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Characterization of asphalt cements modified with crumbed rubber from discarded tires : final report.
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1994-11-01
[PDF-1.82 MB]
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Alternative Title:Characterization of asphalt cements modified with crumbed rubber from discarded tires.
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Abstract:The potential legislative requirement for incorporation of scrap rubber into asphalt blends mandated a thorough evaluation of the influence of scrap rubber additives on the physical properties and aging characteristics of rubber/asphalt blends. Blends with up to 20% ground vulcanized rubber (both crumb and 200 mesh powder particles) from recycled tires were prepared with asphalt cements of various grades (AC5-AC30) and evaluated using DMA. Blends produced from powdered rubber particles exhibited Newtonian behavior at high temperatures; similar behavior was not observed with crumb rubber blends. The mechanical properties of asphalt-rubber blends depend upon the concentration of rubber additives, the particle dimensions, and the chemical composition of the asphalt. Some asphalts induced excessive swelling of the rubber particles, resulting in 135C viscosities greater than SHRP recommended 3 PaSec. The dynamic mechanical characteristics of all blends are discussed in terms of G*sin & and G”; comparative data is presented according to the new SHRP binder specifications. Constant stress creep and creep recovery of the polymer or rubber asphalt blends proved to be a sensitive measure of the additive content.
Pressure aging vessel (PAV) aging of the asphalt-rubber blends revealed a significant difference between crumb rubber and powdered rubber additives. Simple blends of crumb rubber with asphalts ranging in grade from AC5 to AC30 exhibited phase separation during a thin-film oven aging test. In contrast, blends with powdered rubber appeared to remain compatible or at least partially compatible through the PAV process, and the blends retained the physical properties associated with the additive. The DMA data suggest that the low-temperature cracking resistance of asphalt—powdered rubber blends is enhanced.
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