Insights
Our experts share their thoughts on asphalt sustainability, innovation, safety and creating a culture of care.
Our experts share their thoughts on asphalt sustainability, innovation, safety and creating a culture of care.
Good Binders Make RAP and RAS Better
As more DOT specifications call for increased percentages of recycled materials in asphalt hot mix, many still need to be convinced about the performance of pavements paved with RAP and/or RAS. Additionally, there’s confusion over the environmental and financial impact of using recycled materials. These are all valid concerns.
However, using RAP and RAS alone is not the answer. We’ll explore how you CAN achieve better performance, sustainability and cost savings with RAP/RAS hot mixes using a performance grade binder.
Performance
A study by the University of Texas, El Paso (UTEP) evaluated mix designs, design processes and guidelines to identify weaknesses and strengths of balanced mix designs involving RAP, RAS and other additives. According to Soheil Nazarian, Ph.D. — a Civil Engineering Professor at UTEP and the lead researcher on this project — adding more binder enables a more flexible mix that doesn’t crack as easily.
This report by NAPA echoes Dr. Nazarian’s sentiment, stating that “high RAP/RAS mixtures can be designed to have better performance than virgin mixtures when a proper mix design approach (such as the balanced mix design method) is employed.”
We’ve seen many real-world examples in which roads paved with RAP and/or RAS perform the same, if not better, than standard-grade asphalt when a PG binder is added to the mix.
Sustainability
The environmental impact of upcycling pavements and shingles is felt both upstream and downstream in the asphalt supply chain. Using more recycled materials in mix designs not only diverts waste from landfills (up to 34% of landfill space, according to the NAPA report) but also reduces the need to source virgin materials — enabling a pavement lifecycle that is truly regenerative.
Additionally, that same report claims that RAP and RAS reduce energy by up to 15% — which is key for companies looking to lower their carbon footprint and adhere to EPDs.
At the same time, by engineering roads that last longer, we are naturally reducing the energy and waste materials required to maintain pavements.
Cost Savings
Increased performance and sustainability result in significant cost savings. According to NAPA, the savings from higher binder replacement significantly outweigh the cost of any extra testing that may be required. The total amount of asphalt and aggregate available on an annual basis can result in $5.1 billion in savings, with 70% of that savings embodied in the binder alone.
SigmaBond Checks All the Boxes
Using our SigmaBond modifier as a binder ups the ante for all the key benefits listed here. Because SigmaBond contains completely digested tire rubber, you can pack even more recycled materials into an asphalt hotmix. It’s the only terminal blend PG-TR and ARHM that routinely uses more than 15% RAP. SigmaBond also releases performance-enhancing qualities, such as resistance to cracking and fatigue, low-temperature improvement and reduced discoloration.
An independent study by the University of Nevada, Reno, correlated this performance improvement with a 10% to 25% reduction in construction cost per lane-kilometer when compared to conventional asphalt pavement. Learn about the science behind SigmaBond here.
We look forward to more studies and discussions around sustainable pavements and hope the asphalt industry continues on the path to reducing waste and building roads that last.