Conference proceedings article
Ageing characteristics of warm mix asphalt binders modified with F-T wax - Benefits for efficient application and adequate performance

Publication Details
Mollenhauer, K.; Simnofske, D.; Butz, T.; Oelkers, C.
The Southern African Bitumen Association
Sun City, South Africa
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Book title:
Proceedings 11th Conference on Asphalt Pavements for southern Africa (CAPSA 2015)
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The use of rheology modifying additives in asphalt mixes for reducing the mix production temperature and/or in-creasing 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 com-pactibility 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 differ-ent 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 mechani-cal/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 chemi-cal 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 dissolu-tion/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 in-crease 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 com-pounds 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 pro-cesses 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 per-formances of the two wax types can be ascribed to chemical dif-ferences between them.The observed influences of the F-T waxes on the chemical composition are minor compared to the variety found for bitu-mens from different crude origins. The results show that the chemical composition as well as the aging properties are predom-inantly affected by the bitumen characteristics, whereas effects of F-T wax do not compromise the aging properties of the binder.

Last updated on 2019-25-07 at 18:19