èxtënsion within the half decade in the United States of the use of asphalt in emulsified or dispersed form in the road-building field has brought about problems of formulating specifications for such material by highway and road-building engineers.
The use. of emulsified asphalt as a binder in the lowcQst road field has met with favourable reception. Special attention to low-cost roads has been stimulated by economic study, the desire to serve less-heavily populated areas, and by the completion of heavy-traffic road systems in many parts of the country.
The problem of manufacturing and defining suitable emulsified materials must be considered in the light of new types of road construction which have been successfully developed by engineers. Emulsified asphalt, suitable for one type of construction, may not be at all suited for another. It is to be expected that bituminous materials in. dispersed form must be satisfactorily adapted for the intended use, much as with other bituminous binders, although from an engineering and technical point of view, the adaptability of emulsified asphalt entails problems peculiar to this type of material.
Construction types in which emulsified asphalt may be successfully employed, will vary widely from conventional and generally used penetration types, surface treatments and mixed-in-place work, to the types of mechanically prepared plant mixtures with open and with standard graded aggregates. It is obvious that one type of emulsion will not serve all purposes.
While the more important manufacturers of emulsified asphalt have been successful in co-operating with engineers in producing the highest types of materials suitable for their special needs, the methods of defining, testing and specifying the various grades of materials required, are open to much confusion. The lack of uniformity in various state specifications for the same type of use, results in great hardship to the manufacturer, as well as in increased cost which must be passed on to the consumer. The significance of many of the specification tests is not yet fully developed, nor satisfactorily related to field practice. This is a natural consequence of the more rapidly developing uses, as compared with the more tedious development of testing technique.
It is the writer's purpose to discuss the properties required for road-building emulsions and the significance of testing methods commonly employed in the United States to describe them.
Further,__ where possible, values are suggested for requirements for good quality and performance consistent with modern manufacturing and construction specifications.
Without attempting to differentiate between grades of emulsified asphalt, it is evident that for satisfactory use, the requisite properties for successful road application must fall within the following general
