Trr No. 1323 Materials And Construction, pp. 32-46
A strategic Highway Research Program project-entitled Performance-Related Testing and Measuring of Asphalt Aggregate Interactions and Mixtures-includes development of procedures to age mixtures in the laboratory. Two major effects dominate aging of asphalt-aggregated mixtures : (a) loss of volatile components and oxidation in the construction phase (short-term aging) and (b) progressive oxidation of the in-place mixture in the field (long-term aging). Other factors may contribute to aging. In particular, molecular structuring may occur over a long period of time, resulting in steric hardening. Actinic light, primarily in the ultraviolet range, also has an effect, particularly in desertlike climates. Aging may result in hardening (stiffening) of the mixture, which alters the performance of the mixture. This may be beneficial, because a stiffer mixture will have improved loaddistribution properties and will be more resistant to permanent deformation. However, aging may also result in embrittlement (increased tendency to crack and ravel) and loss of durability in terms of wear resistance and moisture susceptibility. Preliminary tests to evaluate aging methods fpr asphalt-aggregate mixtures have been conducted. Short-term methods include oven aging and extended mixing; long-term methods include oven aging and oxygen enrichment. The effects of temperature level and duration of aging are noted. Test specimens were fabricated from two asphalts and two aggregates, representing extreme property levels. The four mixture combinations were prepared at two levels of permeability representing good and moderate compaction conditions. The effects aging were determined using the diametral resilient modulus test.