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. Are you ready to take the plunge and increase your recycling efforts? 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 from Sripath Technologies takes a look at methods of increased recycle content with mini case studies of the company’s additive products.

A primer on how high-RAP mixes are made and used

When an asphalt pavement reaches the end of its life, it is milled off the roadway and crushed to create reclaimed asphalt pavement (RAP). Over time, mountains of RAP can accumulate—depending on the depth milled, just one lane-mile of pavement can generate several hundred tons.

For decades, RAP was considered a burden—waste material to be used on shoulders or stored in ever-growing piles. It was not until the 1970s that our industry began to realize its incredible potential for reuse and recycling. The National Asphalt Pavement Association (NAPA) reported in 2021, over 95% of RAP generated in the United States is reincorporated into new pavement. And it’s not hard to see why. The use of RAP presents a trifecta victory for business through cost-savings, sustainability and road performance.

Contractors champion recycling as it helps them save on raw materials like virgin asphalt binder, typically the greatest expense in mix production. Reuse also benefits the environment, as it keeps old pavement out of landfills and reduces demand for carbon-intensive virgin materials, thereby cutting greenhouse emissions. And many transportation agencies now recognize that high-RAP roadways made with proper ingredients and mix design can yield equivalent performance to virgin-material pavement. Given its growing popularity, understanding the fundamental steps involved in RAP recycling is important for anyone in the asphalt industry.

Best Practices for Mobile Asphalt Crushing

Sourcing and Preparing RAP

The first step is to source and prepare your RAP, which can come from anywhere there was once asphalt pavement, including waste material from production facilities. Many transportation authorities are indifferent to RAP sourcing, as long as final aggregate and mix characteristics meet their specifications. However, some agencies are more restrictive, allowing only RAP that can be traced back to a specific project.

RAP particle size varies significantly, ranging from fine to coarse particles. Variability must be addressed, as an improper ratio of small to large particles can lead to poor gradation. Too many large pieces will not pack together properly, leaving excessive space between particles. Too many small particles will make the mix overly dense and therefore susceptible to cracking. Thus, it is important to classify RAP into different size fractions, allowing contractors to produce high-performance mixes that incorporate RAP from many sources.

The key stages of RAP preparation are:

• Screening: Mechanically screen RAP to separate large pieces and remove extraneous materials
• Crushing: Break apart large pieces with a crushing machine. Avoid pulverizing particles that are already small, as it will create dust.
• Fractionation: Separate and sort the crushed RAP into multiple size groups. Although this practice is not done in all asphalt recycling operations, it allows for a more flexible mix design and the use of higher RAP content.
• Homogenization: Once sorted into piles of different sizes, turn over each pile several times to make a more homogenous feed stock for plant operations.

Step Up Hot-Mix Production with Your Facility’s Own Crushing Plant

Sampling and Mix Design

To design a high-performance mix, it’s important to properly characterize the RAP aggregate and binder. Start by sampling the crushed and homogenized RAP stock, making sure to retrieve several representative samples. Extract aggregates from the RAP sample using an ignition oven or solvent. Determine the size analysis of these aggregates. It is important to have an optimal balance of fine and coarse particles. Next, extract and determine characteristics of the aged binder, as its properties will affect the final mix.

Crucial for the success of high-RAP mixes is a carefully engineered and balanced mix design. Fortunately, designing a high-RAP mix is similar in many ways to designing a traditional mix, aside from a few key steps. First, you must account for binder content in the RAP when determining how much virgin bitumen to add. Without factoring this into your calculations, the mix will likely be too rich in binder content. Second, most mixes with more than 25% RAP content, will require an asphalt rejuvenator or recycling agent. Many recycling agents are available, and choosing the right one will make a substantial impact on the pavement’s performance and lifespan. It will also affect your manufacturing and paving efficiency.

An ideal rejuvenator should:

• Soften the aged RAP binder,
• Restore the functional properties of the aged binder,
• Deliver excellent roadway performance and durability,
• Help improve compactability of stiff RAP mixes.

Designing a high-RAP mix requires a careful balance between cracking and rutting resistance. Several methods exist to evaluate cracking, including the Disc-shaped Compact Tension (DCT) test, Semi-Circular Bend Test (SCB), IDEAL-CT, Texas Overlay, and I-FIT test. Some commonly used methods to evaluate rutting performance include: Hamburg Wheel Tracking (HWT) and Asphalt Pavement Analyzer (APA) rutting test. Contractors nationwide have used Balanced Mix Design protocols to reap the benefits of recycling while maintaining excellent road performance.

VDOT Demo Rejuvenates High-RAP

RAP In Action

One recent case study comes from the Virginia Transportation Research Council (VTRC), which organized a high-RAP demonstration trial in Ashburn, Virginia. Around 6,000 kg of PG64-22 binder dosed with ReLIXER®, an asphalt rejuvenator manufactured and marketed by Sripath®, was mixed with 40% RAP and fresh aggregates to produce about 2,000 metric tons of high-RAP mix. This mix was used to pave a 40 mm wearing course on an approximately 8 lane-km stretch of roadway in Ashburn, Virginia. As shown below, binder extracted from the high-RAP mix showed characteristics comparable to binder from the low-RAP control.

