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Effect of F-T Wax on aging characteristics of warm mix asphalt binders

Details zur Publikation
Simnofske, D.; Mollenhauer, K.
International Journal of Advance Research in Science and Engineering
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Zusammenfassung, Abstract
The use of rheology modifying additives in asphalt mixes for reducing the mix production temperature and/or increasing the reliability of the compaction process in order to obtain durable pavements, is state of the art. F-T wax decreases the viscosity of bitumen and imparts lubricity above its melting temperature range, resulting in improved workability and compactibility of the asphalt mixes. The wax is thoroughly mixed with the bitumen which poses the question of influencing physico-chemical properties of the binder, such as aging properties. In order to evaluate the potential effects on aging, three bitumen samples were prepared in the laboratory: a bitumen 50/70 as control sample and the 50/70 mixed with two F-T waxes of different chemical composition. The binders were evaluated in the fresh state as well as short-term aged (by RTFOT) and long-term aged (by PAV) states respectively. Besides effects on mechanical/rheological properties, the main focus was the detection of ageing effects on the chemical and colloidal composition of the binders. For the rheological characterization, complex shear modulus tests were conducted in a temperature range of 20 °C to 90 °C. The compositions of the binders in terms of major chemical groups were evaluated by IR spectroscopy and by performing SARA-analytics using the TLC/FID technique. The proportions of saturates, aromatics, resins and asphaltenes were measured. The compositions of the asphaltenes were further evaluated by separation into three fractions applying a dissolution/precipitation procedure. The aging did not change the softening points of F-T wax modified bitumen, which are mainly influenced by the melting temperatures of the waxes, but resulted in the expected increase of the binder stiffness. The latter was observed through an increase of complex modulus and decrease in phase angle. This change in physical behavior caused by aging was a result of changed chemical composition: The percentage of aromatic compounds decreased whereas the fractions of resins and asphaltenes increased. Also the chemical composition of the asphaltenes changed towards the fraction of low solubility. The aging processes of the bitumen were only slightly influenced by the added F-T waxes, whilst one of the two wax types even yielded some minor advantages. These differences between the relative performances of the two wax types can be ascribed to chemical differences between them. The observed influences of the F-T waxes on the chemical composition are minor compared to the variety found for bitumen from different crude origins. The results show that the chemical composition as well as the ageing properties are predominantly affected by the bitumen characteristics, whereas effects of F-T wax do not compromise the aging properties of the binder.

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Zuletzt aktualisiert 2019-03-06 um 10:28