Durability of bituminous paving mixtures
Bitumens are used as a binder in roadway pavements largely because they are relatively inexpensive and generally provide good adhesion and waterproofing characteristics. They are generally rather resistant to the detrimental effects of the environment and usually remain pliant for many years. In other words, bitumens are relatively inexpensive binders that generally provide good durability (or longevity of service) in pavement mixtures. Bitumens are no panacea, however. Many factors affect the durability of bitumens and, thus, bituminous mixtures. However, assuming that a pavement layer is constructed according to specifications (which attempt to account for durability), it is generally agreed that the two primary factors affecting the durability of bituminous paving mixtures are damage due to water and embrittlement of the bitumen due to age hardening. Much effort has been afforded to the study of age hardening and water damage and much has been learned. However, the exact mechanisms of ageing and water damage in bituminous mixtures remains an enigma. This thesis attempts to provide an improved understanding of these mechanisms through a comprehensive literature review, development of performance tests to assess mixture durability and investigation of the rheological characteristics of bitumens aged and tested whilst in contact with mineral aggregate.