Sustainability has become a central topic of focus across all sectors of the asphalt paving industry. Local governments and departments of transportation are considering how updated specifications can lead toward meeting broader net zero emissions goals. Producers and contractors are looking for different technologies that can help meet performance requirements while lowering their own carbon footprint and keeping operations cost effective. Researchers are hard at work assessing the roles of climate, bitumen quality, and additives in creating balanced mix designs that pass various performance tests.  

 

In short, sustainable asphalt paving has become more than a lofty goal; it’s a reality impacting paving across the globe. While bitumen has a poor reputation since it is sourced through oil refining, which taxes fossil fuel resources and contributes carbon emissions of its own, asphalt paving provides other opportunities for environmental considerations. Sustainable roadway surfaces are ultimately the product of a combination of responsible sourcing, environmentally friendly production, recycled asphalt use, and extended lifecycles.  

 

What is Sustainable Asphalt Paving? 

Understanding the often-obscure definition of sustainability in asphalt pavements can help the industry make tangible progress toward more environmentally friendly outcomes. Meaning varies across entities including National Highways in the UK, the United Nations, individual states across the U.S., and Austroads (the association of Australia and New Zealand transport agencies). To establish a baseline that encompasses the high-level concerns of most, reference the National Asphalt Pavement Association (NAPA) guide on the topic.  

 

Sustainable paving is that which serves a direct performance intent without degrading the environment. Further, project objectives should consider engineering, ecosystems, economics, and safety outcomes for all who are involved in, benefit from, or are impacted by roadway development or maintenance.  

 

Sustainable paving considers:  

  • Energy consumption 
  • Emissions output 
  • Waste reduction 
  • Local material use 
  • Additives and modifiers 
  • Runoff management 
  • Longevity and durability 
  • Safety and performance 
  • Heat absorption 
  • Permeability 

 

Asphalt Sustainability Examples 

Improving sustainability of asphalt roadways requires an overarching strategy that is agile enough to evolve as standards change and methods progress. The following are just a few examples of sustainable paving technologies.  

 

Reclaimed Asphalt Pavement (RAP) 

For decades, the use of RAP has led conversations around more environmentally friendly paving solutions. Aggregate materials are harvested from older, failing roadway surfaces and recycled through a robust process of milling, fractionating, and homogenizing so the material can be reused in new pavements. While the aggregate does not change over time, the binder in the original roadway material ages. Because of this, an effective asphalt rejuvenator is added to the RAP mix to restore the functional properties of the aged bitumen.  

 

In the U.S. alone, 89.2 million tons of RAP are used annually in new construction at an average rate of 21.1% in new asphalt mixes. Using RAP can help reduce waste, energy consumption, and the need for virgin aggregates and virgin bitumen in a mix. Incorporating a rejuvenator that is also sustainability sourced, like ReLIXER®, can further sustainability goals by using products that do not add to carbon emissions output. 

 

Warm Mix Asphalt (WMA) 

Asphalt is typically produced, transported, and compacted at high temperatures in order to ensure workability and facilitate compaction for more durable roadway surfaces. However, maintaining those temperatures requires energy consumption and subjects workers to uncomfortable conditions. Using WMA can help reduce temperatures between 30 to 120°F less than traditional hot mix asphalt applications. Lower temperatures may result in reduced greenhouse gas (GHG) and asphalt emissions Using 20-75% less energy to produce than hot mixes may also lead to lower costs. 

 

To achieve these lower temperatures without sacrificing the pavement compaction to desired specification, a warm mix additive is typically introduced to the mix. These additives, such as PHALANX®, do not change binder characteristics such as Penetration/Softening Point or PG Grade while supporting lower production and compaction temperatures.  

 

WMA is also compatible with other sustainable paving examples including reclaimed asphalt pavement. In fact, combining RAP and WMA can result in CO2eq reductions of nearly 25%. 

 

Sustainable Material Use 

Incorporating RAP into a mix is just one way to leverage sustainable materials in asphalt paving. Few asphalt mixes are developed solely on the basis of aggregate and binder. Instead, modifiers and additives are introduced to different mix designs in order to achieve specifications. Choosing additives that support, rather than inhibit, sustainability goals is an important consideration.  

 

For example, high-RAP mixes are dosed with a rejuvenator, but not all rejuvenators are produced in the same way. Asphalt rejuvenators span petroleum-based products, used cooking oils, and even re-refined engine oil bottoms (REOBs). The production of these products and the potential for chemical leeching into the surrounding environment can be environmentally adverse. In contrast, ReLIXER is formulated from a blend of bio-based oils sourced from crops that do not impact food sources. Independent testing has demonstrated ReLIXER’s global warming potential to be -1.451, supporting a lower carbon footprint. 

 

Extended Surface Life 

New roadway development is approaching all-time global highs through increased urbanization while existing infrastructure demand ongoing repair and maintenance. Sustainable roadway surfaces require more than environmentally friendly construction practices; they need to be able to stand the test of time. Developing more durable, high-performing surfaces that can resist factors such as rutting, cracking, and fatigue due to material degradation from traffic and weather conditions is critical for environment and economics.  

 

Choosing the right materials that balance upfront costs, aggregate and binder quality, and additive impact can lead to roadway surface designs that last. Mixes with up to 100% RAP dosed with ReLIXER have surpassed rutting resistance specifications. PGXpand®, a bitumen-friendly polymeric additive, has been shown to achieve not only outstanding rutting resistance but also excellent fatigue properties and weathering performance.  

 

 

At Sripath, we understand the unique challenges facing the asphalt and bitumen industries. Balancing sustainability requirements with performance specifications is a challenge facing producers and departments of transportation in nearly every geography. Our sustainably focused products are tried and tested the world over and supported by local experts who can help.  

 

For more information about Sripath’s sustainability efforts and product portfolio, contact info@sripath.com.  

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