Volume 37, Issue 5 (September 2009)
The Influence of Aggregate Interaction and Aging Procedure on Bitumen Aging
Bitumen, like many other organic substances, is affected by the presence of oxygen, ultraviolet radiation, and by changes in temperature. These external influences result in the phenomenon known as “aging” and cause changes in the chemical composition and therefore the rheological and mechanical properties of the bitumen. Aging is primarily associated with the loss of volatile components and oxidation of the bitumen during asphalt mixture production (short-term aging) and progressive oxidation of the in-place material in the field (long-term aging). Both factors cause an increase in viscosity (or stiffness) of the bitumen and consequential stiffening of the asphalt mixture. Aging at moderate levels is generally accepted and can even enhance performance, but at significant levels results in embrittlement of the bitumen, significantly affecting its adhesive characteristics and usually resulting in reduced cracking resistance of the asphalt mixture under repeated loading. It has long been recognized that the characteristics of bitumens are affected by the mineral aggregate with which they come into contact and that age hardening is influenced by both the bitumen and the mineral aggregate as reported by Bell and Sosnovske in 1994. This paper investigates the influence of aggregate type and aging procedure on the rheological and chemical fractional properties of aged bitumen. Asphalt mixtures comprising limestone or granite aggregate have been artificially aged in the laboratory and the rheological properties and chemical composition of the recovered bitumen from the mixtures determined after different durations of aging. In addition, the influence of bulk aging versus thin film aging has been assessed on the same bitumen aged in the presence of aggregate.