Age hardening potential of tall oil pitch modified bitumen

The long-term ageing characteristics of bitumen modified using tall oil pitch (TOP) were investigated. Bitumen containing various proportions of TOP was aged as 1 mm thick films at 60 degrees C for 3024 hours. The TOP modified bitumens displayed an increased ageing index and viscoelastic modulus after ageing indicating that they are more susceptible to oxidative ageing than conventional bitumen. Determination of the Heithaus parameters of aged samples showed that an increase in the TOP content caused a reduction in the asphaltene dispersability (P-a), an increase in solvent power (P-0) of the maltene phase and an overall improvement in compatibility (P) of the bitumen. A significant increase in asphaltene content with increasing TOP content also occurred after ageing. The acid number of the bitumen increased in proportion to the TOP content, but did not change after ageing. It is postulated that unsaturated carboxylic acids in the TOP are susceptible to oxidative polymerisation, which leads to the creation of large, highly polar, asphaltene-like molecules. It is these oxidised carboxylic acids, which cause the bitumen to harden more as it ages.