Asphalt Emulsion and Manufacture (Lloyd A. Hall & Edwin E. Mortell, No. 1,883,658)
Patented on October 18, 1932, this invention describes a method for creating a highly stable, “rejuvenatable” asphalt emulsion. The key innovators include Lloyd A. Hall, a pioneer in food chemistry and industrial science, and Edwin E. Mortell.
The primary challenge they solved was the tendency of asphalt emulsions to “break” (separate) or be permanently ruined by freezing. This invention produced a smooth paste of minute asphalt particles that remains stable over long periods and can be easily restored even after being frozen.
1. The Composition: Asphalt, Clay, and Water
The emulsion is not a chemical reaction but a physical suspension of three main components:
- Asphaltic Substance: This can be natural asphalt, pitch, or petroleum residue. The inventors preferred an asphalt with a relatively low softening point (around 100 degrees F to 105 degrees F).
- Colloidal Clay (Bentonite): Bentonite acts as the “emulsifying agent.” It surrounds the tiny droplets of asphalt, preventing them from merging back into a solid mass.
- Water: The dispersing medium. In the final concentrated paste, the weights of water and asphalt are roughly equal, with clay making up about 4% of the weight.
2. The Manufacturing Process
The stability of the product depends heavily on the method of mixing, which follows a specific sequence:
- Preparation: A suspension of bentonite clay in water is heated to roughly 125 degrees F. Simultaneously, the asphalt is melted and heated to a much higher temperature, between 275 degrees F and 300 degrees F.
- Preliminary Emulsification: About 5% of the total batch is mixed first. This small “vehicle” helps the rest of the materials emulsify more evenly.
- Equivalent Addition: The remaining heated clay suspension and heated asphalt are poured into the mixer together in balanced proportions over 15 to 20 minutes. This ensures that neither component is in excess during the formation of the particles.
- Natural Agitation: The mass is stirred for 40 to 50 minutes, during which it naturally cools to about 115 degrees F.
3. The “Chilling” Step
The most critical innovation in this patent is the rapid chilling at the end of the process.
While the mixture is still being agitated, cold tap water (about 60 degrees F to 70 degrees) is added suddenly. This drops the temperature of the emulsion to roughly 70 degrees F to 80 degrees F, which is safely below the melting point of the asphalt.
Why it works: This rapid cooling “sets” the asphalt droplets while they are still tiny and separated by the clay. It prevents the particles from aggregating (clumping), which is the secret to the emulsion’s permanence and its ability to survive a freeze-thaw cycle.
4. Characteristics and Uses
Once dried, the coating exhibits several high-performance properties:
- Ductile and Elastic: It won’t crack in the cold or sag in the heat.
- Weatherproof: Resistant to air, water, acids, and alkalis.
- Versatile: Can be applied as a paint or a thick protective layer.
Common Applications in 1932:
- Air-proofing and water-proofing steel, iron, and wood.
- Coating fiber boards and cork-board insulation.
- Priming concrete roofs and floors.
Technical Summary
| Step | Temperature | Duration | Purpose |
| Heated Clay | 125 degrees F | N/A | Prepares the emulsifying agent. |
| Melted Asphalt | 300 degrees F | N/A | Liquefies the coating material. |
| Agitation | around 115 degrees F | 40-50 min | Forms the minute asphalt particles. |
| Chilling | 70 – 80 degrees F | 5-10 min | “Sets” the emulsion for maximum stability. |
Historical Significance: Lloyd A. Hall
Lloyd A. Hall was one of the most brilliant industrial chemists of the 20th century, holding over 100 patents. While he is most famous for his work in food preservation (like curing salts and antioxidants), this patent demonstrates his deep expertise in colloidal chemistry—the science of how different substances stay mixed together. His work on this asphalt emulsion helped create more durable building materials that could be stored and shipped without spoiling.
