Sustainability in asphalt is a topic of increasing industry importance as more departments of transportation and contractors look to reduce their carbon emissions without compromising roadway performance. With a number of governments setting goals for net zero carbon emissions (such as the United Kingdom’s net zero efforts by 2050 and Australia’s aim to reduce emissions below 43% of 2005 levels by 2030), highway and transportation sectors are being asked do their part with sustainable paving development.  

These efforts take many different forms, from increasing the percentage of RAP used in balanced mix design to using additives that allow for lower temperatures and, subsequently, lower fuel consumption. Responsible material and third-party product sourcing can also directly impact emissions considering the amount of recycled material available and cradle-to-gate estimates for how materials and additives impact the overall carbon footprint.  

Every percentage point counts when it comes to reducing carbon emissions. The National Asphalt Pavement Association (NAPA) found that increasing reclaimed asphalt pavement (RAP) usage by one percent can reduce emissions by 0.14 MMT CO2e, enough to account for annual emissions of 30,000 passenger cars. Additional research has shown that warm mix asphalt (WMA) technology can lower greenhouse gas emissions by 20-35%.   

Here, we’re taking a look at sustainability in asphalt and what the paving supply chain can do to meet environmental goals while continuing to adhere to performance metrics.  

Despite being sourced from non-renewable resources via crude oils, asphalt is a sustainable material. Asphalt used in roadway paving or roofing applications can be 100% recycled, and asphalt is the most recycled material in the United States. Studies have shown that 94% of RAP is used in new roadway construction, helping to reduce the need for virgin materials and keeping millions of cubic years of material out of landfills.  

Because asphalt can be recycled, the material also helps reduce the energy consumption needed for roadway production. This is achieved through several means including localized material sourcing, which cuts down on transportation fuel, and the ability to reduce the need for virgin bitumen, which saves on natural resources, and carbon sequestration opportunities, which refers to carbon stored in the asphalt rather than released into the environment.  

Increasing the amount of RAP in a mix can eliminate the need for large amounts of virgin aggregate and bitumen. To do this, an effective rejuvenator is needed to restore the functional characteristics of the aged binder and recondition the material for satisfactory roadway performance.  

 

Using environmentally friendly products that decrease energy consumption can also improve sustainability of asphalt. This includes recycling agents made with bio-based oils rather than petrochemicals and warm mix additives that can help lower production and compaction temperatures.  

 

Replacing worn and underperforming roadways with smoother, more durable surfaces is also a sustainable measure. Improved surfaces can increase vehicle fuel efficiency, with a 2% increase in fuel economy reducing vehicle emissions by 30 million metric tons.  

Asphalt is a proven construction material for long–lasting roadways delivering superior ride characteristics. Asphalt can be recycled and reincorporated into a new roadway when dosed with an effective rejuvenator to restore its functional characteristics. The material is also more porous than other substrates, such as concrete, allowing better water runoff management. Innovations in production and compaction technologies, such as warm mix techniques, allow for lower temperatures during preparation and construction, further lowering fuel consumption and carbon emissions. Asphalt roadways also contribute to noise reduction through sound absorption and surface textures that dampen noise pollution.  

Asphalt production can be sustainable when plants take certain measures to reduce their carbon footprint. Fuel combustion is the biggest cause of carbon emissions at asphalt plants, which is required to heat materials in order to reduce moisture content and properly homogenize mixes. By preparing and storing aggregates and RAP properly, plants can limit exposure to water and reduce the fuel and time needed to dry materials before adding them to a mix. Using locally sourced materials and reusing RAP from prior projects can also reduce carbon emissions produced during material transportation to the plant. Increasingly, plants are improving their equipment to decrease electricity consumption including more efficient fans and variable frequency drives for motors and pumps. 

Asphalt roadways can impact global warming, but sustainability in asphalt production is becoming more prominent through more efficient manufacturing and increased use of recycled materials. While roadway surfaces are vital infrastructure, they do absorb heat from the sun and emit it as ambient temperatures cool creating what are known as urban heat islands, or areas of more concentrated heat typically found in cities.  

Asphalt can be 100% recycled, making it a green technology. Ninety-five percent of reclaimed asphalt pavement, or RAP, was recycled into new mixes in 2021. Recycled asphalt can also meet the same performance requirements as roadways made with virgin aggregate and binder when coupled with an effective rejuvenator or recycling agent. Asphalt recycling notably reduces fuel usage and the need for virgin materials in a mix, helping reduce carbon emissions by 20% compared to non-recycled mixes.  

 

Asphalt recycling includes milling the existing roadway to collect RAP. The material is then taken to a plant where it is screened to remove foreign items. The resulting larger pieces of aggregate are crushed and then fractionated, sorting the material based on particle sizes from fine to coarse. When creating a mix, the plant operator will homogenize the aggregate to ensure consistency and quality of the raw material before adding it to any virgin aggregate or binder and an additive recycling agent to produce a balanced mix design.  

One of the most recycled materials in asphalt mixes is asphalt itself in the form of reclaimed asphalt pavement (RAP). This is material removed from old roadway surfaces and then processed to screen, crush, and fractionate the material that can be reused in an asphalt mix. Importantly, an effective asphalt rejuvenator may be required to incorporate higher amounts of RAP into a mix to help restore the functional characteristics of the aged binder. Other materials that may be incorporated into an asphalt mix include crumb rubber and recycled plastics.  

While the overall carbon footprint, or greenhouse gas emissions (GHG), figures are difficult to estimate due to variances in everything from terminal operations to selected crude oil slates and production processes, efforts are underway across the industry to be increasingly sustainable. This includes a closer look at how materials, transportation, plant operations, and on-site construction methods contribute to GHG.  

Net zero emissions goals are an essential component for determining environmental impacts for the asphalt industry’s sustainability efforts. A net zero emissions goal indicates that the amount of greenhouse gases (GHG) produced by a particular activity are counterbalanced by the GHG removed from the air during the project.  

 

Over 140 countries have set net zero emissions targets, accounting for 88% of emissions produced worldwide. To achieve these goals, departments of transportation and related industry agencies are exploring pathways to lower their carbon footprint through asphalt paving. This includes upgrading to more energy efficient equipment and transportation, using lower carbon fuel sources, lowering production and compaction temperatures, increasing the percentage of RAP used in mixes, and reducing waste production.  

Sustainability in asphalt roadway construction can help the environment by creating higher performing and more durable surfaces. Roadways resistant to fatigue, cracking, and rutting will last longer, reducing the need for resurfacing or maintenance projects that require additional energy consumption, fuel, and natural resources. Notably, high-RAP mixes can perform equally well compared to no-RAP mixes used in roadway development when dosed with an effective rejuvenator that restores the functional characteristics of the aged binder. This helps to create roads that are not only sustainably sourced but also able to meet performance specifications for enduring surfaces that require fewer emissions producing repairs. 

Additives designed to enhance asphalt mix performance by restoring functional properties can help support sustainability in asphalt. For example, using an effective asphalt rejuvenator or recycling agent can improve the functional characteristics of aged bitumen and enable engineers to incorporate higher amounts of reclaimed asphalt pavement (RAP) into their mixes. Other additives, such as warm mix additives (WMAs), can help lower both production and compaction temperatures, reducing the need for energy consumption.  

The increased use of high-RAP mixes through the use of an effective rejuvenator has risen as one of the more prominent approaches to promoting sustainability in asphalt. Incorporating a warm mix additive to leverage warm mix asphalt technologies during production and compaction of asphalt mixes can also help reduce energy consumption as well as fumes and odors on the job site.  

Balanced mix design (BMD) is the method of developing an asphalt mix in which roadway specifications are addressed through performance testing. This can enable plants to incorporate higher amounts of reclaimed asphalt pavement (RAP) and additives that can impact performance outcomes. BMD not only helps address performance specifications but also helps engineers formulate more cost effective and sustainable mixes that will last for the long term and require fewer repairs during the lifetime of the roadway surface. 

Warm mix asphalt requires significantly less energy to produce than traditional hot mixes because the temperature requirements for production and compaction are lower. In turn, this can require much less energy consumption and lower carbon emissions and resource depletion.  

While government regulations will vary by country and, in many cases, by specifications mandated on a more localized level, current trends are showing government support for sustainability in asphalt. More governments are requiring Environmental Product Declarations that demonstrate a product’s environmental impact to guide decision making. Some jurisdictions or departments of transportation are including requirements for the inclusion of minimum amounts of reclaimed asphalt pavement (RAP) in mix design for projects.  

A lifecycle analysis can help evaluate energy consumption and greenhouse gas emissions to target sustainability in asphalt production. These measures often include an assessment of the energy required at different stages of the roadway development process from sourcing to construction. Areas explored encompass fuel type and volume consumed during production, materials transportation to and from a plant, and compaction.  

 

Adopting more sustainable practices, such as warm mix asphalt (WMA) technologies, can help plants reduce their energy consumption. WMA can also reduce temperatures required for transportation to the job site and compaction on the roadway surface. Plant management of raw materials, such as reducing aggregate moisture content by just 1%, can reduce energy consumption by 14%. 

 

Through careful balanced mix design and planning, a longer lasting roadway surface can reduce the need for ongoing repairs and maintenance, helping reduce net carbon emissions over the useful life of the road. 

Environmental Product Declarations, or EPDs, are formal reports typically produced by an independent third party that offer insights into a product’s environmental impact after conducting a lifecycle analysis. These documents provide objective insights into how a material’s cradle-to-gate process affects greenhouse gas emissions (GHG) as compared to international standards. With consistent product categories and rules, EPDs make it easier to assess the differences between different products regarding their environmental impact, where those EPDs are made available.  

 

EPDs are important for helping stakeholders make informed decisions about the products they are selecting for incorporation into their asphalt mixes. Those agencies and governments with carbon emissions goals must consider the entire supply chain impacting their sustainability in asphalt measures and how individual products contribute to those objectives.  

 

With an increasing emphasis on sustainability, more asphalt paving contractors and third-party producers of additives are being asked to provide EPDs. However, not all organizations are transparent regarding their EPDs or the research findings.  

Sustainability in Asphalt and Sripath® 

Since its inception, sustainability in asphalt has been at the forefront of Sripath’s mission. In providing effective additive solutions for the paving and roofing industries, Sripath designs innovative products that address both performance and environmental concerns.  

 

Sripath products have been demonstrated to help contractors and plants reduce carbon emissions, conserve energy, and minimize waste. This is achieved through responsible sourcing and sustainable production of products that enable higher usage of recycled materials, lower production and compaction temperatures, and extended pavement lifecycles through achievable performance metrics in balanced mix design.  

 

Sripath’s Environmental Product Declarations are publicly available online, further demonstrating a commitment to sustainability and transparency.