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A feature article from APWA-MN Gold sponsor Asphalt Materials, Inc.

Every pavement preservation decision comes down to one question: will this treatment help the road perform better and last longer? If you are considering using a topical (“spray-on”) asphalt rejuvenator to mitigate the effects of asphalt binder aging on roads in your network, learn why rheological testing is the most objective and practical framework for evaluating its performance.

Asphalt Binder Isn’t a Solid or a Liquid—It’s Both
Most construction materials can be reliably classified as either solid or liquid within their standard service environment. Steel, for example, behaves as a predictable elastic solid, deforming under load and fully recovering its shape once the load is removed. 

Asphalt binder, however, does not behave so simply; asphalt behaves solid-like at low temperatures, but at higher temperatures exhibits properties of a viscous liquid, softening and deforming if loads are sustained for long periods. Critically, the deformation response of asphalt is dependent not just on the magnitude of load and temperature, but also on time. Because of this, asphalt is best characterized as a viscoelastic material, and it is the key to understanding pavement performance. 

The viscoelastic and temperature-sensitive nature of asphalt is a result of its composition. Asphalt binder is a complex hydrocarbon material — composed broadly of waxy and oily molecules that can be loosely assigned to four chemical categories: saturates, aromatics, resins, and asphaltenes (often abbreviated as “SARA” fractions). SARA fractionation reduces a highly complex, continuous molecular spectrum into just four fractions, potentially masking or confounding critical differences in molecular size, polarity, and functionality that strongly influence rheology and, hence, performance.

Don’t Measure What Asphalt Is—Measure How It Performs
Rheology is the study of how materials deform and flow under applied forces. For asphalt, rheology describes how the binder responds to stress, strain and temperature changes over time — factors that directly determine pavement performance. For this reason, rheology is correlated to pavement performance more reliably than chemical composition, and is the predominant framework used in the asphalt industry to measure asphalt binder properties. Will a road rut under heavy traffic? Will it crack in winter? How will it age over years of exposure? Rheological properties provide the answers. 

Rheology is already embedded in everyday engineering specifications. For example, the asphalt industry’s Performance Grade (PG) specification system is built on rheological measurements, not chemical composition. The PG specification framework classifies asphalt binders by performance across temperature ranges and aging conditions, linking material behavior directly to real-world conditions.

Rheology provides direct clarity for the most practical question “how will my asphalt binder actually behave under my expected traffic loads when exposed to my region’s weather environment?” something that chemistry alone cannot explain.  

Performance Matters, Rheology Measures It
The objective of asphalt binder rejuvenation is not merely to modify chemistry — it is to restore functional and mechanical performance in aged pavements. The key question is not whether a binder’s composition has changed, but whether the rejuvenator improves or restores the performance of the asphalt binder. 

Rheology provides the most direct way to answer that question by allowing practitioners to measure whether rejuvenated binders:

• Are resistant to traffic and climate induced distress across the entire service temperature range of the pavement 
• Resist or mitigate the effects of oxidative and UV aging of asphalt 
• Maintain durability over time

For agencies, this makes rheology the most reliable framework for:

• Specifying materials
• Evaluating supplier compliance
• Assessing field performance
• Managing long-term asset risk

Bottom Line for Agency Decision-Makers
For engineers responsible for balancing performance, cost, and sustainability across large pavement networks, success relies on selecting treatments that deliver long-term results. Asphalt rejuvenators can play a role in achieving those outcomes, so long as their impact on pavement performance is accurately measured and understood.

Rheology provides a direct, measurable framework to evaluate this performance. By focusing on rheological properties of rejuvenated binders, agencies can confirm whether desired properties have been restored. This performance-based insight enables more informed treatment selections and builds confidence that the chosen strategies deliver long-term pavement outcomes.

Ready to move from analysis to action? Jim Romanik is available to talk through pavement preservation strategies, asphalt rejuvenator performance or testing methods jromanik@asphalt-materials.com 651-274-5072