Journal of Materials in Civil Engineering, August 1996 v8 n3 
            p153(4) 
                Viscosity characteristics of rubber-modified asphalts. T.J. 
                Lougheed; A.T. Papagiannakis. 
            Author's Abstract: COPYRIGHT 1996 American Society of Civil 
            Engineers 
            This study presents a state-of-the-art review of crumb-rubber 
            modified (CRM) asphalt concrete technology and describes the results 
            of viscosity measurements of CRM asphalt cements using a Brookfield 
            viscometer. Literature was reviewed in relation to both the wet 
            process (i.e., mixing of the crumb rubber with the binder prior to 
            mixing with the aggregate) and the dry process (i.e., simultaneous 
            mixing of the crumb rubber, the binder, and the aggregate). In wet 
            processes, the reaction that takes place between rubber particles 
            and asphalt binder is not chemical in nature, but rather a diffusion 
            of the light aromatic components of the binder into the crumb 
            rubber. This results in a reduction in the viscosity of the binder, 
            which depends on the type of the binder, the type of the rubber, the 
            mixing temperature, and the mixing energy (i.e., time). In dry 
            processes, the crumb-rubber particles replace aggregate particles in 
            the asphalt concrete mix, while due to the limited mixing time 
            allowed, no significant reaction takes place between the crumb 
            rubber and the binder. Brookfield viscometer testing of the CRM 
            binder was conducted following a variation of the ASTM standards 
            D2196-86 and D4402-87. Three binders were tested, namely AC-5, 
            AC-10, and AC-20, with CRM percentages of 0%, 3%, 5%, 7%, 12%, and 
            18%. The CRM particle size was finer than sieve size No. 80. The 
            viscosity of the CRM asphalt cement initially decreased in time, 
            until the temperature of the crumb-rubber chips reached that of the 
            binder. This took place in approximately 30-40 min, when a minimum 
            viscosity value was reached, called the "stabilized" 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. 
             
             Article A18627474