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This is the Fall 2016 edition of the quarterly BINDER TECHNICIAN NEWS brought to you by the Asphalt Institute.

Ask Mike

Michael T. Beavin
Technical Training Coordinator
Asphalt Institute


Question: I have a question regarding the BBR bath fluid. I’d like to use a mixture of isopropyl alcohol and distilled water and after reading the specification, it meets the density requirement and is clear enough. Do you know of anyone using this or if there’s an official reason or opinion on using this from ASHTO or ASTM?

Mike Aurilio
QC & Product Development Coordinator
Yellowline Asphalt Products Ltd.


Answer: I hope you weren’t looking for an especially fascinating and thought-provoking answer. There are a few reasons alcohols are used for the BBR bath fluid.
1. Alcohol is particularly light compared to water. Previous versions of the AASHTO T-313 standard allowed the use of ethylene glycol for the bath fluid but it was so heavy that the lighter binder would float resulting in comical scenes of technicians trying to ‘catch’ the test beam in order to test it. Pure water has a specific gravity of one. All paving grade binders are heavier than water with specific gravities ranging from approximately 1.020 to 1.040.and will sink when submersed. This is good but…
2. Water freezes at BBR test temperatures. Imagine running the test in a block of ice.
3. Alcohols do not affect the properties of the binders other than the expected temperature-related stiffening.
4. Finally, alcohols remain clear within the range of BBR test temperatures. This is the most practical reason. You can’t conduct the test if you can’t see the test specimen.
 I do wonder why you are choosing an isopropyl alcohol/water mixture. It should work fine so long as you take care that the water to alcohol ratio doesn’t allow freezing. We use denatured alcohol. You can buy it by the gallon at any home improvement store inexpensively and it doesn’t require mixing. I hope this answers your question adequately and we are looking forward to seeing you again soon.

Submit your binder question to Mike Beavin for future newsletters.

Need an NBTC class or recertification? Here are our 2017 dates:

January 17-19, 2017
March 14-16, 2017
April 4-6, 2017
November 14-16, 2017


We look forward to seeing you in Lexington!


 
What Halloween taught me about G*/sinδ
    
Izzy, the neighbor kid, gave me a pack of gummy bears from her trick-or-treat bag. I thanked her, took them to work and loaded one in a DSR – obviously. Then I waited, rather smugly, for the test results that would confirm the central point behind the article you are presently reading. It didn’t tell me what I wanted to hear. In fact, it did the opposite of what I was expecting. Either that bear was a liar, resented being flattened to 1mm thick or I had more homework to do.

If you’ve operated a DSR more than a couple times, you know that the primary report parameter for high temperature tests in the M 320 system is G*/sinδ. You may not, however, have pondered its significance. So, let’s ponder. You’ve noticed that stiffer binders pass the 1.00 and 2.20 kPa tests at higher temperatures than softer ones so it seems that the parameter is all about stiffness. If we were only interested in G*, that would be correct. G* represents modulus and modulus represents stiffness. So, what is all that other stuff tacked onto the end? Why do we divide the stiffness by the sine of δ? Heck, what IS δ? That’s where it gets interesting – and confusing and requires some sweet references.

Chop the "/sinδ" off of G*/sinδ you are left with G* (modulus) which is a measure of how easy it is to deform or stretch something. To illustrate, let’s dig through that bag of trick-or-treat candy that Izzy amassed and shouldn’t be eating anyway. Jolly Ranchers and gummy bears will work fine. You’ll need something to drink too so pour yourself a cup of apple cider and, for no apparent reason, grab the honey out of the cupboard. Go ahead and squeeze the Jolly Rancher between your thumb and index finger and then do the same with a gummy bear. Then, pour a little cider and honey on the table. The differences should be obvious. It would take a heck of a lot more squeezing to squash the Jolly Rancher. The gummy bear was pretty soft. The cider and honey became larger puddles but they did it at different speeds.



If you were to measure the G* of both candies and both liquids in a DSR, you would certainly see that the Jolly Rancher has a higher modulus (stiffness) than the other three things. It’s just harder. Even a kid knows that. So, it stands to reason that if we lived in a world where we paved roads with sweet things, and we didn't want them to deform under traffic, Jolly Rancher roads might seem like the way to go. Besides, paving with apple cider or honey would just be silly.


Before we start paving with Jolly Ranchers, let’s look at some variables. It’s not all about how easy it is to squish something, it’s also about what happens after the squishing occurs. Lay the business end of a hammer on the Jolly Rancher for a minute and watch as nothing seems to happen. It just sits there. Sounds like good news if you were to drive on it, right? Now smack it good with the hammer and what do you get? Jolly Rancher dust. Given the abuse our roads take, is brittle a good thing? Maybe not.