Another success story comes from the Illinois State Toll Highway Authority, which manages a 475 km network of highways across Illinois, subject to high traffic and extreme weather conditions. Close to 5,000 tons of a 40% ABR mix was produced to lay down 8 lane-km of wear, base, and shoulder courses on US Interstates I-88 and I-294. ReLIXER® additions at 2.0% and 3.6% of total bitumen content were evaluated. For comparison, a “softer” bitumen mix was also evaluated. As shown in the table, the properly designed and rejuvenated high-RAP mixes surpassed all local specifications for low temperature cracking, rutting and air voids.

Recycled asphalt has made a long journey from being a waste material to becoming a cornerstone of our national sustainable infrastructure, demonstrating our industry’s dedication to environmental sustainability. The journey has only just begun. With an increase in recycling and reuse of reclaimed asphalt, the industry is poised to take advantage of the trifecta that RAP offers; a positive impact on sustainability, improved roadway performance and durability, and the benefits of cost-savings.

Matt Johnson is the president and CEO of Russell Standard, a company that provides asphalt materials, road preservation treatments and industrial asphalt solutions for the Mid-Atlantic region. Since taking the helm in 2004, he’s made it his mission to strengthen the company’s well-earned reputation for quality, partnership and innovation. His work these days focuses on getting the company back to its roots with innovation in the asphalt and paving materials departments, gearing these materials toward preventive maintenance.

“Many contractors in [Delaware] were driving to Maryland, Pennsylvania or New Jersey to pick up material. [Russell Standard’s lease of operations] will dramatically cut down on transportation costs by having a location in the state they can get the same material from. And the DOT was already having materials delivered from there. So, it’s really the local contractors that will benefit.”—Matt Johnson

See, Johnson is no outsider. He’s spent most of his life around or working in the business. Now, as CEO, he’s using his talents to refocus the company. This is a story about family, business, and the desire to establish one’s legacy after three generations of success in the paving industry.

Matt Johnson is the fourth generation of the family to lead Russell Standard. Back when he was just five years old, he was riding along with his father, Jim, to attend to business. As a teen, he helped maintain the grounds around the plants and worked on the paving crews into college. “Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

Lessons in Life, and Business 

Founded in 1929, Russell Standard has remained a family-owned business dedicated to quality and advancing the asphalt materials space. Building on the company’s nearly 100-year legacy, Johnson represents the 4th generation of his family to lead the business.

His great-grandfather, Niles Russell, established the Tri-State Culvert Company in Pittsburgh just before the Great Depression. The company sold drainage products, trucks and construction equipment. Later, Russell would expand into coal trucking, a retail coal business and a successful topsoil supply operation.

During World War II years, Russell Standard became a major supplier of liquid asphalt for the road construction industry. Over the years, the company would expand its footprint with hot-mix asphalt (HMA) plants throughout Pennsylvania. Russell also directed the expansion into the company’s first emulsion plant in Mercer, Pennsylvania, in the early 1970s.

This is when Russell’s son, Ed Russell, continued a steady focus on paving and materials.

Next, Matt Johnson’s father, Jim Johnson, expanded the paving operations while adding a second emulsion plant in Chambersburg and a facility in Akron, Ohio. He also put his stamp on things by repositioning the firm as the go-to contractor for paving.

Matt Johnson has been in the business since he began riding along with his dad when he was five years old. As a teen, he helped maintain the grounds around the plants. Late in high school and into college, he worked on the paving crews. Russell Standard is in his blood.

The aerial view of the Seaford facility in Delaware showcases best practices for piping jacketing (among other best practices) for environmental sustainability.

“Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

His experience has helped him to never lose sight of where he’s come from. The hours in the truck and office working with his father have made a strong impact on who he is now.

“I learned a lot about family philosophies, the history of why things were done, and why we still do things,” he said. He spoke with pride of how the family business has built a reputation for treating its people well and being fair with customers. “We’ve always done both of those for generations. The people part of the business has always been important because, without those people, we really don’t have a business.”

Lehman-Roberts Company Paves our Future

In addition to the big-picture learning, there was plenty to learn about managing the day-to-day.

“It really gave me a good understanding of how we do things,” Johnson said. “What’s important on jobs, being well organized, and having everything you need on hand when you need it so crews aren’t waiting. The equipment is there when they need it. So we’re efficient moving from job to job. And what we do is so seasonal, you have to be ready to go to minimize any disruption.”

But one lesson stands out the most:

“It’s a difficult, demanding job,” he said. “That’s one thing I think about all the time. I think that was a huge benefit of growing up in the field was getting an appreciation for how hard the job is.”

Matt Johnson is the fourth generation of the family to lead Russell Standard. Back when he was just five years old, he was riding along with his father, Jim, to attend to business. As a teen, he helped maintain the grounds around the plants and worked on the paving crews into college. “Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

A Renewed Emphasis on Materials

Since taking over the top post in 2004, Johnson added plants in Greensboro and Black Mountain, North Carolina; Baltimore, Maryland; and Reading, Pennsylvania. Today, his work is focused on getting the company back to its roots as a leading innovator of asphalt and paving materials geared toward preventive maintenance.

“I really like businesses where you bring in raw materials and turn them into something else,” Johnson said. “We’ve always had a manufacturing focus—we made materials and placed them. And that’s where I focus the business now—we’re mostly a materials business although we still do some contracting on projects that call for our own products.”

Safety Culture in the Workplace: How Generational Differences Present Challenges, Opportunities

The company’s commitment to innovation is evident in its founding of The Lab in 2017 to support both the material science and contracting sides of the business. Then in early 2020, Russell Standard made a significant investment in a new, state-of-the-art facility. It’s a nationally certified, AASHTO-accredited laboratory and is equipped and accredited for testing involving performance graded (PG) asphalt binders, asphalt emulsions and asphalt cutbacks. This is where the company focuses on research and development and custom blended solutions for customers.

