ABSTRACT
ABSTRACT: This paper deals with the chemical characterization of bitumen which was part of the rheological and chemical investigations into the effect of aging on the binder properties of Porous Asphalt Concrete (PAC). Analytical methods such as Infrared spectroscopy (FTIR) and Gel-permeation chromatography (GPC) are effective tools to assess the chemical changes in bitumen. These methods were adopted to investigate the effect of bitumen aging on the molecular structure (Molecular Weight distribution, MWD) and the functional groups responsible for oxidation/aging of laboratory aged and field binders. The test results show that aging increases the large molecular seize portion in the binder molecular distribution due to the formation of oxidation products-Ketones (C=Ο) and sulphoxides (S=Ο). Laboratory aging of bitumen using a standard aging method and PAC mixture aging under a proposed new aging protocol that combines temperature, UV light, and humidity were employed to simulate the field aging of PAC. Prediction based on the kinetic approach with the use of the characteristic peak areas of oxidation products in the IR spectrum shows that the field aging of PA is much more severe than the lab bitumen aging. The standard long term lab bitumen aging was found to be not satisfactory in predicting field aging of PAC. Although only 2.1 years of field aging could be predicted, the proposed lab mixture aging protocol showed similar aging behaviour as the field aging. An improved mixture aging protocol is suggested in order to better simulate the binder aging in reality.
