The industrial manufacture of tire rubber-modified asphalts with enhanced rheological performance and improved longevity

Asphalt binders have a viscosity-temperature susceptibility causing their operating properties to vary, and the binder is subjected to viscosity hardening through oxidation. Compositional properties and additives influence physical properties. The use of polymers and ground tire rubber as binder modifiers is known to reduce the temperature susceptibility. Virgin polymers are expensive, while used automobile tires contain a substantial amount of useful polymer material and are a waste commodity. This dissertation is a study of the production and performance of tire rubber modified asphalt binders.; My first study was an evaluation of the rheological performance of modified materials. A number of blending schemes were evaluated. The use of tire rubber reduces the viscosity-temperature susceptibility of the binder. Warm-weather rutting and cold-weather cracking are reduced. High-shear mixers at elevated temperatures yielded a more homogeneous product.; By far the most predominant cause of road-binder failure is fatigue cracking, caused by oxidative hardening. Certain asphalt compounds (asphaltenes) are polar to the degree that they are mutually attractive, forming large viscosity-building structures. Oxidative aging increases the polarity of asphalt compounds, increasing the fractional content that contributes to viscosity. Aging simulations of asphalts containing tire rubber were performed. It was found that rates of viscosity hardening were reduced by up to 30 percent; the added cost of obtaining and incorporating tire rubber could be offset by increased pavement life. A model was developed to interpret the tire rubber structures present in the binder and how they relate to such asphalt components as asphaltenes. The model integrates blending techniques, degree of homogeneity, and aging properties.; Finally, the use of laboratory equipment to simulate an industrial process was examined. The laboratory process utilized a 2.0- to 2.2-kg batch that was mixed for 2.5 to 6.5 hours at various temperature and rpm settings. The lab technique was compared to appropriate industrial processing equipment, a colloid mill. The objective was to predict the aspects of storage separation and installation, using a rapid rheological test. This test allows an industrial site to examine the quality and gauge the progress of its process in real time, rather than employ a cookbook approach.