Asphalt Rubber Chip Seal Project in Texas & the Viscosity Buildup Study of Chemically Modified Crumb Rubber Asphalt (CMCRA)



The chemically modified crumb rubber (CMCR) process for modifying asphalt was developed at the Turner Fair Bank Highway research Center (TFHRC) in 1997. A variant of this process using an additive of 3 weight percent Finaprene 502 in conjunction with CMCR (5%), resulted in a CMCR product which was successfully for the first time for chip seal field application in Texas. This process used AC-5 (5% CMCR) to produce a material meeting the Texas (AC-15-5-TR) for the chip seals. To demonstrate the commercial viability of the process, a scale-up project was conducted at Fina Oil and chemicals facility (Refinery) in Big Spring, TX (Dec., 1999). Fifty-two and one-half tons of modified asphalt (CMCRA) was produced. The material had a viscosity of 3480 cP, a penetration 105 dmm, ductility of 65 cm at 40C, a softening point of 1240F(510C) w/top-bottom delta of 10F. These desirable properties (meeting Texas AC-15-5-TR spec) and resulted because of the favorable interaction of the CMCR system with the asphalt system. Significant viscosity buildup occurred in the new system, which suggests that lower quantities of untreated crumb rubber (CR) can be achieving the desired properties. Tests showed that 40% reduction in additive (CMCR Vs CR) could be used to achieve the same viscosity results. The solubility of CMCRA in TCE (AASHTO T-44-97) came as 98%.

This paper will discuss the CMCRA prepared for Texas field placement and its laboratory data on viscosity, softening point, and ductility comparison of modified asphalt formulation using CMCR.

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