Design and construction of asphalt bases and surfacings

The term ‘asphalt’ is generally taken to refer to a bituminous material comprising a mixture of aggregate bound with bitumen that is almost exclusively used in road construction. In addition to the graded aggregate and bitumen, the mixture also contains a small proportion of air. Thus, bituminous materials are three-phase materials, and their properties depend upon the properties of the individual phases as well as the mixture proportions. The two solid phases are quite different in nature – the aggregate is stiff and hard while the bitumen is flexible and soft and is susceptible to temperature change. Therefore, the proportion of bitumen in the asphalt mixture has a great influence on the mixture properties and is crucial in determining the performance of the material.