“Our world-class lab is constantly working to ensure our material is meeting or beating specifications and operates with a near-obsessive drive to solve our customers’ biggest problems and innovate new solutions along the way.”

Johnson continued: “The Lab is a strength of ours. We’re always trying to innovate new or enhance existing products that focus on pavement preservation. And we’re extremely excited about two we’re getting ready to roll out to the market.”

• The first is a high-performance solution focused on the top-down preservation of longitudinal joints.
• Soon after, the company will be introducing an improved micro surfacing product to resist cracking.

Each is designed to give state and local agencies cost-effective and sustainably focused options for extending the life of their road networks. And will reinforce Russell Standard’s unique ability to manufacture material, lay material and test its performance to inform future innovations.

Matt Johnson said Russell Standard team members are always trying to innovate new or enhance existing products that focus on pavement preservation. “And we’re extremely excited about two we’re getting ready to roll out to the market.” The first is a high-performance solution focused on the top-down preservation of long joints; the second is a micro surfacing product focused on resisting cracking.

Expanding Opportunity

While managing production and innovation, Johnson also keeps an eye out for opportunities to expand. He recently found one in Delaware.

ICP Group’s facility in Seaford was the only asphalt and emulsion terminal in the state. After hearing the facility was for sale, Johnson and his team jumped in to negotiate its purchase. After lengthy discussions, ICP ultimately sold it back to its previous owner.

Recognizing its value to the region, Johnson’s team stayed on the offensive. In April, the company finalized a lease to take over operations at the facility from the previous owner. This move will bring Russell Standard’s proven dedication and laser-focused commitment to the Delaware Department of Transportation, counties and contractors throughout the state.

“It was a good growth opportunity to add an entire state that we had been servicing from our plant in Baltimore,” Johnson said. “This really allowed us to open up the entire state instead of just the fringes.”

Delaware now becomes the fifth state served by Russell Standard.

Matt Johnson is the fourth generation of the family to lead Russell Standard. Back when he was just five years old, he was riding along with his father, Jim, to attend to business. As a teen, he helped maintain the grounds around the plants and worked on the paving crews into college. “Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

“We’re focused on growing the materials business where we can,” Johnson said. “So anything adjacent to us is attractive. Since Delaware is an adjacent state, it’s an easy place to tuck into what we’re already doing. Any time we can find something like that, we’d certainly be interested in it.

Until this point, most contractors in Delaware had been sourcing material out of state. This move establishes a local option for materials and emulsions that will greatly save on transportation costs for everyone involved.

“Many contractors in that state were driving to Maryland, Pennsylvania or New Jersey to pick up material,” Johnson said. “It will dramatically cut down on transportation costs by having a location in the state they can get the same material from. And the DOT was already having materials delivered from there. So, it’s really the local contractors that will benefit.”

The aerial view of the Seaford facility in Delaware showcases best practices for piping jacketing (among other best practices) for environmental sustainability.

Smart Moves with Lasting Benefits

“Our crews know what it takes to perform successful, long-lasting treatments to strengthen communities and make them proud,” Johnson said. “From start to finish, our work and the way we do business all comes back to our mission—to be the most respected partner in the region by serving our team and customers like family.”

And with state and local governments focused on expenditures, Johnson knows they also keep a close eye on sustainability. By adding the plant in Seaford to the mix, “This will cut down on the freight,” Johnson said. “And it will cut down on the number of trucks on the road. There’s a lot of benefit overall.”

Luck Companies Celebrates 100 Years

When you couple this locally sourced material with the material innovations from The Lab, Russell Standard is making it easier for agencies to cut expenses while making their roads last longer and meeting sustainability initiatives. And that’s good for everyone.

“Good roads are safe roads,” Johnson said. “And the better that a state or local government maintains its infrastructure, it’s better for everybody. It’s safer for the public. It helps facilitate commerce. Everything gets into a truck at some point. Whether it comes in by ship or by rail, it ends up in a truck to get delivered. So, the better the roads are, the better the economy is.”

And that’s a fitting way to leave your mark.

During World War II years, Russell Standard became a major supplier of liquid asphalt for the road construction industry. Over the years, the company would expand its footprint with hot-mix asphalt (HMA) plants throughout Pennsylvania. Russell also directed the expansion into the company’s first emulsion plant in Mercer, Pennsylvania, in the early 1970s.

This is when Russell’s son, Ed Russell, continued a steady focus on paving and materials.

Next, Matt Johnson’s father, Jim Johnson, expanded the paving operations while adding a second emulsion plant in Chambersburg and a facility in Akron, Ohio. He also put his stamp on things by repositioning the firm as the go-to contractor for paving.

Matt Johnson has been in the business since he began riding along with his dad when he was five years old. As a teen, he helped maintain the grounds around the plants. Late in high school and into college, he worked on the paving crews. Russell Standard is in his blood.

The aerial view of the Seaford facility in Delaware showcases best practices for piping jacketing (among other best practices) for environmental sustainability.

“Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

His experience has helped him to never lose sight of where he’s come from. The hours in the truck and office working with his father have made a strong impact on who he is now.

“I learned a lot about family philosophies, the history of why things were done, and why we still do things,” he said. He spoke with pride of how the family business has built a reputation for treating its people well and being fair with customers. “We’ve always done both of those for generations. The people part of the business has always been important because, without those people, we really don’t have a business.”

