A brief history of the development of bitumen emulsions
In 1906, the first patent covering the application of dispersions of bitumen in water for road building was taken out (Van Westrum, 1906). Initially, efforts were made to form emulsions by purely mechanical means. However, it rapidly became apparent that mechanical action alone was insufficient, and, since these pioneering days, emulsifiers have been used in the process (Albert and Berend, 1916). At first, the naturally occurring organic acids in the bitumen were utilised by adding sodium hydroxide or potassium hydroxide to the aqueous phase. The subsequent reaction formed an anionic soap that stabilised the dispersion (Bradshaw, 1960). A great variety of acidic chemicals has been used to promote the stability of anionic bitumen emulsions. These include residues from fatty acid distillation, rosin acids, hydroxystearic acid and lignin sulfonates, all of which may be blended with the bitumen prior to emulsification or dissolved in the alkaline aqueous phase. Since the early 1950s, cationic emulsifiers have become increasingly popular because of their affinity for many solid surfaces. This is an important property in road construction because the good adhesion of bitumen to different types of mineral aggregate is essential. The most widely used cationic emulsifiers are amines, amidoamines and imidazolines (Schwitzer, 1972). In the mid-1980s, following the development of polymer modified binders, modified bitumen emulsions based on different manufacturing processes were produced. The residues of these bitumen emulsions had superior properties compared with traditional emulsions, and exhibited improved performance in specific applications (discussed further in section 9.6).