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This is the Spring 2019 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: Why is the equation for PAV DSR different than the equations for original and RTFO DSR (G*sin δ vs G*/sin δ)?
- Kenzie Adams, Coastal Energy Corporation

 
Answer: Ah, Kenzie, you’ve gone and asked a short question with a potentially “Gone With the Wind”-length answer. Great question, though. The long answer would require more space than we have here, so I’ll give you the plot summary. For the director’s cut, attend the Rheobit course here at the Asphalt Institute in October. The following scene sums up three distresses that are addressed in the PG system. The equations you reference address two of them.

The day was sultry. Even with her windows and doors swung wide, Tara could not provide the comfort to which her residents were accustomed. The shade of her verandas and grand hall beckoned but were empty in their promise of relief from temperatures not seen in a generation.

“Fiddle-dee-dee!” Scarlett loudly protested as she jerked her hand away from the doorknob “The candles have wilted, the doorknob is on fire and now the lane has permanent deformation! Whatever happened to civilized temperatures where my only concern was a little fatigue or thermal cracking now and then?”

Permanent deformation (rutting), fatigue cracking and thermal cracking – she may not have known it, but Scarlett was onto something.

We want our roads to withstand extreme high and low temperatures without rutting or thermal cracking and we want our roads to withstand years of service without fatiguing. The equations you reference are designed to combine two elements- stiffness and phase angle- in such a way as to account for the different properties we need at different temperature ranges. So, let’s dig into those equations.

G*/sinδ and G*sinδ look so similar that many technicians don’t notice the difference. But the way the equations handle the contribution of the phase angle is very different. First, the similarities. Both equations include G* and δ but what are they?

G*-modulus-stiffness- We intuitively know the concept of stiffness. A child knows that a tootsie roll is stiffer than a ripe banana. Stiffness is simply a measurement of how easy it is to deform something. G* is determined by calculating stress (force divided by cross-sectional area) and strain (deformation divided by elongation or original position) and then dividing stress by strain. In asphalt binders, modulus decreases as temperature increases so, without some ability to recover deformation, we would expect rutting at high temperatures.

δ-phase angle- An indication of the viscous and elastic properties of an asphalt binder reported in degrees from zero (elastic) to ninety (viscous). A zero degree phase angle indicates complete recovery after deformation and a ninety-degree phase angle indicates no recovery. Any phase angle from one to eighty-nine indicates viscoelastic behavior. Asphalt binders are viscoelastic within service temperatures but sometimes the proportion of the viscous and elastic properties does not suit the needs of the pavement

The amount of permanent deformation a pavement experiences doesn’t just depend on its stiffness. If stiffness was the only consideration, we could just stick with the penetration test. It also depends on its ability to recover deformation when it occurs. Likewise, the tendency to fatigue crack doesn’t just depend on one property, so we need to combine them.     

You may (or may not) remember from school that the sine of ninety is one. Divide anything by one and you get the same result, right? Right. As the phase angle (δ) decreases, so does the sine of δ. Divide a number by a smaller number and you get a higher number. The criteria for the high-temperature DSR tests are minimum values, so dividing G* by the sine of a lower phase angle shows the benefit of the elastic component and gives a higher result. We want more elastic (recovery) properties at high temperatures because remember as temperatures go up, a binder’s stiffness goes down.

At intermediate temperatures, research has shown that binders with higher viscosity (higher G* and higher phase angle) are more likely to exhibit fatigue cracking. So, change the equation a bit and multiply the G* by the sine of a lower phase angle and you get a lower value. The intermediate temperature criteria for DSR is a maximum value, so a lower phase angle is beneficial here too.

Whew! You hanging in there? Thank you if you are…and this was supposed to be the plot summary! I could have just cut to the chase and told you that the equations are different to account for the impact of the stiffness AND phase angle on pavement properties according to temperature and traffic load… but I didn’t, did I?   
 


Dissension can lead to change

By Mike Beavin

“We should be eternally vigilant against attempts to check the expression of opinions that we loathe and believe to be fraught with death.” - Oliver Wendell Holmes
 

The legendary Supreme Court Justice Oliver Wendell Holmes tells us that the expression of dissent must be preserved or we forfeit our freedom. He also recognized that even the most hallowed documents, including the constitution, were written by mortals and, as such, were not above scrutiny.