Lehman-Roberts Company Paves our Future

In addition to the big-picture learning, there was plenty to learn about managing the day-to-day.

“It really gave me a good understanding of how we do things,” Johnson said. “What’s important on jobs, being well organized, and having everything you need on hand when you need it so crews aren’t waiting. The equipment is there when they need it. So we’re efficient moving from job to job. And what we do is so seasonal, you have to be ready to go to minimize any disruption.”

But one lesson stands out the most:

“It’s a difficult, demanding job,” he said. “That’s one thing I think about all the time. I think that was a huge benefit of growing up in the field was getting an appreciation for how hard the job is.”

Matt Johnson is the fourth generation of the family to lead Russell Standard. Back when he was just five years old, he was riding along with his father, Jim, to attend to business. As a teen, he helped maintain the grounds around the plants and worked on the paving crews into college. “Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

A Renewed Emphasis on Materials

Since taking over the top post in 2004, Johnson added plants in Greensboro and Black Mountain, North Carolina; Baltimore, Maryland; and Reading, Pennsylvania. Today, his work is focused on getting the company back to its roots as a leading innovator of asphalt and paving materials geared toward preventive maintenance.

“I really like businesses where you bring in raw materials and turn them into something else,” Johnson said. “We’ve always had a manufacturing focus—we made materials and placed them. And that’s where I focus the business now—we’re mostly a materials business although we still do some contracting on projects that call for our own products.”

Safety Culture in the Workplace: How Generational Differences Present Challenges, Opportunities

The company’s commitment to innovation is evident in its founding of The Lab in 2017 to support both the material science and contracting sides of the business. Then in early 2020, Russell Standard made a significant investment in a new, state-of-the-art facility. It’s a nationally certified, AASHTO-accredited laboratory and is equipped and accredited for testing involving performance graded (PG) asphalt binders, asphalt emulsions and asphalt cutbacks. This is where the company focuses on research and development and custom blended solutions for customers.

“Our world-class lab is constantly working to ensure our material is meeting or beating specifications and operates with a near-obsessive drive to solve our customers’ biggest problems and innovate new solutions along the way.”

Johnson continued: “The Lab is a strength of ours. We’re always trying to innovate new or enhance existing products that focus on pavement preservation. And we’re extremely excited about two we’re getting ready to roll out to the market.”

• The first is a high-performance solution focused on the top-down preservation of longitudinal joints.
• Soon after, the company will be introducing an improved micro surfacing product to resist cracking.

Each is designed to give state and local agencies cost-effective and sustainably focused options for extending the life of their road networks. And will reinforce Russell Standard’s unique ability to manufacture material, lay material and test its performance to inform future innovations.

Matt Johnson said Russell Standard team members are always trying to innovate new or enhance existing products that focus on pavement preservation. “And we’re extremely excited about two we’re getting ready to roll out to the market.” The first is a high-performance solution focused on the top-down preservation of long joints; the second is a micro surfacing product focused on resisting cracking.

Expanding Opportunity

While managing production and innovation, Johnson also keeps an eye out for opportunities to expand. He recently found one in Delaware.

ICP Group’s facility in Seaford was the only asphalt and emulsion terminal in the state. After hearing the facility was for sale, Johnson and his team jumped in to negotiate its purchase. After lengthy discussions, ICP ultimately sold it back to its previous owner.

Recognizing its value to the region, Johnson’s team stayed on the offensive. In April, the company finalized a lease to take over operations at the facility from the previous owner. This move will bring Russell Standard’s proven dedication and laser-focused commitment to the Delaware Department of Transportation, counties and contractors throughout the state.

“It was a good growth opportunity to add an entire state that we had been servicing from our plant in Baltimore,” Johnson said. “This really allowed us to open up the entire state instead of just the fringes.”

Delaware now becomes the fifth state served by Russell Standard.

Matt Johnson is the fourth generation of the family to lead Russell Standard. Back when he was just five years old, he was riding along with his father, Jim, to attend to business. As a teen, he helped maintain the grounds around the plants and worked on the paving crews into college. “Growing up as a kid, it was always cool to be around the equipment and that continued until I was in college,” he said. “Once I was old enough to be in the field, I started working on the road crews. It was so cool to finally work with all the equipment, see the material go down, and know I was helping to build something lasting.”

“We’re focused on growing the materials business where we can,” Johnson said. “So anything adjacent to us is attractive. Since Delaware is an adjacent state, it’s an easy place to tuck into what we’re already doing. Any time we can find something like that, we’d certainly be interested in it.

Until this point, most contractors in Delaware had been sourcing material out of state. This move establishes a local option for materials and emulsions that will greatly save on transportation costs for everyone involved.

“Many contractors in that state were driving to Maryland, Pennsylvania or New Jersey to pick up material,” Johnson said. “It will dramatically cut down on transportation costs by having a location in the state they can get the same material from. And the DOT was already having materials delivered from there. So, it’s really the local contractors that will benefit.”

The aerial view of the Seaford facility in Delaware showcases best practices for piping jacketing (among other best practices) for environmental sustainability.

Smart Moves with Lasting Benefits

“Our crews know what it takes to perform successful, long-lasting treatments to strengthen communities and make them proud,” Johnson said. “From start to finish, our work and the way we do business all comes back to our mission—to be the most respected partner in the region by serving our team and customers like family.”

