Avoid WMA Roadblocks, Reap WMA Benefits
BY Sandy Lender
Your plant may use a mechanical foaming process or a chemical or plant-based additive to produce warm-mix asphalt (WMA) mixes. Either way, the end goal for producing a WMA pavement mix can be multifaceted. The asphalt industry has, as a collective, learned of multiple benefits of producing and placing WMA. If you’ll pardon the pun, some of those benefits are seeing roadblocks.
For example, you don’t necessarily want to change out mix designs four and five times a day. This means Producer ABC may elect to run the easy mix with no WMA technology if he doesn’t have to use a more complex design on a given day. Unfortunately, this means he doesn’t get the extra energy and environmental benefits of the technology that day that he already enjoys as an asphalt mix producer.
There’s a reason he might choose avoidance, you see. Switching mix designs throughout the day might be cumbersome if he doesn’t have the right equipment for the job. Cost is a roadblock if the department of transportation isn’t willing to offer an incentive for trying out a new process, new additive, new blend, etc. Running a WMA all day isn’t worth the hassle if not all of his customers and their inspectors are willing/able to understand the temperature differential. You get the idea, so let’s look at what some experts in the industry have to say about overcoming the roadblocks to reap the benefits of WMA production.
When producing WMA pavement mixes, you lower the temperatures with which you’re working, thus the temperatures of the final products. As asphalt mix producers know by now, lower production temperatures result in decreased fuel consumption, less energy use, fewer emissions possibilities and better air quality overall.
Vice President of Engineering Mike Varner at Astec Inc., Chattanooga, shared that the trend in the use of additive technologies in particular shows “[t]he industry is willing to accept and continue to test and use new technology; there remains momentum towards reducing fuel consumption by lowering mix temperature, which in turn lowers both process and fugitive emissions; and additives often are capable of going lower in temperature than mechanical foaming.”
Those particular benefits are happening, obviously, at the plant.
When we look at the paving train, we often see ease of movement and ease of compaction with WMA pavement mixes. One of the constant benefits out in the field is the continued performance of the mix after long haul times and during cooler ambient temperatures of early spring and late fall. Varner suggested: “In the case of mechanical foaming, with the technology—being relatively low cost—there is a tendency to use it as a compaction aid, which is good.” He pointed out that some contractors are prone to use that benefit without lowering temperature, though, which is a positive for compaction, but does not help fuel consumption or emissions.
These benefits overall make the use of WMA a no-brainer, right? Dennis Hunt, the senior vice president of Gencor, Orlando, pointed out a majority of producers who run WMA do so with foaming equipment. “From the foaming perspective, it works,” Hunt said. “It’s tried, it’s true, it’s proven.” The use of mechanical methods—and other methods—is proven by the most recent National Asphalt Pavement Association (NAPA) Asphalt Pavement Survey on Recycled Materials and Warm-Mix Asphalt Usage (Information Series 138), which the team at NAPA shared in Figure 1.
With proven technologies in place, roadblocks seem illogical. What’s happening may be deemed bureaucratic or financial, but there are options for success in the ongoing WMA trends.
Specs and Sense
Hassan Tabatabaee, Ph.D., the global technical lead at Cargill Anova Asphalt Solutions, headquartered in Minneapolis, shared that the low-bid specification system, when coupled with a lack of performance-related incentives, has hindered the growth of WMA use. Now, this is in relation to chemical WMA production, which carries a price-per-ton the mix producer must pass on to the agency/owner.
Tabatabaee prepared a written statement: “In the current industry environment, often there is little economic incentive to use WMA unless mandated, as contractors often cannot afford to use these additives solely for their sustainability benefits.”
Lance Brooks, sales manager at Ingevity, North Charleston, South Carolina, explained, “Agencies look for quality mixtures that perform well. Contractors look for technologies that are easy to use and have proven performance.” Since 2004, WMA technology provider Ingevity has demonstrated how customers can benefit economically from the comprehensive benefits of warm mix across all 50 states and multiple countries. The company’s Evotherm® additive is designed to enable contractors to consistently meet specifications for density, for example, in addition to offering other environmental and performance-related benefits.
“In general, most customers are looking for help in improving the ease of mix compaction on the grade with the mix temperature that of traditional hot mix temperatures,” Ivann Harnish said. He’s the commercial director for Road Science®, a division of ArrMaz, located in Tulsa, Oklahoma. “There is little interest in decreasing mix and compaction temperatures. Among contractors, it’s about achieving density more easily, faster and consistently.” He believes in the use of Road Science’s AD-here® ULTRA line of WMA additives, which combines a compaction aid and adhesion promoter additives, to help contractors achieve target densities more easily.
