ABSTRACT
This chapter argues that the flexible road structure consists of a number of layers of different materials. Roads deteriorate in a number of ways, but broadly there are two forms of failure (functional and structural). Functional failure (distress) is usually associated with the road surface through deterioration with time. Structural deterioration (failure) develops gradually with the continued application of wheel loads. Fatigue cracking arises from the fact that under repeated applications of tensile stress/strain, a bituminous material will eventually fracture. A number of laboratory tests have been developed to assess the fatigue characteristics of bituminous materials. Fatigue tests may be conducted in two ways. They may be constant stress tests, where each load application is to the same stress level regardless of the amount of strain developed. Alternatively they may be constant strain tests, where each load application is to the same strain level regardless of the amount of stress required.