And with state and local governments focused on expenditures, Johnson knows they also keep a close eye on sustainability. By adding the plant in Seaford to the mix, “This will cut down on the freight,” Johnson said. “And it will cut down on the number of trucks on the road. There’s a lot of benefit overall.”

Luck Companies Celebrates 100 Years

When you couple this locally sourced material with the material innovations from The Lab, Russell Standard is making it easier for agencies to cut expenses while making their roads last longer and meeting sustainability initiatives. And that’s good for everyone.

“Good roads are safe roads,” Johnson said. “And the better that a state or local government maintains its infrastructure, it’s better for everybody. It’s safer for the public. It helps facilitate commerce. Everything gets into a truck at some point. Whether it comes in by ship or by rail, it ends up in a truck to get delivered. So, the better the roads are, the better the economy is.”

And that’s a fitting way to leave your mark.

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.

Asphalt Emulsions Go Deep for Full-Depth Asphalt Recycling

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.

MINDS Plant Software Integrates Emulsion Control for Blythe

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.”

Why You Need to Tack Before Paving

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.

Why You Need to Tack Before Paving

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.”

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. Are you ready to start making your own hot-mix asphalt? 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 best practices you can employ with the storage silo to offer customers quick, quality asphalt mix for their paving projects.

If you’re in the hot-mix asphalt (HMA) industry, you know one of the game-changing inventions of last century was the storage silo. During his “Asphalt Plant Efficiency” presentation during a World of Asphalt People, Plants and Paving session in Nashville in March 2024, Greg Renegar, the vice president of customer success for Astec Industries, Chattanooga, discussed the benefits of planning ahead with your storage silos in mind.

If your “why” is to provide mix for both customer and in-house crews, you’ll want to plan ahead for overnight storage of appropriate mixes as you build your new plant. During his presentation to the World of Asphalt audience in March, Astec’s Greg Renegar reminded attendees the plant that can start loading out customers first thing in the morning will be the plant everyone flocks to.

As he explained, even if you have older components you’ve been unable to update the past few years, you can operate efficiently if you maintain those parts, tighten up your environmental footprint, and follow best practices, such as optimizing the use of storage silos.

Notice that’s “optimizing” the use of storage silos. Not every mix design is ideal for the suggestions to come, and we’ll talk about those.

“If you are using very low absorption aggregates, it may lead to a high film thickness and the mix is more prone to drain down.”—Steve Jackson

Solve Asphalt Plant Odor Issues

Store It for Fast Startup

Renegar’s presentation included a side-by-side comparison of operations you might be able to share with your production team to showcase what’s optimal and what’s not.

Amazing Producer ABC

Using old technology

• Starts loading out of prefilled silos at 6 a.m.
• Starts up the plant at 8:30 a.m.
• Runs two to three mixes on various jobs, with enough trucks for the day
• Runs all day with changeovers but no mid-streams
• Fills the silos at the end of the day for tomorrow’s early customers

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Struggling Producer XYZ

Using new technology

• Starts making mix at 6 a.m.
• Runs two to three mixes on various jobs, short of trucks
• Mid-streams at 8:30 for 45 minutes
• Runs another 300 tons and finishes for the day!
• Cleans out
• Gets a call at 10:15 a.m. for a 150-ton parking lot job
• Fires back up at 11 a.m., runs 147 tons, then mid-streams while paving foreman figures the last bit needed

One of the two producers in our examples is using new technology for its efficiency and sustainability but isn’t using best planning strategies. Renegar shared plants that start and stop more than three times per shift use up to 20-35% more fuel than they do when they run steadily. These percentages are published in the National Asphalt Pavement Association (NAPA) publication QIP-132.

You can probably monitor the effect of starting and stopping on your own fuel use. By using the storage silo to take up the slack and prevent starts and stops, you keep a steady, even production. Renegar stated Astec’s most successful customers are the ones who use long-term storage capabilities to become more profitable.

Think about it.

Because 95% of breakdowns occur at startup, you have a leg up on the day even if unplanned downtime hits you at first light. You also have a leg up on your competition on the other side of the county if your plant already has mix in the silo while Producer XYZ is still getting fired up.

Renegar explained it this way: “Storage in multiple silos plus planning allows FOB customers to get in and out quickly in the morning. Serving the FOB customers better than your competition will result in more business.”

Expand Into Production: Navigate the Permit Process

Design Your Storage

This isn’t rocket science. But it does require forethought. Renegar cautioned producers on some reasons you might not want to store mix overnight. For example, lack of planning from your customers could result in wasted mix. There’s no point in producing a hundred tons of state mix at 300 degrees if your top five customers will show up wanting a less-pricy mix produced at 340 degrees.

If you don’t have proper heating systems in place, you run the risk of losing mix temperature. There are companies making electric heating elements that can be placed in silo cone packages to take the fear out of overnight storage. These entities might not make the silo itself, but are experts in the manufacture of electric heating components and provide these to OEMs like CWMF Corp., Waite Park, Minnesota, who then assemble the complete silo.

Even with the concern of temperature under control, you want to consider the mix design you’ll store. Renegar listed the “fear of storing polymer” as one of the reasons producers shy away from filling up the silo overnight or over a weekend. Folks in the field echo his concern when it comes to open-graded mixes due to a phenomenon known as drain down. This is when gravity pulls the liquid asphalt cement (AC) away from the aggregate and down toward the silo cone.

