The Future of Rubber Modified Asphalts

By: Tom Rosenmayer

Rubber modified asphalts (RMA) have been around for decades and offer excellent performance with significant environmental and cost benefits. Yet despite extensive real-world experience, RMA still constitutes less than 20% of modified asphalts, with much of that concentrated into a few states in America and a few minor applications in Europe.  We see two primary drivers for this:  limited application field and processability.

Decisions to limit the application field. Conservative transportation agencies commonly limit the pavement applications in which RMA can be used.  This limitation has unintended consequences throughout the supply chain:  For terminal blenders and contractors, life is much simpler with Polymer Modified Asphalts (PMA), rather than having to run both RMA and PMA.  The limited application scope also undermines the cost-savings potential with RMA, preventing RMA from achieving large scale with its associated cost benefits. Cost fluctuations due to petrochemical pricing (the inputs for SBS polymer are oil based) can be avoided by using “local” rubber powders also impacting product choice, further complicating the business for DOTs, blenders and contractors.

This may be changing, however.  Some states, such as Florida, Louisiana, and Tennessee have recently approved RMA grades such as FDOT’s 76-22 ARB for all 76-22 modified asphalt applications.  All qualified FDOT 76-22 ARB binders are hybrid binders, combining at least 7% rubber content with some amount of SBS type polymer.  These hybrids enable RMA binders to meet challenging MSCR elasticity requirements and “pave” the way for broadening the application scope.  We expect this trend to continue with growing confidence in the latest hybrid binders in more and more states.

Challenges remain on the processability front.  On one hand, RMA offers significantly more processing flexibility that PMA doesn’t have: It can be terminal blended, plant blended, or dry mixed in either powder or pellet form, and doesn’t require milling.  On the other hand, challenges with viscosity and stability sometimes appear, and preparation of hybrid systems can get complicated.

Lehigh is working hard to address these challenges and grow the application base for RMA.  Now supported by Michelin, Lehigh will continue to invest in the development of new sustainable modified asphalt technologies that meet or exceed the performance and processability of PMA for pavement applications. 

Michelin’s purpose states: “Because we believe that mobility is essential for human development, we are innovating passionately to make it safer, more efficient and more environmentally friendly. Our priority and firm commitment is to offer our customers uncompromising quality.  Because we believe that all of us deserve personal fulfillment, we want to enable everyone to do his or her best, and to make our differences a valuable asset.  Proud of our values of respect for customers, people, shareholders, the environment and facts, we are all sharing the adventure of better mobility for everyone.”

Michelin’s equation for sustainable mobility now includes Lehigh Technologies and rubber modified asphalt – a more sustainable option. We look forward to the growth and innovation that can result from this unique combination.  Won’t you join us?