Holmes was not advocating lawlessness but the freedom to affect change through speaking out against ideas with which we disagree. If you are a binder technician, there are documents you should be familiar with and abide by. The ASTM and AASHTO standards are essentially laws. You must adhere to them regardless of your opinion of all or parts of them. I’m not insinuating that the published standards carry the same weight as the U.S. Constitution by any means, but the idea is the same. Whether it’s the law of the land or the law of the lab, the documents are binding….unless……unless you work to change the cause of your dissent.

In every Asphalt Institute course, we stress the importance of strictly following the published standards. We remind our students that going rogue and ‘fixing’ a part of a standard we disagree with doesn’t fix anything. It only entrenches a practice that may be contrary to the ‘fix’ by another technician in another facility. In other words, regardless of whether or not you agree with a subsection in one of the standards, you must abide by it or you become part of the problem of testing variability. If you think your opinion is shared by several other technicians, work to fix the issue the right way: by attending meetings and participating in the ASTM and AASHTO processes.

Do I dissent on some issues in the published standards? The answer is YES!

Here are a couple examples:

ASTM D92- Flash and Fire Points by Cleveland Open Cup Tester

Section 11.1.13  When the apparatus has cooled down to a safe handling temperature, less than 60 Celsius (140 Fahrenheit), remove the test cup and clean the test cup and apparatus as recommended by the manufacturer.

This requirement is impractical for many reasons. A typical, properly conducted COC flash test following ASTM D92 takes approximately 30 minutes. We followed the standard as written and recorded a flash point of 314 Celsius. Then, we immediately turned off the apparatus. It took the sample 55 minutes to cool to the ‘safe handling’ temperature. It took another 15 minutes to reheat the cup to a temperature considered unsafe in order to empty it. Section 11.1.13 more than triples the time needed to run the test. Dissent!  

AASHTO T 316- Rotational Viscosity

What to do if your rotational viscosity sample and chamber cools too much to allow you to ‘Gently lower the spindle into the asphalt binder…’? Is it permissible to reheat the binder in the viscometer during part of the 30 minute preheat period? If not, how do we handle this? Storing the sample in an oven while waiting for a free RV would be much more damaging to the sample than reheating from a cold state. The standard, as written, does not allow us to cool and store the sample in the chamber, which if properly covered is the same as a sample tin, while awaiting testing. Dissent!

I’ve been grousing about some of the same issues for years. Now I’ve written an article asking binder technicians to adhere to the standards regardless of opinion unless they speak up and get them changed. Looks like I need to do something that many of us ASTM members loathe and believe to be fraught with death: volunteer to help fix the issues the right way.  



TECH TIP

Absolutely simple



The glass cleaning oven – life in the binder lab before it was a dark and solvent-filled place with technicians fearful of dirtying a beaker, knowing of the labor, fumes and nitrile gloves needed to make it clean again.

Now? No worries. In go sticky, asphalt coated beakers, viscosity tubes and RTFO bottles and out come shiny, nearly spotless glassware ready to dust off and use. The dark days of cleaning with solvents are gone…right? Not so fast. If you’ve noticed a thin haze forming in the capillary of some of your absolute viscosity tubes after multiple cleanings in the GCO, you’ve probably also noticed that it’s very difficult and sometimes impossible to remove. This is especially true in the smaller capillary tubes. If the capillary isn’t perfectly clean, the friction caused by the film can change the timing of the test and increase variability.

What to do? Unfortunately, the GCO is our friend for beakers, RTFO bottles and many other lab glassware but not for viscosity tubes. Solvent may be the only way to go. But if we have to go there, let’s make it easy and safer.

Clamp the tube upside down over a waste container and place the apparatus in a hot oven for about 15 minutes. Move from the oven to a fume hood, flip the tube upright and immediately fill the tube with a miscible solvent of your choice (citrus works well). Let soak for about 5 minutes and suck the solvent and dissolved binder into a vacuum flask. Repeat as necessary and finish with a rinse of alcohol or acetone.

You’ll need:
• Fume hood
• Vacuum pump
• Vacuum flask               
• Hose
• Cork
• Glass tubing
• Ring stand
Two-prong clamp
• Waste container
   
- Mike Beavin, Asphalt Institute Technical Training Coordinator

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 45 states with users and/or producers who are nationally certified by the AI NBTC and the NETTCP programs. 
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