Steve Jackson, the vice president of plant operations and sustainability for NB West Contracting, Pacific, Missouri, spoke of this phenomenon in stone matrix asphalt (SMA) mixes. “The worst mix that I have seen for drain down is SMA,” Jackson shared. “That is why some agencies are reluctant to remove the cellulose fibers even when you add ground tire rubber or reduce the mix temperature.”

He gave an example. “I remember an SMA project where we filled a silo, and that was all the mix that we made for the night. The first sample, from the bottom of the silo, had high AC and 1.5% air voids. The second sample, toward the top of the silo, had low AC and 7% air voids. We made the mix extra hot because it was going to spend a long time in the silo.” The expensive lesson he shared was having to mill out that tonnage and replace it.

How to Become Your Own Hot-Mix Supplier

“SMA, open-graded friction course and other gap-graded mixes are the worst for this phenomenon,” Jackson continued. “They also usually have specified minimum asphalt contents. If you are using very low absorption aggregates, it may lead to a high film thickness and the mix is more prone to drain down. When Joe Schroer (NB West’s construction materials engineer) worked at MoDOT, he evaluated some of those mixes, and started calculating the volume effective binder, and approved some of the SMA mixes with less than the minimum spec requirement AC content of 6.0%.”

In other words, there’s hope for “fixing” the gap-graded mix so it can be stored overnight for quick loadout in the morning, if you’re willing to work with it.

Malcolm Swanson, industry consultant and president of e5Engineers LLC, Chickamauga, Georgia, shared his thoughts. “Coarse graded mixes, SMAs, any mix with little surface area will tend to drain down. That is a major reason for adding fiber to a mix. Fiber adds surface area without changing gradation. The added surface gives the AC a place to hang on.”

“If the state allows the contractor to design their own non-gap-graded mixes, then the mix has the absolute minimum asphalt content, so they are less likely to drain down,” Jackson said. “If there are mixes that specify a minimum asphalt content, then I would be careful. Take a look at the aggregate absorption as well. We typically use aggregates with 1% or lower water absorptions in our high type mixes, these are mixes that we try to drop the mix temperature as low as possible to prevent drain down.”

For producers looking to optimize the use of the storage silos, it’s possible to adjust the mix design and temperature to ensure you have exactly what your customers are looking for first thing in the morning. It might take a little forethought and planning, but the producer who plans ahead is the producer who can optimize all the components for a tight environmental footprint, an efficient operation and a plant that all the customers flock to.

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. Are you ready to start making your own hot-mix asphalt? 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 from Ecosorb takes a look at the permit line-item of odor control at the plant to ensure your community relations, sustainability initiatives and production efficiency are working hand-in-hand.

In the asphalt industry, maintaining neighborly relations and curtailing odor complaints before they arise is just as important as maximizing production for every company’s long-term business continuity.

Asphalt binders are complex mixtures of organic compounds produced as a byproduct of petroleum refining. With constantly changing feedstocks, staying on top of blends is critical to controlling odors. In recent years, “opportunity crudes” have become more prevalent industrywide, and it has become necessary to balance the lower cost of these crudes with extra processing and off-gas scrubbing requirements. Another factor to consider is increased equipment maintenance and premature failure because of accelerated corrosion caused by hydrogen sulfide in lower grade crudes.

Each peak in a GC chromatogram represents the presence of a compound, identified and quantified on the x- and y-axes respectively.

During heating, mixing, transfer and application of asphalt binders, odors are often produced from volatile organic compound (VOC) emissions, which can lead to concerns from neighbors and passersby smelling the off-gas. If left unaddressed, concerns can become complaints, which can ultimately pave the way to regulation and operational restrictions.

Odor abatement is a historically difficult undertaking in the asphalt industry because of the complex makeup of bindings and numerous petrol products used in each hot mix. However, plants can now enlist the help of top suppliers with the knowledge and advanced laboratory technologies needed to chemically neutralize odor-causing components. These experts address this issue by identifying the problematic compounds, and by then creating and providing additives specially formulated to neutralize odors from various asphalt mixes.

Neutralization challenges with evolving mixes

Occupying a lower tier on the crude refining food chain, asphalt blends will always vary much more than higher-tier products, such as aviation fuels. Mixes can vary significantly from one season to the next—particularly with opportunity crudes—depending on the oil sources available and how they are processed. As a result, odor neutralization formulations must also adapt to the changing constituents of each season’s asphalt mixes.

Manufacturers, therefore, cannot always rely on the same odor-mitigating additives from one season to the next, even when producing the same end product. Additionally, since crude sources and refining processes vary by region and supplier, the nature and intensity of odors can differ even between batches of asphalt binders. Other factors for odor mitigation assessment include the temperature at which the plant is operated, geographical attributes—such as hills and valleys—humidity, temperature, wind speed and direction, and proximity of neighbors.

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There are many potential VOC emission sources during the processes of refining the feedstock, manufacturing the mix, and storing the finished product. This is especially notable during the storage of bulk asphalt in a heated tank, in addition to stack emissions during production. Loading asphalt from one vessel to another—such as from the silos into trucks, and from trucks into a paver hopper—is another frequent odorous phase.

VOC concentrations increase significantly at higher temperatures. Below 150°C, few detectable VOCs are produced, but above this point, emissions increase. VOC prevalence is also dependent on the surface area of asphalt exposed to air over asphalt-coated aggregates. VOCs also increase substantially when these asphalt-coated aggregates are agitated.

