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This is the Fall 2018 edition of the quarterly BINDER TECHNICIAN NEWS brought to you by the Asphalt Institute.


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A binder's purpose

By Mike Anderson, P.E. 

I have not seen the movie “A Dog’s Purpose” which was released in 2017. When I saw the trailer it just screamed at me “Come. Spend a bunch of money to watch this tear-jerker with your spouse and salve your sorrow with a large tub of buttered, salted carbs.” Nope. Not for me. Even if it’s a decent family movie.

Anyway, the premise of the movie (as I understand it) is that we follow a dog over the course of several lifetimes and owners as he tries to discover his purpose. I think it is a question that many of us ask...”What’s our purpose?” We might ask the same of a paving grade asphalt binder...what is its purpose?

As asphalt technologists, we perform a lot of tests on paving grade asphalt binders and they all have a function related to the ultimate purpose of an asphalt binder – to be mixed with aggregate and placed on the road to serve as a smooth, quiet pavement.

We know that determining viscosity at 135°C using the rotational viscometer is part of the AASHTO M320 and M332 specifications to ensure pumpability at the asphalt mixing plant, but what about those requests to perform testing at 150°C and/or 165°C and/or 180°C? Well, those are requests related to the purpose of the asphalt binder by serving as a means to help us determine laboratory mixing and compaction temperatures that can be used in producing an asphalt mixture.

If the asphalt binder is unmodified, the use of the rotational viscometer at two temperatures is totally acceptable. You get viscosity results at two temperatures and then use that data to generate the appropriate mixing and compaction temperatures by plotting viscosity on a double-logarithmic scale (seriously) against temperature on a logarithmic scale. Where the temp-vis curve (actually a line) crosses a certain range of viscosity values is where we define the lab mixing and compaction temperatures. Pretty straightforward.

But what do we do with modified asphalt binders? The problem is that many polymer-modified asphalt binders have a substantial elastic component, even at high temperatures. So we can’t really use a method that only measures viscosity in the usual manner to get our test values. When we do, the results for laboratory mixing and compaction temperatures are often very high - out of the range in which we’d normally operate and, frankly, which could cause damage to the polymer if actually used when mixing in thinner films.

Fortunately, there are a couple of options available, both from a national research project, that offer different testing procedures for modified asphalt binders that result in lower, more realistic temperatures.

The Phase Angle Procedure uses the DSR and a frequency sweep (i.e., testing at a range of loading frequencies) test at a minimum of three high temperatures to create a mastercurve of phase angle. Once the mastercurve is created (at a reference temperature of 80°C) the reduced frequency is determined where the phase angle is 86 degrees. That value is input into a pair of empirical equations to get recommended lab mixing and compaction temperatures.

The Steady Shear Flow Procedure uses the DSR to perform a shear stress sweep in steady shear flow loading at a minimum of three test temperatures. The steady shear viscosity at 500 Pa is determined at each temperature and a standard viscosity-temperature graph is plotted (just like is done for unmodified asphalt binders). The temperature range where the steady shear viscosity reaches 0.32-0.38 Pa-s is the compaction temperature range. The temperature range where the steady shear viscosity reaches 0.15-0.19 Pa-s is the mixing temperature range.

According to the research, both methods produce comparable, lower mixing and compaction temperature ranges for polymer-modified asphalt binders than if the standard rotational viscosity procedure was used. Both are DSR tests that are easy enough to perform. Both require a little more testing and analysis than the standard rotational viscosity procedure. Either way, you’ll get values much closer to reality in allowing the polymer-modified asphalt binder to achieve its ultimate purpose.

For more information on testing of modified asphalt binders to determine lab mixing and compaction temperatures, please refer to NCHRP Report 648 (Mixing and Compaction Temperatures of Asphalt Binders in Hot-Mix Asphalt) and the AI website.

By the way, the first name of the director of “A Dog’s Purpose”? Lasse...of course.



TECH TIP

Zap to it


 
I’ve traveled to binder labs all over the U.S. and beyond and I’ve encountered, first hand, an impressive assortment of ‘work-arounds’. Many of these have found their way into our newsletter. This one is back by popular demand.

Why now? I’ve received a number of calls and emails asking where to find this great little gadget since it last had appeared. Also, having never seen one, many other technicians attending our binder classes have stared, at the red-hot talents of the Benchmark Scientific B1000 BactiZapper Laboratory Infrared Micro Sterilizer.

Try to trim a DSR specimen with a cold trimming tool. Ok, don’t. That would be silly. But you don’t have a gas source anywhere near the instrument… or you do and the burner is a pain to light or open flames are not allowed in your facility. So, you grab a propane torch or a BBQ lighter or a hot plate or any number of other random heat sources. Torches fall over, refuse to light and run out of gas. BBQ lighters take forever to heat and hot plates take up a lot of valuable bench-top real estate and are…hot and plate-like, mean and can burn you.

Just plunk down about $280 bucks, plug in the compact BactiZapper and set to low. Pop the trimming tool in the front and 5 short seconds later it will be perfectly heated. At the end of the day, turn it off and go home.   

- Mike Beavin, Asphalt Institute Technical Training Coordinator
 

TECHNICIAN SPOTLIGHT


Brendan McGillicuddy
Owens Corning Trumbull Asphalt
Quality Leader/Senior Quality Technician

Brendan has been working with asphalt quality control for over seven years. He tests asphalts for roofing, tests PG binders, calibrates and verifies equipment and trains new team members among other duties at his job.

He really enjoys working with the development of new asphalt products and educating team members about the cost of poor quality.

Brendan compares the NBTC program to the SHRP program in its success.

"NBTC has helped to standardize testing across the country," said McGillicuddy.  "I feel it helps us raise the bar—to produce a better product. A product customers can have a high confidence in because they are obtaining asphalt products of the highest quality."


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 41 states with users and/or producers who are nationally certified by the AI NBTC and the NETTCP programs. 
FREE TRAINING
Certification: What You Should Know About Training Binder Technicians (free)
Using the MSCR Test in Asphalt Binder Specifications (free)

(affordable technology, schedule at your convenience, pause-rewind-understand and email your questions)

 
BUY THE BOOK

Available in the Asphalt Institute online store. The second printing includes an Appendix on Multiple Stress Creep Recovery (MSCR) testing.
RECORDED WEBINARS
Asphalt Binder Series
Part 1 - Introduction
Part 2 - Testing & Specs
Part 3 - Testing & Specs (cont.)
Part 4 - Modification, Emulsions and Cutbacks
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