Best Practices for Storage and Handling Asphalt Emulsions

From storage tanks to temperature regulation, handling emulsions takes mindful calculations to achieve a desired product.

Horizontal tanks offer the advantage of being less susceptible to power lines because of their low profile, easier to recirculate and easier to drain completely.
Horizontal tanks offer the advantage of being less susceptible to power lines because of their low profile, easier to recirculate and easier to drain completely.

When customers place an order, your high caliber product will determine whether you will get repeat business and referrals. The same can be said for the asphalt industry specifically the emulsion segment. Improper storage and handling of such materials can result in unfavorable quality and performance.

According to AEMA, "emulsions come in different grades but typically contain between 55 and 75% asphalt. In addition to the asphalt and water, asphalt emulsions contain 0.1-2% of an emulsifier or ‘soap’ which functions to stabilize the emulsion."

Since the product contains about 30-40% water, emulsions behave similar to water depending on the grade. The advantage to this is safety, however the disadvantage is it will freeze at 32° F and will boil at 212° F. Keeping the material in that sweet spot, warm but not too hot, and not allowing it to freeze is key. With proper storage and handling of the materials, terminal operators will be able to create the ideal product for road ready use.

How to Choose the Right Tank?

Similar to how Goldilocks wanted to find the perfect temperature porridge to eat, making sure the temperature was just right, not too hot and not too cold, emulsion temperature is the same way. The type of tank used to store the emulsion products can and will determine the temperature of the end product.

“There are a lot of options for storing asphalt emulsions that are available to use as producers,” said Dan Swietz, director of mix design laboratories, H.G. Meigs Paving Asphalts & Emulsions. "Vertical tanks are preferred in the asphalt emulsion industry, for practical advantage."

Vertical tanks minimize surface area of the amount of area that the finished product is exposed to air and can be generally easier to mix and insulate. According to PPRA, "a skin of asphalt can form on the surface of emulsions when exposed to air." Most of the fixed tanks at terminals are vertical, but horizontal tanks are often used for short-term field storage and can offer benefits like easier to recirculate completely and easier to drain. The horizontal tanks are also primarily used for niche applications like seal coat materials.     

There are four relevant materials for construction (MOC) for emulsion terminals. The MOC is dependent on corrosivity or contained material, desired storage temperature and structural demands along with cost vs expected operating life.

"Polymer or poly-tanks are not very expensive and can cover a wide range of chemical compatibility, easy to move and even temperature to some extent," adds Swietz.

There are four relevant choice of materials of construction (MOC) for emulsion terminals.Dan Swietz

Other Storage Vessels

The terminal may occasionally make a specialty or a niche emulsion mix in a small quantity. Instead of taking up a full tank, other storage vessels may come in handy.

  • IBC (International Bulk Containers) totes: Limited use or small scale, very limited storage or select products.
  • Drums: Dry good can be stored in super sack or storage silos

In both cases, be sure to keep materials out of sunlight and shield them from the elements.

“For terminals that make a lot of different products, specifically a lot of different products on a nonroutine basis, IBC totes can be very advantageous," said Swietz. "There are some states that do not allow certain chemicals to be stored certain ways. Always default to local regulations when determining storage options for your terminal.”

Hot Topic: Temperature

When it comes to temperature inside the tank itself, it is much more cost effective to maintain rather than ramp up temperature. And each specific product needs that perfect climate to maintain its integrity because at elevated temperatures the water in the emulsion will evaporate, changing the characteristics of the product.

Tanks must also be insulated with weather resistance covering to protect the emulsion from freezing and provide the most efficient use of heat.

Several types of heaters may be used for asphalt emulsion. The main requirement is that the heater be regulated to provide the desired temperatures and that it use indirect heat instead of direct heat, such as an open flame. Additional information can be found in AEMA's, A Basic Asphalt Emulsion Manual. 

  • Steam heating: Steam can be circulated through coils delivering heat and is commonly used to unload AC rail cars.
  • Hot oil heaters:  These self-contained heaters heat a special heat transfer fluid using gas or diesel burners or electricity. The pump circulates the hot oil through the system but must be kept 185 ° F or below.
  • Water: Water can be headed by hot oil, steam or electricity. This is a safe method since water rarely gets hot enough to damage the emulsion.
  • Electrical: These heater offer the advantage of eliminating tank coils and related plumbing required for hot oil, steam or water. Some method of moving emulsion over heating surface should be considered.

"Avoid temperature swings," said Swietz. "Keeping the temperature well below boiling point is really the way to go."

Moderate Agitation Preferred

Gentle agitation or turning over is usually all that is needed. Avoid splashing or pushing air through the product with tender mixing.  

"Mixing is okay," said Swietz. "We typically mix our 40,000 gallon tanks once a day or every other day for 30 minutes and proceed to taking samples to make sure the product is okay."

The side entering propellers on the tank should be turned slowly (approximately 60 RPM) and should only be utilized when there is sufficient emulsion for proper mixing, according to PPRA's storing asphalt emulsion guide.

“You need to consider mixing because temperature segregation is a real thing especially in tall vertical tanks," said Swietz. "Mixing can help create a more homogenous mixture, which helps in the QC and QA world, where taking a sample from one valve or one part of the tank you need to make sure that one part is representative of the whole tank.”

Emulsions, like all construction products must be handled with reasonable care. The use of protective clothing (long sleeves, rubber gloves, goggles, etc.) will protect the skin from accidental contact. If there happens to be a spill while mixing, testing or transporting, contain the spill with sand or dirt and dispose of the absorbent solid in accordance with local regulations.