“A recent trend in WMA additive technology is the rollout of products that offer secondary features such as compatibility with a wider range of asphalt modifiers, and features related to improving plant and paving crew comfort and safety by reducing odors and the health hazards associated with the additives themselves,” Harnish said. “This is a trend in the right direction because it not only offers terminals and mix producers greater additive versatility, but also safeguards the hardworking industry workforce we rely on to build and maintain our infrastructure, and keep the goods and services that power our economy moving.”
Odor suppressants join the rejuvenators and anti-stripping agents on the market today.
“Many current and emerging technologies, such as new warm-mix additives and rejuvenators, rely on precise introduction of liquid additives at the hot mix plant into the asphalt binder prior to injection into the drum,” Tabatabaee shared. “Therefore, asphalt producers will be well-served by incorporating versatile additive injection systems (i.e. capable of running anywhere between 0.1 to 3 gallons per minute), and additive tanks at their asphalt plants. Furthermore, as the performance hurdles to use of higher recycled content in HMA decrease—due to emergence of new additive technologies—producers will be well served by investing in removing operational hurdles to reliable use of higher recycled content, such as upgrading drum flighting, expanding RAP blend sizes, and RAP fractionation capabilities (See articles on how to implement these concepts at www.TheAsphaltPro.com).”
One of the companies that has provided producers the ability to jump over performance hurdles is Stansteel®, headquartered in Louisville. CEO Lennie Loesch spoke of the evolution of “green” WMA kits over the years. His company “went about developing an engineering system for what we call ‘dynamic foaming’ resulting in proven warm-mix technology…”
What his team developed was a dynamic foaming system with a number of elements that could mix liquid—whether water or other chemicals—with the liquid asphalt and avoid laminar flow in the piping system of the combined material, Loesch explained. “As with combining any other ingredient with either the liquid asphalt or the hot mix, it needs to be proportioned precisely, accurately, repeatably and variably based on different production rates, different tons per hour and different percentages of the base AC required. Therefore, the Stansteel design of the Accu-Shear® Dynamic Foaming System took all of these factors and more into account when configuring all of the equipment that was needed. Stansteel/Hotmix also provides a sampling device [which situates inline] after combining the liquids to prove that expansion and foaming have dynamically occurred.”
Loesch pointed out that as chemical companies find favor with government agencies, “there are going to be a number of chemicals that are added to the hot mix and, rather than producers fight it, they will adapt and charge more for their mix because the government specifying agency calls it out in the specification.”
On the other hand, for private mixes, savvy producers will likely elect to run a less-modified mix—one with fewer additives, thus lesser cost.
“Because this was anticipated an upcoming factor, the Stansteel Accu-Shear was developed to handle combinations of liquids or multiple materials at the plant.” Loesch said. “In some cases, there are five or six different liquids that can be easily switched back and forth, depending on what was specified by the agency.
This could be a liquid chemical, a cutback liquid, or water foaming. This is done seamlessly through a combination of the pumping and metering systems blending the Accu-Shear and then dispensed with liquid asphalt to mix properly with the liquid and subsequently coat the aggregates, recycle, dust and more.”
“Advances in asphalt technology have the potential to deliver benefits to us all, but we can only realize those benefits if we adopt a more forward-thinking approach to asphalt design,” Cargill’s Tabatabaee also shared. “Leading research institutions are making significant investments to support this change, as we are beginning to see progressive state transportation agencies experiment with new performance-based approaches.” (See our article on Balanced Mix Design).
Consider the efforts from industry and agencies for the success of warm mix. These days, DOTs often allow the use of WMA to be a contractor option. Does Producer ABC want to produce a WMA for all of his customers on a given day? He may get his best performance when doing a long production run of one mix, but he must take all of his customers in to consideration. Not all customers understand—or have been educated on—the benefits of the warm mix product. If he has not educated all customers on its benefits, the FOB customer may be concerned about low temperatures, and so on. Producer ABC will want to have technology in place to switch mixes easily, letting him switch between mixes more easily to accommodate multiple customers while gaining the benefits of warm mix as often as he can.
As Tabatabaee pointed out: “…within the low-bid, specification-driven U.S. system, there are tangible economic benefits to using WMA as hot-mix compaction aids, helping contractors achieve density bonuses, especially in colder climates, and when used early and late in the paving season….The recent trends toward development and adoption of performance based balanced mix designs and specifications offers an opportunity for agencies to incentivize trial and introduction of innovative technology such as rejuvenators and alternative warm-mix technology, while limiting their exposure to risks of failure.”
As mentioned above, rejuvenators add another element to the story. Their purpose is to restore properties to the aged, oxidized binder in the reclaimed material, be that reclaimed asphalt pavement (RAP) or reclaimed asphalt shingles (RAS). By softening or restoring the “hardened” binder, rejuvenators can make it possible to get more effective use of the binder.
