Improvement of Asphalt by Addition of Rubber and Latex

Abstract

Abstract Since the technical expressions and measurement methods appearing in this article are apt to be unfamiliar to many readers, they will be defined briefly. It is realized that on the one hand a certain eonfusion in concepts exists with respect to the terms bitumen, tar, and asphalt, and on the other, the test methods leave much to be desired, in the opinion of experts in the field. Bitumen differs from tar in its origin, for one thing. Whereas tar is the residue of the distillation of coal, bitumen is understood to be distillation residues derived from petroleum. Bitumens are colloidal systems, one phase of which contains organic substances, dispersed in the second phase, which consists of hydrocarbons having different molecular weights. Asphalt is understood nowadays to be a mixture of bitumen and mineral substances. Such mixtures, when found already combined in nature, are called natural asphalt, asphaltic rock, or crude asphalt. The uses of bitumen in technology and industry are very manifold; mention need be made only of applications for roofing paper and electrical insulations, in construction both below and above ground, for interior, exterior, and underwater coatings, for sealing purposes, and in the rubber industry. Of special importance is the use of bitumen in road construction. The combined use of bitumen and rubber is very old. Pertinent patent applications go back to the year 1843. Large scale experiments with rubber-modified bitumen in the road construction sector have been going on for about 30 years. Important investigations and contributions have been made by Anglo-American and, especially, Dutch scientists. In the addition of rubber to bitumen, the latter undergoes many essential and (for the road engineer) advantageous changes in its properties. Before these properties are taken up individually, a report will be given of the methods of physical investigation employed to test the characteristics of both “pure” bitumen and rubber-modified bitumen. Among the tests intended to characterize the properties of bitumen are those for penetration, softening point, breaking point, flow length, ductility, tenacity, toughness, and elasticity. It was only a few years ago that another method was developed, which provides for a very practical assessment (and one suitable for industrial applications) of the essential characteristics of rubber-modified bitumen. These basic features are useful for putting into proper perspective the unusual improvements which can be realized by the addition of rubber. This new method is known in the literature as the “tenaacity—toughness test. It will be explained later on, in more detail. The various methods can be summarized as follows: