Bridge Sustainability and Performance Within Asphalt
BY Ryan Lynch
The full picture of cradle-to-grave emissions reduction includes wise use of quality recycled asphalt materials
As we look toward the future of surface transportation construction specifications, one thing is certain: change is coming. Specifically, environmental product declarations (EPDs) and product category rules (PCRs) are going to be critical components of change in the road-building process. When, where and exactly how are the big unknowns for many of us, whether we are owners, suppliers, producers or other industry-connected organizations and individuals. Specifically, the initial focus on cradle-to-gate metrics rather than a complete cradle-to-grave analysis has many of us pausing and wondering how this will translate into durability and quality of our roads.
However, one encouraging aspect of this otherwise uncertain future is the many existing products available to asphalt road builders and raw material suppliers that bridge the gap between these sustainability goals and legitimate long-term durability concerns. These products are often as cost neutral as they are carbon neutral, and in almost all circumstances, they provide net benefits to the performance and durability of our asphalt pavements.
Bio-based modifiers and recycling agents (often referred to as rejuvenators) are good examples of this, such as the Invigorate® and Invigorate Plus® lines of products offered by Colorbiotics, a Sika Company. These products—and products like them—have been part of our pavement ecosystem for the better part of a decade and have demonstrated the ability for pavement designers and builders to maximize recycled asphalt materials (RAM) without sacrificing performance. Many of these products, including Invigorate and Invigorate Plus, are USDA Certified Biobased.
“Change is about the narrowest and hardest groove a man can get into.”—GK Chesterton
What’s interesting about the development of these products is that they sprang up largely as rheology modifiers for asphalt refiners and suppliers, chosen solely for their efficiency and overall effectiveness in improving performance properties of asphalt binders.
Let me reiterate that point another way.
Refiners and asphalt suppliers, already entrenched in the supply chain for petrochemical products like aromatic and paraffinic oils—long used as asphalt binder extenders—looked outside that sector to explore new ways to improve their binders. At the time, due to the emergence of cokers, variability in crude supply and the resulting refinery economics, producing consistent, high-quality, performance-grade asphalt began to be more difficult.
Faced with these challenges, they turned to other petroleum-based modifiers to help them manage the quality of their asphalt. As I will detail shortly, those were not always ideal options, so they kept searching for alternatives, some of which were these bio-based modifiers.
They discovered very quickly that these bio-based modifiers were the answer they had been searching for. In most cases, the bio-based alternatives were more cost-effective and also avoided several health, safety and environmental (HSE) concerns that came along with these petrochemical oils, most notably their effect on mass loss.
On top of this, binder performance most often decreased by using these traditional petroleum-based products. Sure, you could soften binders and provide a more diverse product slate, but a quick analysis of binders—whether it be by Delta TC or Glover Rowe—often showed the resultant binders to be of lesser quality. Further aging studies even pointed to the susceptibility of worse long-term aging with binders containing these additives.
With bio-based modifiers, not only could you safely drop grades, but you could do it in a way that binder properties improved, even in long-term aging studies. Furthermore, these bio-based modifiers were found to be extremely compatible with the growing variety of asphalt streams around the country, as well as popular modification materials like SBS polymers. In fact, studies showed polymer solubility and crosslinking improved when these modifiers were present in the asphalt cement.
The more efficiently modified AC binder also delivered cost savings to suppliers, and by extension, producers and owners. A single supply point that could only provide one grade prior to modification was now providing several. That saved on freight and improved the quality of the asphalt stream since there was no longer a concern about the negative effect on quality of petrochemical modifiers.
All of this, of course, led to improved performance properties of the overall asphalt pavement. As you improve binder quality and overall softness, it helps counteract the embrittlement that occurs when you raise RAM content in a mix, effectively inundating it with age-hardened binder. This allowed users to start designing more sustainable and cost-effective roadways by boosting RAM content in their specification, while mitigating any performance issues they would see without the use of these bio-based additives.
This was all a result of basic business optimization by suppliers and refiners. The entire innovation occurred before anyone in the paving industry was using acronyms like EPDs or PCRs. However, since those two acronyms seem to come up in any conversation about asphalt pavements, it is comforting to know that in these additives there exists an opportunity for a massive win-win situation.
That win-win situation also fits nicely into the cradle-to-gate PCR the National Asphalt Pavement Association (NAPA) has put together. Let me briefly explain how:
- As noted, these additives are engineered from by-products of renewable energy technologies, lowering the carbon footprint of any asphalt mix where they are incorporated.
- With products like Invigorate and Invigorate Plus, producers can use them as warm mix additives as well, decreasing carbon emissions at plants by dropping production temperatures by as much as 50°F.
- Emissions are further reduced because the asphalt binder doesn’t have to be transported as far due to the supplier’s ability to use these bio-based modifiers to expand their product slate in closer terminal locations.
- These additives enable the use of more RAM, reducing the amount of virgin aggregate that has to be excavated, processed and transported to the plant site. This also contributes to a reduction in emissions.
- Additives like Invigorate and Invigorate Plus aid in compaction and obtaining density in pavements at lower ambient and mat temperatures, which increases the haul distance from fixed and mobile plants. That eliminates the carbon-laden mobilizations of these plants.
All these benefits can be realized in this first phase of NAPA’s PCR, a phase that has not yet weighed in on the environmental impact from the gate-to-grave, but their benefits extend far past that first milestone. Again, that stage is of particular concern to owners who are justifiably worried about the long-term durability of new pavements that were designed to meet these sustainability and reduced carbon emissions goals. As it turns out, they need not worry, as that is where these bio-based modifiers like Invigorate and Invigorate Plus shine as well.
Largely due to balanced mix design (BMD) efforts, but also due to the past innovation plays by refiners and suppliers, we have a very good idea of how these pavements—with increasing amounts of RAM, bio-based modifiers and recycling agents—truly perform. Tens of millions of hot-mix asphalt (HMA) pavements already contain these additives. And we have lab and field performance data from a variety of locations.
In all circumstances, testing with methods like Hamburg Wheel or IDEAL-CT on aged mixes shows increased performance versus control mixes not containing these bio-based modifiers. Extracted binder properties are improved as well, just as they are seen to improve virgin binder rheological testing. The National Center for Asphalt Technology has several sections containing these additives that show similar results.
So, as astonishing as it sounds, what we really have here is a “win-win-win” situation. Not only will these additives help us meet our sustainability goals, they will improve our pavements as well. Conveniently, the testing methodology innovations already being implemented into our industry are also extremely adept at evaluating the performance benefits these very additives provide.
It seems like we have a long way to go in bridging the expanse between a net zero carbon emissions future and the present need for upkeeping and even upgrading a surface transportation system. Our regulatory mechanisms and tools are still a long way from being finalized and implemented. Uncertainty, a bit of confusion and even an overall concern for the health of our roadways seems to be as prevalent today as it has been at any time in the past. Change always raises these types of concerns. It truly is the hardest and narrowest groove to enter. But enter we must.
Facing the understandable concern for the future, all of us in this industry—no matter our roles—can take comfort in the fact that we already possess the tools to bridge that gap between sustainability and performance. The difficult entry into this change has already been charted for us. We just need to decide as an industry to forge ahead, utilizing these innovative products confidently. The result is all but certain if we do: roads stretching through our environment, built with sustainability AND performance in mind.
Ryan Lynch
Ryan Lynch is the national sales manager, Colorbiotics Asphalt Solutions. He grew up in a family construction business and has spent his professional career in positions at every level of the asphalt industry.