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Asphalt cement binders have two different long term characteristics when they are used in the pavement. The first characteristic is viscoelastic, in which the binder undergoes a reduction in the stiffness and strength properties under loading for a long period of time. This characteristic is also accompanied by an increase in the deformation with time, even under a tolerable amount of loading, or the so called creep properties. The second characteristic is the age hardening, in which the asphalt cement displays changes in the stiffness properties with time caused by the hardening of the asphalt binder under weathering, oxidation and other environmental actions.
These two long term characteristics were investigated and compared for typical paving mixtures. The viscoelastic behaviour was investigated by studying the change in the asphalt mix modulus at different levels of loading rate and testing temperature. The age hardening behaviour was evaluated by studying the effect of artificial weathering on the resilient modulus, indirect tensile strength and failure deformation of laboratory compacted cores.
Laboratory compacted specimens displayed higher stiffness and lower failure strains at higher loading rates and/or low temperatures. Laboratory simulated age hardening caused all compacted mixtures to develop a gain in stiffness and strength properties. This gain, however, was associated with brittleness and failure at low deformation levels.
Asphalt Cement, Long Term Performance, Viscoelasticity, Aging, Loading Rate
UNDP Advisor, Ministry of Communications, Riyadh,