Do the same with the gummy bear and what do you get? A slightly flatter bear at first but give it another minute and you will hardly know you whacked it at all. A gummy bear isn’t as stiff as a Jolly Rancher but it sure can remember what it’s supposed to look like. If you had used a much heavier hammer, however, and hit it much harder, that bear would still be sweet but wouldn’t look very bear-like anymore because you just rearranged its molecules. Some things can be awfully tenacious, but everything has a breaking point. Take a guess at what would happen if you took a hammer to the cider or honey. The cider would splash and the honey would splat. Either way, you’d have a sweet mess.
 
Very different responses, right? Yes, but both candies share a characteristic. They both resist failure or, in other words, they don’t like to give up (dissipate) their energy like apple cider and honey will. They like to store their energy and not flow. The Jolly Rancher resists changing shape (strain) when squeezed and the gummy bear recovers to its original shape after being squeezed. In other words, the end result is an object that looks the same after a force was applied as it did before unless the force was so great that the material fractured or sheared (dissipated its energy). The cider and honey also share a characteristic. They flow but at different rates. They fail.

 
Using the examples above, we can see that too brittle or too fluid is bad for a road and some recovery is good, which brings us to that "/sinδ" I promised to explain (deep breath). It might be good to throw in some asphalt binder references now, considering this is the Binder Technician Newsletter. We are good with G* and the concept of stiffness, right? A binder with a high stiffness is less likely to deform under traffic load. Now let’s look at δ or delta. Delta represents the phase angle which is simply a way to quantify elastic and/or viscous properties.

Elastic properties allow the binder to store (recover deformation or not deform at all) energy and viscous properties allow the binder to dissipate (flow and not recover) energy. Jolly Ranchers and gummy bears are more elastic, with phase angles closer to zero. Cider and honey are more viscous, with phase angles closer to ninety. If the phase angle falls somewhere between zero and ninety, it has viscoelastic properties and its stiffness is reported as a ‘complex’ modulus because it possesses both properties.

Be careful how you use the word viscous. Viscosity is a measure of a material’s resistance to flow. In phase angle language, "completely viscous’" means the stuff REALLY likes to flow and it can’t remember where it came from. In the rest of the world, viscous means sticky, thick or gummy. Same word, different meaning.

Likewise, if it isn’t budging or can unbudge itself, it is "completely elastic." I’ll put it in plain terms. At high temperatures, a binder with more of an elastic (stored energy) component is less susceptible to rutting than one with more of a viscous (dissipated energy) component. By dividing the G* by the sine of the phase angle we can factor the elastic component into the modulus. Do the math and you will see that as the phase angle decreases, the G*/sinδ increases. In this way, the valuable rut-resisting component of the binder is rewarded.

So, what did the flattened gummy bear say after being oscillated upon? Nothing, gummy bears can’t talk, but if they could, it would say “Gee, Mike, you just flattened me, tested me at a temperature I didn’t like and at a speed that was completely inappropriate for gummy bears. I quit.”  That’s gummy bear for “Accurate phase angle measurements depend on a lot more than meets the eye – temperature, speed, force, etc.”

 

TECH TIP

Getting krafty in your lab

What do you use to clean asphalt binder off of your lab counters? Citrus solvent? Mineral spirits? Or do you really throw caution to the wind and hose them off with toluene or trichloroethylene? (Seriously, if you are still doing this, please reread the MSDS/SDS. Yikes!)


Every solvent has associated risks, but what are you gonna do? That binder ain’t gonna clean itself! What do you use to wipe them with? Cloth or paper towels? And the most important question: How much satisfaction does the whole process give you? I’ll answer that one for you. Zero.

Solution? Cover your counters so the binder never goops them up to start with. How? Pick up a few rolls of brown kraft paper and cover your work surfaces with it.

Now the paper takes the abuse but when it gets dirty, leave those nasty solvents in the cabinet, toss it in the trash and replace it with fresh paper. We’ve done this for so many years it seems obvious to me but I’ve lost count of the number of folks that visit our lab and then make a bee-line to the store for a roll.


Did I mention that solvents are more expensive than paper?   
 

- Mike Beavin, Asphalt Institute Technical Training Coordinator
 

Technician Spotlight



Brian Waterbury
Amec Foster Wheeler Environment & Infrastructure
Bituminous Laboratory Manager

 
Brian has worked in the paving industry for 21 years. He currently oversees workflow in the lab where they perform a variety of tests for PG verification, PG classification, emulsion certification, RAP binder recovery and much more.

"The NBTC course helped fine tune and refine the experience I have gained working in our lab and helped me pay more attention to detail with daily testing," said Brian.

Learn more about this program at www.bindertechnician.com




The Asphalt Institute, in cooperation with the North East Transportation Training and Certification Program (NETTCP) and working with the AASHTO Materials Reference Lab (AMRL) and industry leaders, has developed one consistent, national PG binder technician certification. This map indicates the states that have USERS/PRODUCERS (in yellow), PRODUCERS (in green) and USERS (in brown) who have been nationally certified by the Asphalt Institute’s National Binder Technician Certification program.
 
Ultimately, the Asphalt Institute would like to see both certified users and producers in every state. There are now 38 states with users and/or producers who are nationally certified by the AI NBTC and the NETTCP programs. Click the map…
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