“Another area related to a trend is the development over the last few years of rejuvenators,” Loesch shared. “These rejuvenators are properly added and metered and proportioned to the amount of RAP or shingles that are added to the mix.” In the early days, Loesch remembers, some producers were encouraged to merely spray rejuvenators into the base of the slat conveyor or onto the recycle belt or stockpile. “Of course, this…did not account for any irregular coating or for any changes in production rate or in percentage of RAP or RAS added to the material. The Stansteel team has designed over 45 different combinations of pump skids and metering devices for these rejuvenators and other liquids. One size does not fit all.”
To get mixes right-sized and on-trend, producers can turn to any number of OEMs for storage options and blending units. It’s wise to start with the additive supplier, as you’ll learn next, to ensure all materials will be compatible with all seals and components.
“With the advent of the Accu-Shear Advanced unit, many customers are choosing to create their own PG grades by on-site blending,” Loesch said.
Road Science’s Harnish said, “For mix producers who are thinking of using and storing a WMA additive, it is of the utmost importance that they consult with their additive supplier to fully understand what types of storage tanks, pumps, gaskets and line materials are recommended for proper additive storage and handling. You want to make sure that your equipment is suitable to ensure ease of handling of the additive, and that the materials are compatible with the additive chemistry to avoid other issues from arising.”
Astec’s Varner said, “Most of the technologies have now been sufficiently engineered so as not to have significant impact on plant components and processes. The best technologies take plant configurations and processes into account so that the introduction of the technology is no more difficult than delivery of any other additive. Frankly, the onus is with the technology provider to minimize the need for plant personnel to accommodate the technology.”
Be that as it may, there are combinations of technologies and materials coming into vogue. Loesch pointed out: “For any combination of reasons, it seems as if there are more and more government specifying agencies that are requiring many different grades of liquid AC. We have had a report from one state that, for a given location, the state is requiring 11 different PG grades of asphalt. Now, let’s say each of the grades would require a chemical additive added at the asphalt terminal; does that mean the asphalt producer will need 22 to 25 different liquid AC storage tanks?”
Stansteel’s liquid AC plant site blending experts suggest using the Accu-Shear to add latex or other additives to create multiple PG grades at the plant. “This has multiple benefits in that [the producer] is creating [the blend] in a very accurate manner and does not have a chance for many of the ingredients to settle out, since agitation is also required for many of the chemicals and additives that are combined with the liquid AC,” Loesch said.
“Another huge benefit is that they only create the amount needed and more expensive PG grade asphalt does not have to be wasted on jobs just because that is what is remaining in the AC tank. Of course, another huge benefit is that the producer does not have to buy three, five or 10 more AC tanks to store all the different liquids as required by the government specifying agency. Just the capital cost alone with the maintenance and heating costs and more could be prohibitive.”
Ingevity’s Brooks explained further: “In general, DOTs and agencies test for rutting, cracking and moisture resistance in their pavements. During the construction process, consistent compaction (density) is critical for contractors. An additive like Ingevity’s Evotherm allows agencies and contractors the ability to achieve these goals while seeing the added benefits of the lowest temperatures, ease of use, and proven performance.”
He reflected on the past and the future of WMA: “Over the last 15 years, we have seen an increase in the adoption of WMA by agencies, as well as increased contractor usage of the technology. It is exciting to see WMA enable contractors and agencies to achieve their goals.”
Aspects of WMA’s history and basic componentry can get lost over the years. Let’s take a quick look back at the concept’s fame.
NAPA included a press release on its website when the industry won a Construction Innovation Forum (CIF) NOVA Award in 2013 for its work to speed the deployment and uptake of WMA. Formed in 1987, CIF is an international, non-profit organization that encourages and recognizes construction innovations. CIF created the NOVA Award in 1989 to recognize and advance significant innovation in all areas of the construction industry around the world. Nominations come from all segments of the industry and represent the efforts of owners, contractors, architects, engineers and others to improve the industry. The award nominations represent proven cost savings and quality improvement on actual projects.
NAPA stated WMA encompasses a range of technologies used to reduce the production and placement temperature of asphalt pavement mixtures. According to the Federal Highway Administration’s Every Day Counts program, the reduction is 30-120oF below traditional HMA. According to the CIF NOVA Award official video presentation, the reduction is 30-75oF below traditional HMA.
NAPA continued, stating, a variety of environmental, worker safety, and construction benefits have been realized through the adoption of WMA. It was introduced to the United States from Europe in 2004. Since that time, the United States has become the leading adopter and proponent of the technology. By 2010, the FHWA named WMA as an Every Day Counts initiative as a proven technology with environmental and construction benefits. In selecting warm mix to win a 2013 NOVA Award, the investigators cited its ability to improve compaction, reduce fuel or energy use, improve worker comfort, lengthen the paving season, and reduce overall paving costs.