| A curing study was undertaken to determine the effect of asphalt composition, rubber content, rubber mesh size, curing time, curing temperature, and the rate of mixing on asphalt-rubber properties. Curing temperatures of 450, 505 or 533K and either a low-speed mixer or a high-shear mixer were used. The properties studied were rubber dissolution, settling, molecular weight distribution, and low-, intermediate-, and high-temperature rheological properties. Most notable were the variables of curing temperature, rate of mixing, and asphalt composition. Increasing the curing temperature drastically increased the rate of devulcanization and depolymerization of the rubber, while increasing the rate of mixing drastically improved the settling properties of a binder. Lower molecular weight asphalt was better at devulcanizing the rubber, while higher molecular weight asphalt was better at depolymerizing the rubber. These high-cure binders are homogeneous, non-settling, and have a non-detrimental viscosity at hot-mix temperatures, while still being more viscous and elastic at rutting temperatures and less stiff at cold temperatures than the base asphalt.; An aging study was done to determine the effect of rubber content, the degree of curing, and asphalt composition on the oxidation characteristics of asphalt-rubber. Samples were aged under oxygen, nitrogen, or air at temperatures of 333 to 372K. The molecular weight distribution, the carbonyl area, and the intermediate-temperature rheological properties of the samples were measured. Asphalt-rubber did not cure at high-temperature under nitrogen without mixing. When aged under high-pressure oxygen, the reaction mechanism for an asphalt-rubber changed at around 367K. The aging rates for asphalt-rubbers obtained at elevated temperatures and 1 atm air can be used to reasonable extrapolate to the aging rate at road conditions. For asphalt-rubber aged under 1 atm air, the hardening susceptibility was dependent on aging temperature. This finding eliminates the possibility of using high-temperature and 1 atm air aging to extrapolate to the hardening rate at road conditions. The aging index rank obtained by high-temperature aging strongly agreed with the aging index rank obtained by 333K aging. This indicates that high-temperature aging can be used to accurately predict the relative aging performance of asphalt-rubber at road conditions. |
