Viscosity Characteristics of Rubber-Modified Asphalts

Abstract

The authors of this investigation present a state-of-the-art review of crumb-rubber modified (CRM) asphalt concrete technology and explain the results of viscosity measurements of CRM asphalt cements using a Brookfield viscometer. Literature was reviewed for both the wet process and the dry process. The reaction in the wet process that occurs between rubber particles and asphalt binder is not chemical in nature, but a diffusion of the light aromatic components of the binder into the crumb rubber. The result is a reduction in the vicosity of the binder, which depends on the type of the binder, the type of the rubber, the mixing temperature, and the mixing energy. The crumb-rubber particles in the dry process replace aggregate particles in the asphalt concrete mix, while due to the limited mixing time permitted, no significant reaction occurs between the crumb rubber and the binder. Brookfield viscometer testing of the CRM binder was performed following a variation of the American Society for Testing and Materials (ASTM) standards D2196-86 and D4402-87. Three binders with CRM percentages of 0, 3, 5, 7, 12, and 18 were tested. The CRM particle size was finer than sieve size Number 80. The viscosity of the CRM asphalt cement initially decreased in time, until the temperature of the crumb-rubbber chips reached that of the binder. This occurred in about 30 to 40 minutes, when a minimum viscosity value was reached called the viscosity. The high-percentage CRM, however, experienced a linear increase in viscosity with time at a rate of approximately 180 cP/hr as mixing continued past the stabilized viscosity.