Ecosorb’s vapor phase delivery system is useful for mitigating odors in airborne particulate matter at a baghouse.

Research-driven and plant-based solutions

Asphalt production variability spawns the need for adaptive and sometimes customized blends. Although there is no one-size-fits-all solution, there are general formulations that bolster odor mitigation efforts for a variety of asphalt mixes. These general formulations are added to the mixes to neutralize several odor-causing constituents, like hydrogen sulfide, mercaptans and general hydrocarbons. Specialty suppliers update their additives from year to year based on aggregate samples taken at asphalt plants to maintain effectiveness.

Although general formulations are efficacious for many mixes, some plants require custom blends, and expert suppliers can help with these needs as well. In these situations, asphalt samples are taken from the plant during multiple stages of production. These samples are then studied in a lab using gas chromatography mass spectrometry (GC-MS) to determine the precise molecular makeup of odors, even those present in minute amounts.

A GC chromatogram is a visual output of the data recorded by the detector, and it is presented as a plot of detector response along the y-axis, versus retention time along the x-axis (See the graph in this article).

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Each compound detected appears as a single peak on the graph, with the corresponding retention time value used for identification. Once the odor-causing compounds are identified, scientists develop a formulation using plant oils to molecularly neutralize the odors when the additive is combined with the mix.

This results in versatile and cost-efficient solutions—specially crafted for maximum effectiveness in each application—with each solution leveraging customized concentrations of plant oils, biobased surfactants and water to eliminate odors. These additives are designed to be safe, non-toxic and biodegradable, and to be applied during any phase of the asphalt lifecycle: manufacturing, storage, transportation and use. When used in refineries, hot mix plants, transportation systems and paving operations, they are blended directly into the asphalt mix (Figure 3).

These additives are also useful for mitigating odors and blue smoke when dispersed via vapor phase during the capture of particulate matter in a baghouse.

Airborne vapor phase dispersion is also commonly deployed to control odors at storage terminals, where asphalt is kept prior to delivery.

Multi-mix odor neutralization with a single additive

One longtime Ecosorb end-user customer—a new and reclaimed asphalt pavement plant producing 1,500-2,000 tons of hot mix asphalt each day for contractors and construction firms—relied on a basic odor-mitigating additive for years. However, recent asphalt mix variability spurred the need for a specially targeted formulation. The different mix sources and grades began producing pungent odors in the areas surrounding the plant, and the standard additive was no longer effective.

Spring Startup: Keep an Eye out for Blue Smoke and Odors Before Your Neighbors Do!

The plant shipped samples of three different asphalt mixes to Ecosorb’s lab to assess the levels of hydrogen sulfide, mercaptans and general hydrocarbons in each. The data from one asphalt mix, before and after treatment at 150°C is shown in Table 1.

Although the levels were different in each mix, the team of scientists formulated a single blend to neutralize odors in all three mixes, eliminating the burden of correctly matching different additives with a specific mix. The plant added this single blend to all its mixes, which reduced airborne sulfurous release by over 90%.

Ecosorb uses GC-MS instrumentation to identify odor-causing substances in asphalt mixes, and then develops custom plant-based formulas to neutralize odors.

Effective eco-products enhance odor abatement

By adding plant-based odor removers to asphalt mixes, manufacturers can effectively mitigate odors using safe, environmentally friendly and cost-efficient methods. These custom formulations do not mask smells, but instead mitigate them by breaking down and neutralizing odor-causing molecules in the mixes.

These mitigation techniques empower asphalt manufacturers to redirect their time from odor control and complaint handling, to maximizing production and overcoming the steady stream of challenges posed by evolving feedstocks.

Laura Haupert, Ph.D., is the chief scientific officer for Ecosorb, where she leads research and development, regulatory, safety and quality control. She earned her B.S. in chemistry from Manchester College and Ph.D. in physical chemistry at Purdue University, working with bond energies of solvated clusters. Haupert also completed her post-doctoral research at Purdue.

Editor’s Note: The team at Asphalt Testing Solutions & Engineering (ATS) prepared this guide to using asphalt modifiers in enhancing pavement performance based on Tanya Nash’s presentation of the same title at the National Pavement Expo (NPE) Jan. 23-25, 2024, in Tampa. The next NPE takes place Jan. 29-31, 2025, in Tampa.

Balanced mix design (BMD) is not just about performance; it’s also about being able to create an economical and sustainable pavement. Innovation is progressing faster than ever, trying to create this BMD. How do transportation personnel know what’s available on the market and better yet, how do they know it works? The modifier world is vast and can be confusing. Some examples of the categories and modifiers available are illustrated in Figure 1.

Modify means to make minor or partial changes to improve something or make it less extreme. What do you think of when you hear “modified asphalt?” Depending on your role in the industry, the answer may be different. The modification could pertain to the liquid asphalt binder or the asphalt mixture. No matter what your role, the goal of meeting the specifications is the same for everyone. (See the players in Figure 2).

SmartMIX Boosts Recycling Content in Balanced Mix Design

Why modify asphalt? One reason is due to higher demand on our pavements. The heavier loads and increased volumes create distresses that unmodified pavements cannot withstand. The goal of modification is to increase the service life of the pavement by addressing common failures such as rutting, moisture damage, raveling, cracking and bleeding.

