ABSTRACT
This chapter describes the development of asphalt paving in the 20th century – a process driven by the advent of large fleets of self-powered trucks and the availability of powerful machinery for manufacturing and placing asphalt. Furthermore, in the 19th century the proportions of the components of natural rock asphalt rarely led to an asphalt suitable for paving. Manufactured asphalts using bitumen as the mortar in a sand mix were only used for surfacing. On the other hand, the availability of bitumen-rich material from Trinidad showed that bitumen could be used as a paving material in its own right. By 1907, the use of bitumen from oil refining had exceeded the usage of Trinidad Lake bitumen. The first modern asphalt plant was built in 1901 by Warren Brothers. Improved machinery after the World War I led to even better asphalt mixes. The effective mechanical spreading of pre-mixed asphalt did not occur until the 1930s. The product produced by the new equipment was called hot mix asphalt. As experience with asphalt continued, there was a growing realisation that asphalt could be used not only as a surface course but also as a structural basecourse. By the 1930s, the spreading and rolling of pre-mixed asphalt in multiple layers was possible. The incorporation of broken stone into mastic mixes to produce a strong manufactured asphalt was a gradual process. The grading of the stone and sand and the amount and viscosity of the bitumen used were carefully selected.
