The most common way in which bitumen is applied to mineral aggregate substrates in road making processes is in the form of a so-called 'bitumen emulsion'. Bitumen emulsions are a dispersion of bitumen in an aqueous continuous phase, stabilised by the addition of an emulsifier. They are usually prepared as genuine emulsions at high temperatures, but applied as solid dispersions at ambient temperatures. During road making, these emulsions (or dispersions) must break over the surface of a range of mineral aggregates in a controlled manner, and hence a thorough understanding of the physicochemical properties of such emulsions, and the aggregate substrates, is required. This paper presents a summary of global industry processes for preparing bitumen emulsions (including a review of commonly used emulsifiers), and discusses the factors that can affect the characteristics and behaviour of these emulsions with particular reference to their application to mineral aggregates.
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