Infrastructure issues such as crumbling roadways continue to plague the United States. According to the American Society of Civil Engineers, one-third of our major roads are in poor or mediocre condition, earning America a dismal “D” on its 2013 Report Card for America’s Infrastructure.
Road repairs, however, are complicated by limited budgets in the Department of Transportation (DOT). Consequently, DOT customers are especially attracted to solutions that deliver more performance and miles of pavement with less investment and maintenance. At the same time, they want the job done faster to keep our roadways open and taxpayers happy.
Road contractors are hard-pressed to deliver against those competing needs, and rely on improvements in technology – both equipment and materials – to help make a difference. One solution getting more attention is a new generation of asphalt additives, such as those from Honeywell, that help drive up performance and drive down costs, delivering more with less – and fast.
About 93% of the 2.6 million paved roads in the U.S. are surfaced with asphalt. Hot mix asphalt (HMA), which is comprised of rocks, asphalt binders and air voids, is engineered to handle a diverse range of traffic loads and stresses. Next-generation asphalt additives are designed to improve strength and durability, boosting HMA performance even more.
Laboratory testing by the University of Wisconsin-Madison, and results from various paving projects, demonstrate how next-gen additives dramatically improve rutting resistance by up to 30% and low-temperature cracking strength by up to 40%.
As shown in Figure 1, these benefits are due to a unique aggregate distribution. Next-gen additives are able to increase the total contact length between rocks in the asphalt mix. This improves aggregate packing and distribution, enhancing load-bearing properties, durability and road performance.
Contractors can build roads faster due to improved workability, which translates to less compaction effort and fewer roller passes. Projects can be completed sooner and use lower paving temperatures, saving millions in fuel costs while lowering emissions and extending the paving season.
Figure 1: Better Contact Length Improves Performance
Slash maintenance costs by 35%
As mentioned, next-gen additives enable the paving of stronger, longer lasting roads at currently specified thicknesses. A longer lifetime, in turn, translates to fewer maintenance cycles and costs. In fact, the maintenance cycle can be cut by up to 50%, as shown in Table 1.
Industry models show that road maintenance is required every six to seven years – or at least six maintenance cycles over 50 years. Next-gen additives, however, can cut the number of cycles down to three, reducing road life costs by 35 %. This is calculated by the following equation, which assumes a 50-year road life and factors in additives costs:
Initial Road Cost / Mile + (Total Number of Maintenance Cycles X Cost/Mile for Each Maintenance Cycle)
These savings can free up dollars for other road builds and maintenance projects.
Table 1: Cut Maintenance Cycles by 50 % and Costs by 35 %
Pave up to 40% more miles
Next-gen additives also enable roads to be paved at about half the thickness of today’s roads, but with equal or better performance. As illustrated in Figure 2, a typical wearing layer of four inches can be reduced to 2.2 inches – a reduction of 45%.
This means that more miles can be paved with every dollar at a reduced cost, stretching the paving budget. Table 2 shows how 43% additional miles can be paved at a 45% savings in HMA material costs, leading to a 30% savings in total cost per mile. This is calculated by:
Today’s miles paved – Miles paved using Honeywell’s next-gen additives / Today’s miles paved
Today’s HMA material costs – HMA material costs using Honeywell’s next-gen additives / Today’s HMA material costs
Today’s total cost per mile – Total cost per mile using Honeywell’s next-gen additives / Today’s total cost per mile
As an example: for 32,000 lane-miles, this frees enough funds to pave nearly 14,000 more lane-miles annually than the typical HMA formulation.
Figure 2: Reduce Top Road Layer By Up to 45 %
Table 2: Stretch Paving Miles by >40 %
One large metropolitan city on the West Coast of the U.S. was experiencing excessive wear and tear in the form of rutting and potholes due to heavy traffic volumes. They needed an HMA that could deliver better performance with their existing budget.
When a next-gen Honeywell additive was added in small quantities (0.05% to 0.2%) to the HMA, the modified HMA delivered the following results:
- Only 1 mm rutting after a full 6,900 cycles versus the control HMA’s failure after only 1,800 cycles per the Pine Rut tester.
- Increased recycled/reclaimed asphalt pavement (RAP) from 20% to 25%.
- Estimated pavement life extended from seven to 12 years – a 71% increase – per AASHTOWare* Pavement ME Design analysis based on 0.25 inches rutting failure.
The city subsequently chose the Honeywell modified HMA and expects it to deliver more durable, longer-lasting roads requiring fewer repairs in the future.
Advantages to contractors
The performance and application advantages of next-gen additives enable contractors to operate at the forefront of technologies that address the competing challenges of building roads more economically, yet with the same or better road performance.
With next-gen additives, contractors now have more options. They can, for example:
- Build longer lasting roads at currently specified thicknesses, significantly reducing maintenance costs over the lifetime of the road.
- Build better roads at a reduced thickness, saving on materials while maintaining performance.
- Get jobs done faster through improved productivity.
- Get more jobs with an extended paving season.
- Reduce fuel use and emissions, addressing air quality concerns.
Such advantages can help improve customer satisfaction and loyalty.
Driving success forward
Despite the need to move forward with innovative technologies like next-gen additives, actual implementation can encounter roadblocks. Today’s road specification standards, for example, tend to specify a single pavement thickness regardless of the material and may not accept newer design models. Yet laboratory testing and industry-defining software, such as the AASHTOWare Pavement ME Design, all suggest stronger materials can indeed deliver the same or better road performance at a lower thickness.
Such restrictions need to be lifted so that road designers have the flexibility to specify performance and thickness based on the proven strength of advanced materials. Not only will contractors benefit as described above, but DOTs will be able to:
- Get more miles out of every dollar while maintaining or improving road performance.
- See more miles paved in less time, opening roads faster.
- Address growing public concerns about road quality and the desire to see their tax dollars put to good use.
Next-generation additives are already delivering results. Improving our roadways can be accelerated, however, by updating specification standards, testing and modeling in ways that open the door to innovative solutions.
Cindy Kostelansky is the marketing leader for asphalt at Honeywell. She holds a Ph.D. in inorganic chemistry from the University of North Carolina at Chapel Hill, and completed her postdoctoral research in catalyst development at the U.S. Naval Research Laboratory in Washington, D.C., where she received the National Academy of Sciences Post-Doctoral Research Fellowship. She holds four patents and is an active member of the Asphalt Institute, NAPA and other professional organizations. She is based in Morristown, NJ.
*American Association of State Highway and Transportation Officials