Asphalt Binder Testing: Anti-Aging Additives v. Asphalt Rejuvenators

Through balanced mix design, as we analyze our asphalt performance testing results, the goal is to predict future pavement performance.  We want to continue to find innovative ways to enhance asphalt pavement performance and extend its lifespan.  In Florida, cracked asphalt is the number one culprit of pavement deficiencies, so a great deal of focus is placed on asphalt binders and reclaimed asphalt pavement (RAP).  This sparked a rather philosophical conversation about asphalt binders, and we decided to propose our question on LinkedIn.

asphalt binder testing dynamic shear rheometer

Some of us at ATS were having a rather philosophical conversation the other day about asphalt binders, and we decided to propose our question on LinkedIn.

What’s better?  An anti-aging additive to prevent binder from ever aging (or to slow aging) OR a rejuvenator to continuously bring the recycled binder back to life?

We had a few great responses, continue reading:

“…Slowing the rate of aging new asphalt mixtures is of vital importance to our infrastructure.  The asphalt glue that is selected to bind rocks together to make a pavement is highly susceptible to oxidative age-hardening.  This is especially true for open-graded friction course (OGFC) pavements, which have higher air void content, and thus higher oxidative aging rates and shorter expected life as a result.  Using an anti-aging additive should be the immediate point of attack against OGFC mixture aging, which rarely incorporates RAP/rejuvenation. 

RAP is a waste product.  Therefore, RAP is used in scenarios where it causes the least damage to a new pavement, i.e. lower pavement layers and small percentages in layers nearer to the surface.  When RAP is properly restored to a higher performance level prior to reuse, the life cycle cost of the pavement containing RAP will be greatly improved.  Not only will the life cycle cost be improved but also the initial cost of the mix, if the plant can accommodate a higher RAP percentage.”  

– Grover Allen, Ph.D., P.E., Technical Director, Blacklidge Emulsions

After reading this response, ATS Pavement Materials Engineer, Tanya Nash, proposed this question:

“…Can you add these properties to rejuvenated RAP?  Once you rejuvenate the RAP binder it will still age as quick or quicker, as some believe, as a virgin binder.  With the recycled binder replacement going higher, is there a way to rejuvenate and delay the aging of this recycled binder all at once?”

Grover responded, “The anti-aging additive will make any asphalt more resistant to aging, including asphalts containing RAP.  The improvement will be relative to the asphalt, and the starting chemistry can potentially influence the extent of improvement yielded from the additive chemistry.”

Another conversation was introduced by Mohamed Elkashef, Postdoctoral Research Associate from UC Davis Pavement Research Center.  He also commented on the rejuvenation of RAP:

Reclaimed Asphalt Pavement (RAP)

“Rejuvenation of RAP can work to a certain extent.  When RAP is too stiff (excessively aged), higher dosage of rejuvenator is needed to restore the properties of the RAP leading to potential rutting problems.  Rejuvenation of RAP also doesn’t ensure that all the RAP binder becomes available (i.e. blends with virgin binder).”

Tanya commented on Mohamed’s thoughts: “I agree.  The more RAP, the higher that dosage of rejuvenator.  But there has been work done with 100% RAP and rejuvenator.  Is there somehow a combination of all these things – “anti-aging,” rejuvenator, plus anti-strip and warm mix/compaction aid, etc – that can be found in a single additive or are we asking too much in return from one product?”

In conclusion the contributors to this conversation seem to follow the same train of thought.  It’s ideal to attack the aging process from the beginning; using an anti-aging additive with the virgin binder.  However, it’s important to revitalize RAP binder when using RAP in the mix.  Tanya’s final question opens the door to innovators in our industry – who will develop an all-inclusive additive that includes a rejuvenator, anti-aging technology, anti-strip and compaction aid to enhance performance and elongate asphalt life?