Rutting remains a threat to long-term asphalt pavement durability on a global scale. These depressions in the roadway surface that appear as grooves from wheel paths can occur due to repeated heavy traffic with, frequent start and stop, especially in climates with extreme high temperature.  

 

More than an inconvenience or imperfection, rutting can result in unsafe driving conditions, increased maintenance and repair costs, and shorter overall pavement life. In addition to these concerns, sustainability mandates for the materials in use and the expected longevity of the roadway pose a unique set of challenges.  

 

To build more durable, rutting resistant roadways, contractors and municipalities are exploring ways to leverage polymer modified bitumen (PMB) mixes and asphalt additives to meet performance specifications.  

 

What is Rutting in Asphalt Roadways and Pavements? 

Rutting is a permanent deformation in a paved surface typically caused by repeated loading and elevated temperatures. Rutting appears in the wheel paths of a roadway and can manifest within just a few months of construction if materials or design choices fail to meet specifications. Understanding the causes of rutting in order to prevent it from occurring can also save contractors and departments of transportation valuable time, funds, and carbon emissions.  

 

Several factors that can contribute to rutting include: 

  • Inadequate binder stiffness: Soft or improperly graded binders can deform under pressure. 
  • Poor aggregate binding: Weak structure in the aggregate skeleton can allow horizontal movement under traffic. 
  • Extreme temperatures: High temperatures can lower binder viscosity and making rutting more likely. 
  • Insufficient compaction: Poor density during construction can increase likelihood of rutting as the roadway compresses over time. 

 

Why Rutting on Roadways is a Problem 

Rutting does more than ruin a smooth-looking surface. Roadway rutting can affect drivers, infrastructure managers, and transportation systems. It can also reduce road network reliability while increasing the total cost of ownership. 

 

Most importantly, rutting can cause issues with regard to road user safety. From drivers and operators to passengers, anyone traveling a road with significant rutting can be at risk for an accident. The ruts can channel water during rain events and increase the risk of hydroplaning. In addition, deep ruts can destabilize steering and cause dangerous handling issues, especially for smaller vehicles. 

 

Rutting can also result in reduced ride quality. Driving experiences deteriorate as ruts deepen due to uneven surface travel and potential tire damage or vehicle alignment issues. This can cause an increase in complaints to municipalities about road quality, which can lead to demand for repairs.  

 

While filling or overlaying shallow ruts may temporarily mitigate the issue, rutting often requires more in-depth intervention such as resurfacing, milling, or full-depth patching. These repairs and replacements are also typically unplanned and unbudgeted. The result can be an unanticipated strain on financial and personnel resources since the roadway surface is failing well before its projected life expectancy. Maintenance projects can also cause inconveniences from lane closures and work zones that can disrupt traffic and add delays. 

 

Durability is an often-overlooked pillar of sustainability. However, a roadway that lasts longer without requiring frequent repairs or resurfacing can save critical environmental resources and help meet carbon emissions goals. PMB-enhanced pavements can help with this by reducing the frequency of costly, carbon-intensive repairs. 

 

  • Fewer work zones can reduce fuel burned by traffic backups and construction vehicles 
  • Lower material demand can reduce emissions, virgin material use, and quarry impacts 
  • Extended life cycles can increase the overall value per ton of asphalt 

 

How Common is Rutting in Roadway Pavements? 

Rutting remains one of the most prevalent forms of asphalt pavement distress globally. It’s especially common in high-volume corridors, urban intersections, and hot-weather regions. These environments share the conditions of traffic loading and environmental factors that can put constant stress on the roadway surface.  

 

According to the Federal Highway Administration (FHWA), rutting is among the top three surface distresses for roadways. In the U.S., over 30% of asphalt pavements exhibit rutting, with severe rutting (over 0.5 inches deep) affecting more than 6%. In India, where in some regions temperatures can regularly exceed 100 °F (38°C), rutting accounts for 19.82% of observed road deformations.  

 

As freight traffic increases and axle loads grow heavier, rutting is expected to become even more prevalent. The U.S. Bureau of Transportation Statistics projects a 40% increase in freight tonnage by 2050. Alongside rising global temperatures that can compound roadway performance in regions already exposed to high heat, rutting is not only common but increasingly prevalent.  

 

The Role of PMB Additives in Rutting Resistance 

Polymer modified bitumen is a binder enhanced with polymers to improve performance characteristics. PMBs are generally more common for use with roadways under high-stress and or exposed to high-temperature conditions. These polymers can interact with the base binder to create a more flexible, elastic, and temperature-resistant material. 

 

PMBs are specifically engineered to address the weaknesses of conventional binders when it comes to rutting. Standard paving-grade binders can soften under heat and lose its ability to recover from repeated loads, leading to permanent deformation in the wheel paths. PMBs, on the other hand, may maintain their structure better in hot climates and under heavy traffic. This makes PMB-based mixes an ideal choice for highways, intersections, loading zones, and other high-demand roadways. 

 

PMBs can offer significant performance and lifecycle cost benefits by reducing the frequency of rutting-related maintenance and improving overall pavement durability. Additional benefits of PMB mixes for rutting resistance include:  

  • Higher stiffness at elevated temperatures 
  • Enhanced binder-aggregate interaction 
  • Greater fatigue resistance 

 

Using PGXpand® to Enhance PMBs Against Rutting 

PMB additives vary greatly depending on the type and composition. Traditional elastomeric polymers, such as Styrene-Butadiene-Styrene (SBS), are designed to increase elasticity and provide adequate rutting resistance. However, they typically require high shear mixers, long mixing times, and high mix and paving temperatures, all of which can add to production timelines and energy consumption. Plastomeric polymers like ethylene vinyl acetate (EVA) provide good rutting resistance but may struggle to deliver desired fatigue properties. They also require high mix and paving temperatures along with extended mix times to produce the PMB.  

 

PGXpand® is a bitumen-friendly polymeric additive designed to deliver excellent high temperature performance, paving grades, and softening point while reducing mixing times and energy consumption. PGXpand is also highly dosage efficient compared to SBS and requires low shear mixing processes. Independent testing of a binder dosed with just 1.2% PGXpand demonstrated superior rutting resistance compared to the base binder and the base binder with 3.5% SBS. Additional tests have shown that binder dosed with 1.5% PGXpand can outperform crumb rubber PMB mix when evaluating viscosity, softening point, penetration, and rutting resistance.  

 

PGXpand can also: 

  • Improve the compatibility and dispersion of polymers within the asphalt binder, ensuring the roadway surface withstands repeated wheel loads. 
  • Enhance high temperature performance to improve PMB stiffness and structural integrity. 
  • Boost stiffness while retaining binder flexibility to resist rutting without sacrificing fatigue performance. 
  • Integrate seamlessly into existing plant operations and is easy to handle  

 

For more information about polymer modified bitumen and PGXpand, contact info@sripath.com.  

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