Prime coats and granular sealing refer to sprayed treatments intended to bind and stabilize the granular material on roads and on unpaved roadway shoulders. In addition to conferring cohesion and bond, these treatments also protect the underlying layers of granular material from moisture by creating a waterproofing layer at the surface. This paper presents the development stages of a solvent-free asphalt emulsion designed to match the performance of a cutback primer. Starting with the basic principles such an emulsion has to meet, a number of formulations have been produced, tested and optimized at the laboratory level. Specialized tests such as the Modified Sand Penetration Test were used to assess duration and depth of penetration of the emulsions into granular materials having different mineralogy, different levels of compaction and variable moisture content. A number of field trials of granular sealing on shoulders were done during 2006 and 2007, using emulsions optimized as described. Penetration during spraying was very good and performance to date of the treated areas is excellent.
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