Production of Asphalt-Rubber Binders by High-Cure Conditions
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A curing study was undertaken to determine the effect that asphalt composition, rubber content, rubber mesh size, curing time, curing temperature, and rate of mixing have on asphalt-rubber properties. Curing temperatures of 232C or 260C (450F or 500F) and a high-shear laboratory mixer were used to produce the asphalt-rubber blends. The properties studied were rubber dissolution; rubber settling; molecular weight distribution; and low-, intermediate-, and high-temperature rheological properties. Increasing the curing temperature from 232C to 260C (450F to 500F) drastically increased the rate of devulcanization and depolymerization of the rubber, whereas increasing the rate of mixing from 4,000 rpm to 8,000 rpm drastically decreased the settling rate of rubber in a binder. Lower-molecular-weight asphalts were better at devulcanizing the rubber; higher-molecular-weight asphalts were better at depolymerizing the rubber. These high-cure binders are homogeneous in appearance and slow to phase separate on standing; they have acceptable compaction viscosities at hot-mix temperatures, higher G*/sin at rutting temperatures, and lower stiffness at cold temperatures than does the base asphalt.
