Emulsions 101: How to properly handle, store and sample emulsions
BY AsphaltPro Staff
Editor’s Note: For 2024, AsphaltPro Magazine allows experts in the industry to share how to expand your operations to the next phase of business. Let’s turn to some professionals who have equipment, services, software and tenure to help you expand to mix design, production, hauling and more. This month’s installment looks at the use of emulsions at the terminal, hot-mix plant and beyond to enhance your asphalt mix design and pavement structures.
Proper storing, handling and transport of asphalt emulsion are critical aspects of ensuring the quality and effectiveness of this versatile material in construction projects. From maintaining the stability of the emulsion during storage to safeguarding its integrity during transportation and handling, adherence to best practices is paramount for maximizing performance and longevity.
At World of Asphalt 2024, Bob McGennis, technical manager at HF Sinclair, Dallas, which has seven refineries and four asphalt terminals throughout the United States, presented an education session on these best practices based on 25 years of experience.
Although emulsions are commonly used in pavement maintenance and rehabilitation applications, McGennis said that’s changing. “There are a number of factors that are probably going to give emulsions a higher profile in our industry,” he said. “We are on the precipice of a surge in asphalt emulsion technology because there will be an advantage to using it when we’re concerned about EPDs, global warming and life cycle analysis.”
Emulsions offer an environmentally friendly additive because they’re made workable through the mere use of water.
McGennis recommends downloading the Transportation Research Board E-C102 and the Asphalt Institute’s MS-19 to learn more about asphalt emulsions. The Emulsion Manufacturers Association is another useful resource, he added.
What Makes an Emulsion
“When asphalt is milled into microscopic particles and dispersed in water with the aid of a chemical emulsifier, it becomes an asphalt emulsion,” McGennis said.
An asphalt emulsion usually contains 50 to 70% asphalt by weight. The rest is a combination of water and emulsifying agent (together, called the ‘soap solution’). “A run-of-the-mill asphalt emulsion concentrate is somewhere around 65% asphalt and 35% soap,” McGennis said. “Then there’s all kinds of other stuff that can be thrown in, such as polymers, adhesion promoters, rejuvenators.”
The asphalt and soap run through a colloid mill where the rotor grinds the asphalt into tiny droplets anywhere from one to 10 microns in size. “These particles are so fine, they would completely pass through a #200 sieve,” McGennis said.
What keeps the droplets separated is the emulsifying agent coating each asphalt particle. The emulsifying agent is either positively charged (cationic) or negatively charged (anionic). “We know like charges repel one another,” McGennis said. “That’s what keeps the emulsion droplets stable in the system.” On rare occasions, an emulsifier may be non-ionic, which works a bit differently. “They actually have a coating that keeps those droplets separated,” McGennis said.
McGennis said anionic agents are typically fatty acids, historically products of the wood processing industry. “Because they’re an acid, you mix them with some kind of base, typically sodium hydroxide or caustic,” he said.
Cationic emulsifiers are typically fatty amines, originally almost completely animal-derived such as tallow. “We actually mix these fatty amines with some type of acid, typically hydrochloric acid,” he said.
The goal of the emulsifier is to keep the emulsion stable enough to survive manufacturing and use, but unstable enough for the desired setting behavior. “You’ll hear people say, for example, in the case of chip sealing, that you want to get the aggregate on that film before the emulsion breaks,” McGennis said. “What’s happening [when it breaks] is the droplets [of asphalt] are coalescing as the water leaves the system. How fast that occurs indicates the [emulsion] classification.”
The volume of the emulsifier depends on the application for the product. For example, a spray application such as a chip seal would require less emulsifying agent as this instability of the emulsion reduces setting time, while a mixing application such as through a pugmill would require more emulsifying agent to remain stable through mixing, hauling and paving.
Classifications of Emulsions
Emulsions must be viscous enough to spray and cover a surface without running off the road. They must also be able to hold aggregate without raveling, nor bleeding under traffic. “There are a lot of different expectations that we have of emulsions,” McGennis said. “That’s why there are so many different grades, in order to fulfill the needs of each application.”
A few years ago, McGennis set out to count the classifications of emulsions and discovered more than 300 classifications in 25 different use categories (most in roadwork). Let’s take a closer look at various features of emulsion classification:
- Charge: The first letter (or lack thereof) in an emulsion classification denotes if the mix is cationic or anionic. If cationic, the classification will contain a C. An anionic emulsion, however, will not have an A—there will be no letter at all. There’s also high float emulsions, a special category of anionic emulsions denoted with an HF.
- Setting speed: Rapid set emulsions break quickly and are denoted with an RS. Slow set emulsions are denoted with an SS. In between slow and rapid are medium set (MS) and quick set (QS).
- Viscosity: A number 1 in the classification means the emulsion itself has a low viscosity while a 2 indicates higher viscosity. The viscosity of the base asphalt may be designated in the classification of the emulsion with a H at the end to indicate a harder base asphalt.
