REAL Technical Data Sheet No. 1 - Bitumen Road Emulsion
Introduction
Bitumen is a product from the distillation of crude petroleum and is produced in a wide range of grades varying from hard and brittle to soft and fluid, at normal temperatures. Many of these grades are used for road maintenance and construction, and to facilitate use it is necessary to temporarily reduce their viscosity. This reduction can be achieved by the use of solvents, or by applying heat, or by a combination of solvents and heat, or by emulsification.
Bitumen Road Emulsion Bitumen emulsions are heterogeneous, two-phase systems consisting of two immiscible liquids, bitumen and water, stabilised by an emulsifier. The bitumen is dispersed throughout the continuous aqueous phase in the form of discrete particles, typically 1.0 to 10 microns in diameter, which are held in suspension by electrostatic charges imparted to the bitumen particles by an emulsifier.
Emulsions in which the bitumen particles are positively charged are known as Cationic Emulsions and those in which the particles are negatively charged are Anionic Emulsions. It is vitally important that the two types of emulsion are never mixed as this causes coagulation.
Characteristics The main advantage of Bitumen Road Emulsions is that the relatively high viscosity of cold bitumen is retained in a form which can be used easily at comparatively low temperature, such that when the bitumen is released from the emulsion the correct grade is made available for its intended purpose.
The process whereby the bitumen is released from the emulsion is known as “breaking” and involves the formation of a continuous film of bitumen from the individual discrete particles originally present in the emulsion. The breaking of anionic bitumen emulsions involves the substantial removal of water, mainly by evaporation but also by absorption through surfaces in contact, particularly those of mineral aggregates. For cationic emulsions a significant factor which contributes towards the breaking, in addition to removal of water, is a physiochemical effect which involves adsorption of positively charged emulsifiers on to negatively charged surfaces in contact, thus assisting in the de-stabilisation of the emulsion. For this reason, cationic emulsions possess good adhesive properties with respect to adhesion of the residual bitumen to mineral aggregates and are the most popular type of emulsion used.
The rate of break of bitumen emulsions is controlled by the careful formulation of the emulsion during manufacture and can be selected to be from very rapid to very slow depending upon the particular application.
Other factors which influence the rate of break include weather conditions and mechanical forces such as rolling, trafficking and mixing operations.
Specifications In the U.K., the new European Standard BS EN 13808 is used to define the grades of bituminous emulsions. Sections 3.1 Nomenclature and 3.2 Specification of current BS 434 part 1 grades from the draft notes for guidance are given below:
