Introduction
In the quest to produce cleaner fuels and maximize gasoline and diesel output, oil refineries have dramatically changed their processes over the past few decades. These advancements have yielded great benefits in fuel supply and environmental performance, but they come with an unintended consequence: the leftover material used to make asphalt for our roads is not what it used to be. Asphalt binder - the black, sticky glue in pavement - is now often a byproduct of intensive refining rather than simple distillation. Public works professionals are observing that today's asphalt doesn't seem to last as long; pavements may crack or age faster than in the past. To understand why, we need to explore how modern refining techniques have altered asphalt binder composition and what that means for pavement life. We will also look at real-world impacts on road durability and discuss practical solutions (from polymer additives to new surface treatments) to ensure longer-lasting roads.
Evolution of Oil Refining and Asphalt Production
Traditional vs. Modern Refining: In the early days of petroleum refining, producing asphalt was straightforward. Crude oil was distilled, and the heavy residue left at the bottom of the distillation tower became asphalt cement for paving. Refiners did relatively little beyond separating light fuels from heavy oils. The process left plenty of the complex, high-molecular-weight hydrocarbons in the residue - perfect for binding road aggregates. However, as oil demand grew and technology advanced, refineries introduced processes to squeeze more high-value fuels out of each barrel of crude. Today's refineries are often described as “unleaded gasoline factories,” focused on maximizing fuel. Gasoline, diesel, and jet fuel are the primary outputs, while asphalt has become a minor side-stream product in the refining. In fact, asphalt binder might constitute only ~2% of a refinery's output by volume, reflecting its comparatively low economic value in the refining balance.
Increased Fuel Yield & Cleaner Fuels: Over time, numerous advanced refining techniques were added to process the heavy fractions that used to go directly into asphalt. Starting around the mid-20th century, refineries adopted catalytic cracking - a process that breaks large hydrocarbon molecules into smaller ones using heat and catalysts. Catalytic cracking (e.g. in a Fluidized Catalytic Cracker, or FCC) targets the heavy oils (vacuum gas oils) and converts a portion of what would be residual material into more gasoline and diesel. Later, hydroprocessing methods (such as hydrocracking and hydrotreating) were introduced to further treat heavy oil under high pressure hydrogen. Hydroprocessing can crack heavy molecules and also remove impurities like sulfur and metals to meet clean fuel standards. While these processes are great for extracting every possible drop of fuel and meeting regulations for ultra-low sulfur fuels, they inevitably reduce the quantity and alter the chemistry of the residual oils that become asphalt. Simply put, modern refining is so effective at breaking down crude oil that far less of the original “heavy” content remains untouched to serve as durable pavement binder.
What Changed in the Asphalt Feedstock: In older refining operations, the asphalt binder was essentially the unrefined bottom of the barrel - rich in large, complex molecules (asphaltenes and resins) diluted with some lighter oily components (maltenes). Modern refineries, however, often go a step further with the heaviest fractions. Some use solvent de-asphalting units, which extract valuable oils from vacuum residuum and leave behind a very hard asphalt-like substance (sometimes called “pitch”). Others employ coking processes that thermally crack the heavy residuum into lighter hydrocarbons and solid coke, leaving minimal liquid for asphalt. The net effect is that the residual material designated as “asphalt” is now harder and more depleted of certain malleable components than it was in the past. Refiners also tend to blend different crude sources and refined streams to meet specifications, which can introduce variability. Many veteran pavement engineers will affirm that the quality of asphalt cement is heavily influenced by both the crude oil source and the refinery configuration - and those factors have been in flux. As refineries process a wider range of crude types and push heavier feeds through aggressive upgrading units, the composition of paving-grade asphalt binder has inevitably shifted.
Advanced Refining Techniques and the Loss of Key Asphalt Components
Modern refining techniques like catalytic cracking, hydrocracking, and others have a specific aim: remove or convert heavy complex molecules into something more valuable. This is great for fuel production, but for asphalt it means many of the components that once lent durability to binders are being stripped out or chemically altered. For instance, hydroprocessing tends to saturate aromatic rings and can remove polar compounds - in essence, it takes some of the “stickiness” and flexibility out of the asphalt residue. One way to think of asphalt binder is by its fractions: it contains asphaltenes (very large, hard molecules) and maltenes (oily constituents made up of saturates, aromatics, and resins). A good paving asphalt has a balanced ratio of these fractions. The maltenes act as a softer phase that keeps the binder viscoelastic (able to flex and heal), while the asphaltenes provide stiffness and body. Advanced refining can upset this balance.
Studies have found that excessive removal of maltenes during heavy-oil upgrading leads to a binder with abnormally high asphaltene content, which makes it hard and brittle. Essentially, when refineries extract too many of the “functional oils” from the residuum (to convert into more fuels or lubricant stocks), the remaining asphalt loses workability and ductility. Vacuum tower bottoms (VTB) or vacuum resid that have been through extensive processing can be so stiff that they resemble solid tar and would crack if used straight on a road. In fact, researchers note that these advanced-refining byproducts behave a lot like highly aged or oxidized asphalt - they lack the lighter fractions that allow asphalt to flex, making them prone to early cracking.
Another change is the increased presence of non-polar, waxy components relative to the aromatic resins. Asphalt chemistry is complex, but one simplified view is to categorize molecules as polar (which interact and form an elastic network) and non-polar (which form the viscous, flowable phase). A well-performing binder needs a good mix of both. If a binder has too many heavy non-polar molecules (for example, some high-molecular-weight saturates), it tends to have poor cracking resistance. This is exactly what can happen when refining processes reduce the aromatic, polar fraction: the binder can become dominated by hard paraffinic compounds that make it susceptible to thermal cracking. Modern hydrocracked or blended asphalts have sometimes been observed to have a lower “colloidal stability,” meaning the asphaltenes are not as well peptized (kept in suspension by maltenes) and can cluster, contributing to brittleness.
It's worth noting that refinery adjustments for cleaner fuels (like deep hydro-desulfurization to remove sulfur) also play a role. Desulfurization and hydrogen-addition tend to increase the saturation of the residue. The push for low-sulfur diesel and fuel oil in the 2000s meant many refineries had to more aggressively treat the heavy oil. An unfortunate side effect is that certain sulfur compounds and aromatics that weren't a problem in asphalt (and may even have contributed to its performance) are reduced, while the remaining product can be harder to work with. As one industry source summarized, “as the technologies for extracting valuable oils from crude are upgraded, the quality of asphalt binders is also degraded”. This is now a growing concern in the pavement engineering community - we're effectively getting a drier, more brittle glue to build our roads.
Impact on Asphalt Binder Performance and Pavement Life
What do these changes mean for the roads? In practical terms, modern asphalt binders can be more prone to aging, oxidation, and cracking than the binders of the past. A pavement's lifespan is largely determined by how long the asphalt binder can retain its flexibility and adhesive properties before it becomes too brittle. All asphalt will oxidize and harden over time - this is a natural process where exposure to oxygen causes the molecular structure to change (forming more stiff, oxygen-linked molecules). However, when a binder starts off with fewer protective oils and more brittle fractions, it reaches the “brittle point” sooner in its life.
Asphalt professionals have long observed the effects of oxidation: a freshly laid asphalt road is jet black and resilient, but with years of sun, air, and stress, it turns gray and develops cracks. The science behind this is that as asphalt oxidizes, it loses volatile components and its asphaltene fraction increases, making it stiffer and less able to flex with temperature changes or traffic loads. A stiff pavement is prone to various forms of cracking (thermal cracks in cold weather, fatigue cracks under repeated loads, and so on). New-generation binders, being harder to begin with, often have less “reserve” before they hit that brittle state. In essence, the window of time during which the pavement remains flexible and forgiving is reduced.
Several real-world indicators point to this issue. Some Departments of Transportation have noticed that even when using the correct grade of asphalt (say a PG 64-22, common for many U.S. states), the longevity can differ based on the source of that binder. One source of PG 64-22 may lead to pavements that crack after only a few years, whereas another source might last much longer before showing distress - even though both met the same specification initially. This variability often ties back to how the binder was produced and what's in it. Industry conferences and studies have raised alarms that “hard” binders today are contributing to premature pavement cracking, especially in colder climates or when using reclaimed asphalt mixes with already-aged binder. In response, researchers have developed additional tests to characterize binder brittleness (for example, the ΔTc parameter in asphalt binder testing, which helps detect low-temperature relaxation properties of an aged binder). The fact that such tests are needed underscores that traditional specifications sometimes don't capture this new brittleness issue.
Another impact is on pavement maintenance cycles. If a pavement is oxidizing faster, municipalities may find they need to apply rejuvenators, seal coats, or overlays sooner than expected to ward off serious cracking. The typical design life of an asphalt road (say 15-20 years before major rehabilitation) could shrink if inferior binder leads to crack networks (alligator cracking, block cracking) forming in 5-10 years. Oxidation and embrittlement can also manifest as raveling, where the binder can no longer hold the aggregate stones in place and the surface begins to erode. All of this means higher life-cycle costs: more frequent repairs, earlier need for resurfacing, and potentially more complaints from road users about potholes and roughness.
It's not all doom and gloom, however. Recognizing these challenges, the asphalt paving industry and government agencies have been adapting with improved specifications and materials. The late 1990s saw the introduction of the Superpave Performance Grade (PG) binder system, which was one move to ensure asphalt binders are selected based on climate and expected traffic, rather than just penetrometer or viscosity values. Superpave brought in tests that simulate aging (Rolling Thin Film Oven and Pressure Aging Vessel) so that suppliers must prove the binder will still perform after some level of oxidation. This shift has forced refineries and asphalt suppliers to pay more attention to the chemistry of their product. In fact, after Superpave specs became widespread, refiners began to view asphalt not just as a dump for leftovers but as a value-added product requiring controlled formulation. Some refineries invested in producing higher-quality paving grades (or they exited the market if they couldn't economically meet the new standards). Performance grading helped ensure, for example, that if the heavy oil was over-processed, the supplier would need to modify it (perhaps with a softer flux oil or a polymer) to still meet a PG XX-28 low-temperature requirement.
Still, even with these specs, the issue of long-term oxidative aging remains. Research is ongoing, and agencies are tweaking requirements (such as limits on how “stiff” a binder can get after extended aging, or requiring certain additives). It's a dynamic situation - as refining continues to evolve (and may evolve further if fuel demands drop in the future with electrification), asphalt technologists are continuously seeking ways to mitigate the negative impacts on pavements.
Strategies to Improve Asphalt Durability (Solutions)
Public works professionals are not powerless in the face of changing asphalt quality. Several strategies and innovations can help ensure pavements remain durable even if the base binder is less forgiving than before. Below are some key approaches to consider:
- Polymer-Modified Asphalt (PMA): One of the most common solutions is to modify the asphalt binder with polymers (such as SBS - styrene-butadiene-styrene, or crumb rubber from tires). Polymer-modified binders have improved elasticity and strain tolerance, which counteracts brittleness. They can significantly enhance a pavement's resistance to cracking (especially fatigue cracking and thermal cracking) by essentially “reinforcing” the binder with a rubbery network. Studies have shown that polymer-modified asphalts greatly improve a mix's ability to handle repeated bending and stretching without fracturing. Many highway departments now specify polymer-modified grades (like PG 76-22 or PG 70-28 with a “P” designation) for heavy traffic or cold regions. While PMA comes at a higher cost, it often pays off in longer service life and fewer repairs. For local agencies, using PMA on critical roads or at least for the surface layer can be a wise investment in durability.
Rejuvenators and Binder Additives: If the core problem is a lack of maltenes (oils) in the binder, the intuitive fix is to put some back in. Rejuvenators are additives - often proprietary blends of oils, waxes, or other chemicals - designed to restore flexibility to aged or over-processed asphalt. They are commonly used in recycled asphalt applications (to soften the old binder from reclaimed asphalt pavement, RAP), but can also be used for virgin mixes made with very hard binders. The inclusion of certain functional oils can make the asphalt binder more workable and ductile. For example, adding small percentages of plant-based oils, fatty acids, or even re-refined engine oil bottoms (REOB, though controversial) can replenish some of the lighter fractions that were missing. It's crucial, however, to dose rejuvenators correctly - too much can make the binder too soft or prone to rutting. Various state DOTs and researchers have field-tested rejuvenators both as spray-on surface treatments and as mix additives. When properly used, rejuvenators can extend pavement life by reducing cracking and delaying oxidation. In essence, they help the binder behave as if it were “younger” or less heavily refined. Public works officials might encounter rejuvenator products marketed for pavement preservation; understanding their role can help in selecting treatments for aged pavements. Always look for evidence (e.g. case studies or lab results) that a given additive truly improves long-term performance and doesn't just meet the spec on day one.
Performance-Based Specifications and Testing: As mentioned, the introduction of Superpave PG specifications was a leap forward in addressing climate-related performance. Going further, agencies are now embracing performance-based specifications for asphalt mixes as well, which complement binder specs. This includes approaches like Balanced Mix Design (BMD), where laboratory tests for both rutting and cracking performance are run on the asphalt mix itself (e.g., Hamburg Wheel Track test for rutting, and Indirect Tensile or Disc-Shaped Compact Tension tests for cracking). By doing so, even if a binder is on the stiffer side, the mix can be adjusted (with more binder content, different aggregates, or additives) to ensure it meets a cracking threshold. Performance tests essentially hold the producer accountable for the end result - a pavement that won't crack excessively - rather than only checking ingredient properties. Public works professionals can advocate for or implement these performance-based specs in contracts. For instance, rather than just specifying “PG 64-22 binder, Level 3 mix,” an agency might require that the mix achieve a minimum flexibility index or maximum creep stiffness after aging. This pushes contractors and suppliers to use whatever means necessary (softer binder, polymer mod, fibers, etc.) to get a good result. The Superpave system itself continues to be refined; new grading metrics like PG “plus” tests (e.g., a parameter for binder brittleness after extended aging) are being discussed in industry groups. All of this is geared toward ensuring that the asphalt that goes on the road is not only meeting a lab number, but actually performing well for years under real conditions.
- Innovative Surface Treatments (e.g. PressurePave®): Another angle to attack the problem is on the pavement preservation side. If the binder in the asphalt is aging faster, we can apply treatments to slow down the aging or to seal and reinforce the surface after cracks form. One novel example is PressurePave®, a proprietary process that has been gaining attention in pavement preservation circles. PressurePave is a hybrid treatment that pressure-injects a ductile stress absorbing mastic into the pavement's cracks while simultaneously placing a thin asphalt driving surface. In effect, it's sealing existing cracks from the inside out and covering the pavement with a fresh, durable driving surface in one go. The injected mastic is more flexible and crack-resistant than typical asphalt driving surface, which means that even if the pavement on top shows hairline cracks the mastic underneath can remain sealed under the surface. According to the developers, this method can extend the life of moderately distressed roads (PCI scores 40 - 70) by 12 - 15 years, delaying the need for a full mill-and-overlay. For public works departments, treatments like this can be a game-changer: they allow intervention at a later stage of distress and arrest deterioration before it becomes full-depth failures. The key takeaway is that by using preservation tactics - essentially giving the asphalt binder a “boost” or protection partway through its life - one can counteract some of the drawbacks of a less-than-ideal binder. It's much like applying lotion to dry, cracking skin; the sooner you do it, the longer you stave off a bigger problem.
Conclusion
Advancements in oil refining have undoubtedly benefited society by providing more fuel and cleaner-burning products, but as public works professionals, we must recognize the ripple effects on the materials we use. The asphalt binder that holds our roads together has become, in many cases, a more refined (and not necessarily better) material than it once was. Understanding this connection - that refinery processes upstream affect pavement performance downstream - empowers us to make smarter decisions. We can adjust our specifications, choose modified binders or additives, and implement proactive maintenance to ensure our roads remain durable.
Educating stakeholders about this issue is important: when a road cracks prematurely, the cause isn't just traffic or weather - it could be the invisible history of that asphalt binder. By staying informed about material quality and embracing modern solutions (like polymer modifiers, rejuvenators, performance testing, and innovative treatments), public works engineers and managers can mitigate the challenges of today's asphalt. With a combination of good science, updated practices, and a bit of ingenuity, we can continue to build and maintain roads that serve the public well, even in this era of cleaner fuels and, hopefully, cleaner, longer-lasting pavement surfaces.