Bitumen ageing and hydrated lime

Sammanfattning: This doctoral thesis consists of a literature review andfour papers describing experimental studies of the influence ofhydrated lime on bitumen ageing.The literature review describes contemporary knowledge ofbitumen with respect to chemistry, rheology and modification.The relation between chemical composition and mechanicalbehaviour is discussed. In a section on rheology, a distinctionis made between fundamental mechanical properties, related toconstitutive equations, and empirical properties related solelyto the test methods used. Mechanisms of bitumen ageing aredescribed, with focus on oxidation, which is generally acceptedas most important. Various factors affecting ageing arediscussed as well as additives for the inhibition of bitumenageing: anti-oxidants, hydrated lime and polymers.Since the beginning of the 1970s, hopes have been thathydrated lime, beside being a useful antistripping agent, alsomight work as an inhibitor of bitumen hardening. Theseexpectations appeared to be supported by the results of severallaboratory investigations. In studies presented in this thesis,laboratory ageing of bitumen was performed using standardisedmethods generally accepted to resemble real life conditionsduring production and service. The results show that under suchconditions, the anti-ageing capacity of hydrated lime is fairlymodest. However, it was also shown that using more severeageing conditions hydrated lime can produce a strikingreduction in the ageing index.There are several pathways of bitumen oxidation, includingcatalysation. Different metal-containing compounds naturallyoccurring in bitumen, in particular various vanadium complexes,are supposed to catalyse bitumen ageing. One mechanism ofhydrated lime that has been suggested is the inhibition ofcatalyst-induced oxidation. Indications in favour of thisproposition were provided by an ageing study in which variousamounts of a vanadium-containing catalyst was added tobitumen.The mechanical properties of bitumen are highly dependent onmolecular polarity. Since hydrated lime is a surface-activematerial, it is reasonable to expect that hydrated lime has asignificant impact on molecular configurations andstructure ofbitumen. Accordingly it appeared possible that hydrated limeaffects low temperature physical hardening and low temperaturemechanical properties such as the capacity of dissipation ofstored deformation energy. A study was performed using abending beam rheometer (BBR) for comparative tests of samplesthat were either neat or contained hydrated lime or a calciumcarbonate filler. However, the low temperature physicalhardening reflected no significant influence of thefillers.KEYWORDS:bitumen, asphalt, ageing, additives, hydratedlime, rheology, IR-spectrometry, dynamic mechanical analysis(DMA), bending beam rheometer (BBR), vanadium chelates,literature study, low temperature physical hardening.