Asphalt Emulsions and Emulsifying Agents - A little chemistry
The purpose of making water-based asphalt emulsions was originally to make the asphalt easy to handle at relatively low temperatures. In emulsion manufacture, a chemical emulsifying agent is used to stabilize the emulsion (to keep the oily asphalt particles suspended in the water--or to make "oil and water mix"). The agent normally has little effect on the properties of the asphalt after the emulsion has cured. The exception to this is a special family of emulsifiers called "high float agents". When the water leaves the emulsion, the chemical emulsifying agent is left behind in the cured asphalt emulsion residue. The high float agent molecules orient themselves to form a networked gel structure within the asphalt, giving structure and physical properties very similar to "Jello". This gel structure keeps the asphalt from flowing, much like the Jello which maintains its molded shape.
High float emulsions are formulated to give optimum emulsion stability and optimum physical properties to the cured residue. The soapy chemicals used are similar to those in the pine cleaner you use at home.
Less susceptible to temperature extremes
What does this mean to the physical properties of the cured asphalt emulsion residue? The gel structure keeps the asphalt from flowing at high temperatures, such as those at the surface of an asphalt pavement on a hot summer day. The result is an improvement in temperature susceptibility--less brittle at low temperatures, and therefore more resistant to thermal cracking. At high temperatures, the gel structure keeps it from being as runny, preventing tenderness, bleeding and asphalt run-off or draindown.
| The Float Test |
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What does "high float" mean?
It means the emulsion residue passes the "float" test (ASTM D139; AASHTO T-50). In this test, the residue from distillation is poured into a short open-ended brass collar, and allowed to cool. The collar is then screwed into the bottom of a small aluminum float. This is put into a water bath at 60°C (140°F). To pass the test, the assembly must float on the surface of the bath for a minimum of 1200 seconds (20 minutes).
Used in almost every state
ASTM, AASHTO and more than 41 States have recognized the value of the float structure, and currently have specifications for high float emulsions.
High Float emulsions are just one of the tools used by SemMaterials technologists to provide cost-effective solutions for our customers. We formulate emulsions and design systems for your needs. For more information on the grades of high float emulsions specified and available in your area, or help in choosing the right treatment for your pavement, contact your local SemMaterials representative.