Basic volumetrics of a mixture will only tell you so much about the long-term performance of the pavement. Waiting 10 years to determine if the mixture performed is impractical. But how do we determine which designs perform before we place them in the field? The balanced mix design process utilizes performance testing to try and answer this question and help us properly evaluate the different modifiers’ impacts on performance. When selecting the performance tests to use for the evaluation it is important that the tests and evaluation maintain three key ideas:

• Strong relationship to field performance
• Practicality: cost, time, complexity
• Repeatable, reproduceable tests

A balanced mix design (BMD), simply put, uses performance tests to help “balance” the mix’s resistance to both rutting and cracking. Mix designers and lab techs alike work to achieve the perfect balance of virgin materials, recycled ingredients, modifiers and so on, to get the optimum performance characteristics.

Another reason to modify asphalt is to address specification requirements. Specifications range from a recipe to performance driven specification. This creates either the “must use” modification or the need to use it to meet performance requirements. The key to the performance-driven specifications is to let the performance drive the innovation. Restricting the modifiers to a list starts falling back into a recipe type specification.

Think about the sustainability factors. It appears almost anything can be recycled into asphalt; is this true? While it’s important to consider the environmental aspects we do not want to sacrifice the quality or longevity of the pavement’s life. Sacrificing the pavement performance contributes to the environmental impact at the end of its service life. This may be greater than the benefit of using the recycled modification in the beginning. It is important that the entire life cycle is considered when making the decisions to use modifiers.

Is Your Lab Ready for Balanced Mix Design?

Economics also play a large role in asphalt production and paving. The value of asphalt modification is becoming more apparent, and agencies are starting to pay more for the increase in service life.

Even with these reasons, there are pros and cons of modified asphalt, such as those indicated in Figure 3. Let’s break them down next.

The next NPE takes place Jan. 29-31, 2025, in Tampa. Visit https://nationalpavementexpo.com/ for a recap of this year’s event and to see what’s coming up!

Performance

There are three factors to consider regarding performance: constructability, aging resistance, and rutting and cracking. Regarding constructability, some modifiers make the mix too stiff or viscous to compact or properly work by hand. They can also cause the mix to cool too quickly. However, other modifiers help in this area working as compaction aids or viscosity reducers.

Modifiers help the mix resist aging from oxidation. They can work as a “face cream” for the pavement as a surface treatment that reflects UV light. Modifiers can help with rutting or cracking, but it takes balance. Some modifiers will swing the pendulum too far one way or the other.

A balanced mix design (BMD), simply put, uses performance tests to help “balance” the mix’s resistance to both rutting and cracking. Mix designers and lab techs alike work to achieve the perfect balance of virgin materials, recycled ingredients, modifiers and so on, to get the optimum performance characteristics.

Specs

Quality assurance (QA) is vital to modified asphalt. We learn what is in the binder by testing and performing QA. Performance testing has evolved to include many tests used to verify different performance properties of the liquid or the mixture to differentiate non-modified and modified asphalt. Many modifier suppliers have completed initial lab and field evaluations in conjunction with state departments of transportation (DOTs) willing to work with them to construct, monitor and evaluate these test sections.

Specification updates are crucial as technologies are developed. As mentioned before, some owners are writing recipe specifications that may require modification or some specifications have performance driven criteria using BMD.

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On Sept. 27, 2019 (effective Oct. 28, 2019), based on a century old Federal requirement, the outdated requirements in 23 CFR 635.411(a)-(e) were rescinded to encourage innovation in the development of highway transportation technology and methods. State specifications have been rewritten to replace words such as “exclusively” and “shall be produced with” which restrict producers and suppliers to innovate with new products and possible performance enhancers and cost savings.

Approved product lists (APL) traditionally approved products with decades old processes, and some have not been adjusted as new tests and products have evolved over time. With the mindset of driving innovation, many states have developed an innovative products list (IPL) that identifies products under consideration by the department that may not fall into a current APL category.

Further complicating quality control (QC) testing is defining the terms of acceptance of a mixture under performance testing. As the tests have progressed and the industry is using more of them, most are still looking at different ways to accept and pay for mixtures using these results.

The key to the performance-driven specifications is to let the performance drive the innovation.

Recycled Materials

Using more recycled materials is environmentally friendly, but this means less new materials are being introduced into the mix. To address this issue, modifiers have been developed specifically to mobilize or rejuvenate the aged binder of RAP and RAS.

Cost

Cost is always at the top of everyone’s mind. Modifiers can help with cost in that they can aid in virgin binder replacement, find effective use for waste materials, increase the use of recycled materials and provide a life cycle extension.

Applying these ideas relates to BMD. Danny Gierhart, P.E., at Asphalt Institute, has stated BMD is “asphalt mix design using performance tests to help balance the mixture’s resistance to rutting and cracking.”

Balance Your Mix Design for Asphalt

BMD offers paths to promote innovation while meeting performance expectations, offering an opportunity for modifiers to play a vital role in the future of asphalt mixes. Modifiers bring valuable and innovative solutions that can help overcome deficiencies in the binder and the mix. They can be cost-effective and sustainable. Knowledge is key and collaboration between agencies, contractors and suppliers drives innovation. It is important for specifications to promote innovation, not prevent it.

Roads are a capital investment, and we must take a proactive approach to protect this asset. Applying the correct modifier in the appropriate scenario can help enhance pavement performance as well as extend the longevity of our roads.

Tanya Nash is the director of engineer at Asphalt Testing Solutions & Engineering (ATS), an approved Florida DOT Construction Training Qualification Program (CTQP) instructor and 2024 president of the Association of Modified Asphalt Producers (AMAP).