So, a CSS1H would be a cationic slow set with low viscosity with a harder base asphalt, while a CRS2 (the most common chip seal grade) would be a cationic rapid set with high viscosity. However, classifications don’t stop there.
For example, a CRS2P is the most common polymer modified chip seal grade, denoted with P at the end, while CRS2L denotes injection of latex. “There’s a whole raft of products out there that have been developed which use rubber, recycling agents or rejuvenating agents,” McGennis said.
There’s polymer-modified rejuvenating emulsion (PMRE) and emulsified rejuvenating agent (ERA1). There’s CIREE (cold in-place recycled engineered emulsion) and CREE (cold recycled engineered emulsion).
Despite decades of experience, McGennis said there are some classifications that still stump him. “It can be a bit of alphabet soup,” he said. “You have to look at the spec to really figure out what it is they’re wanting to use those for.”
Best Practices of Loading Emulsion
“You have to be careful when you load transports to make sure that the emulsion that you’re loading into the transport is compatible with what was previously in the transport,” McGennis said.
For example, if the trailer you’re loading cationic emulsion into was last used for hot asphalt, “you absolutely don’t want to load the emulsion because that asphalt could be hotter than the boiling point of water and you could, well, it’s like a volcano exploding.”
If it’s been hauling crude oil or heavy fuel oils, McGennis suggests emptying to no measurable quantity. “If you look down into the trailer with a flashlight, you might see a thin ribbon of oil down at the bottom, and that would probably be okay, but you’d prefer to have it as empty as possible.”
“If they’ve just been hauling another load of cationic emulsion, then you’re good to load,” McGennis said. If the trailer’s been hauling an anionic emulsion, it must be emptied to no measurable quantity or preferably flushed out.
“If you load cationic and anionic together, instead of those particles pushing each other apart, they come together and you could end up with basically clabbered milk,” McGennis said. Many suppliers will either avoid handling both anionic and cationic emulsions or use separate, dedicated trailers for each type. “If you’re going to use a distributor to spray tack and to do a chip seal, if you’re using cationic to chipseal, use cationic to tack.”
If you don’t know what’s been in that trailer, McGennis said the trailer should be thoroughly cleaned.
Best Practices for Storing Emulsions
McGennis recommends storing emulsions in vertical tanks versus horizontal tanks. “If you go to an emulsion supplier, that’s what you’ll see because it exposes the least amount of surface area,” he said. “If you go look at the top of the emulsion in that tank, you might see it a bit broken on top, and that’s okay. That actually protects what’s underneath.” Just don’t pull that material for samples, he said.
In many maintenance yards, McGennis sees horizontal tanks. “It’s okay, because typically the emulsions they’re using in those types of applications are tack oil and other more forgiving applications,” he said. “But, the vertical tanks are best practice.”
Of course, tanks should be insulated and have sample valves. McGennis said it’s best practice to avoid agitators. “You don’t want vigorous agitation,” he said, opting instead for “a rod going uniaxially down the tank, with a couple of propellers gently circulating [the emulsion].”
Best Practices of Sampling Emulsion
In order to achieve accurate samples, McGennis recommends applying the following best practices.
“When you take the sample, allow about a gallon to run out so that you’re not testing the stuff that’s been left in the sample valve from the previous time that somebody took a sample,” he said.
Samples should not be collected in metal cans, as the extreme pH levels of emulsion (anionic is usually 10 to 12, and cationic is usually 1.5 to 2.5) can react with the metal. “It can actually break the emulsion or it’ll make it seem like the emulsion is out of spec when it’s really not,” McGennis said, suggesting the use of plastic cans.
Once the material is in the container, allow the emulsion to cool before putting on the lid. “As the emulsion cools, it shrinks and sucks in the can, and you run the risk the emulsion will escape,” McGennis said.
HF Sinclair uses triple containment for its samples: a plastic container, in a plastic bag, in a box. “There’s even an absorbent in there in case the box gets squished,” he said.
Although taking samples in the field makes sense because that’s where the emulsion is being used, McGennis warns that these emulsions are designed to be unstable for optimal setting. “All the specification requirements are written around tank samples,” he said. “In other words, undisturbed samples.”
McGennis strongly cautions against taking samples from the spray bar. “By then, the emulsion has been run through at least one pump, if not two,” he said. “It might be contaminated with [cleaning product] that they back flushed their pump with from the day before, and that would make the base asphalt look too soft.”
The second issue with sampling from the spray bar, especially if the emulsion has been in the spray bar for a while, is that it can come out already broken. “It could be like clabbered milk,” McGennis said. “It would not pass the sieve test.”
“That’s why distributors as they come from the manufacturer all have a sample valve where you can get a tank sample that is more representative for determining specification compliance,” McGennis said.
Once the samples are taken, proper handling is also important. “Everyone’s heard the urban legend of the DOT inspector grabbing the sample and throwing it in the back of a pickup truck for a week before taking it to the lab to be tested,” McGennis said. “The last thing you want to do is not take care of that sample. These emulsions are designed to be somewhat unstable. You want to handle them with care.”
