The curing of asphalt with rubber and its effect on the physical and chemical properties of asphalt-rubber binders

Abstract

The objective of this research was to develop a potentially useful asphalt-rubber binder using the curing process. For the curing process, six parameters, which altered the physical and chemical properties of the asphalt-rubber binder, were tested and evaluated. These variables included asphalt type, rubber type, rubber amount, curing temperature, curing time, and shear rate of mixing. All binders were prepared using two mixing apparatuses. One was set to mix at a low shear rate while the second was set to agitate at a much faster rate. The asphalt-rubber binders were produced using three base asphalts. The rubber used in all experiments were produced by two companies. Two different gradation sizes of one were used while three sizes of the other were used. Experiments were conducted to analyze the physical and chemical properties of each prepared binder. These include the stiffness at low service temperatures, the viscosity measured at various temperatures in and above the rutting region, the solubility characteristics of rubber in asphalt, and the carbonyl area to measure oxidation. Several conclusions were made concerning the curing of asphalt with rubber. It was determined that each asphalt reacts with rubber at different rates. The type and amount of rubber used greatly affected the binder's properties. One company's rubber seemed to outperform the other's. Using rubber with smaller particles produced better results than using rubber with larger gradation sizes. Adding a larger quantity of rubber benefited some properties such as the stiffness at low temperatures and viscosity in the rutting region but worsened the viscosity at temperatures above the rutting region. Increasing the curing temperature seemed to increase the reaction rate between the asphalt and rubber. Extending the curing time benefited the properties of most binders by allowing more rubber to be soluble in asphalt. The higher shear rate increased the asphalt-rubber reaction rate since curing for a shorter time at the faster speed produced similar results as curing for a longer time at a slower speed.