New instrument paddles the competition
By Mike Beavin
You arrive at the lab, grab a lab coat and safety glasses and scan the day’s testing load. A few flashpoints – you knock those out first thing. A million DSRs – no problem, just hit cruise control. A few other tests you have varying levels of enthusiasm about and then you see it, the test you’d rather have a root canal than perform: Saybolt viscosity. I’d probably no longer be employed at AI if this test was my primary responsibility. Why? Here’s an incomplete list:
1. The side squirt After cork removal, emulsion shoots sideways in defiance of the laws of gravity. Rerun test after doing a better job of Number 4.
2. The toilet flush Emulsion swirls down the receiving flask completely covering the timing mark. Rerun test after redoing Number 4.
3. The flask flop Pull cork, knock over flask and watch the emulsion shower. Rerun test after redoing Number 4 and much, much more.
4. The clean-up When you think you’re done, you usually aren’t. Likely cause of Number 1.
The Saybolt Furol test can be a headache, yes, but we needed a way to measure the flow properties of an emulsified asphalt. Until a few years ago, the test was the only accepted way to determine if there was a risk of emulsion run-off in chip seals, if it was thin enough to be sprayed but thick enough to stay where it was intended to be and if it would provide a proper film thickness on aggregate. For decades there was no competition until the paddle viscometer (PV) was introduced.
I first saw a demonstration of the paddle viscometer at an AASHTO conference a few years ago and immediately my ears perked up. The concept is simple. There is a cup to hold an emulsion sample, a rotating paddle, a torque transducer and a thermoregulation system. The paddle and the temperature probe are immersed in the emulsion sample and the paddle rotates. Once the appropriate sample temperature is reached, a viscosity reading is taken which can be converted (sort of) to Saybolt Furol Seconds (SFS). At the conclusion of the test, the paddle, cup and temperature probe can be cleaned with water and minimal solvents. Cleanup takes about two minutes and the whole process, start to finish takes about 20 minutes. On the other hand, a properly conducted Saybolt Furol test, cleaning included, takes a minimum of an hour. Finally, the entire PV unit occupies about the space of a toaster oven. It all sounded too good to be true.
Like any new-kid-on-the-block, the introduction of the paddle viscometer has met push-back. The early models didn’t have the excellent thermal control we see now. There have been reports of viscosity-related variability. Additionally, converted SFS values derived from the paddle viscometer tend to be slightly higher than those obtained with the Saybolt Furol test. The question I would ask is why are we asking for conversion to Saybolt Furol seconds in the first place? Familiarity? The loading modes for the two tests are completely different. The Saybolt Furol test relies on gravity and empirical test conditions while the paddle viscometer relies on an applied force and fundamental stress/strain relationships. We don’t see perfect correlations between the elastic recovery and MSCR tests for the same reasons. Ultimately, we are looking for an indication that an emulsion will flow as intended, not necessarily a specific viscosity unit.
The paddle viscometer seems to have gained traction. Both ASTM and AASHTO have published standards for the instrument. The push now is to make it an option, rather than a replacement for the Saybolt Furol viscometer, so you traditionalists out there have nothing to fear. Your cleaning time is secure.
TECH TIP
Mold around the collar
There are two interesting sections in “ASTM D139, Float Test for Bituminous Materials: Section 7.3” that discuss specimen pouring temperatures and section 7.7 which admonishes the technician against any funny business.
I’m pretty sure Shakespeare penned section 7.7. The dead giveaway is a discussion of whether tis nobler to suffer outrageous intentional spinning or to take arms against it. Nay, it clearly reads “Lateral drift of the assembly shall be permitted, but no spinning motion shall be intentionally imparted thereto.” I guess intentional spinning is particularly egregious because there is malice of forethought (I’m imagining an evil emulsion technician scanning the lab for witnesses before gleefully spinning the heck out of that float). Unintentional spinning is much more innocent, obviously, and thus shall be permitted.
Section 7.3 has less intrigue but does present a variety of problems. It rightfully notes that “The pouring temperature for high float emulsion residue can be critical.” What it fails to mention, however, is that reheating the residue to the correct pouring temperature often causes lower float times. I’m guessing that the act of reheating further damages the polymers needed to produce a high float residue. So, if I were boss, I’d require that float collars are poured from the still directly after the distillation is complete.
Problem: How many times have you poured a float collar from the still without making a huge mess? Never? Try this: grab an old silicone DSR mold and cut a hole in it with a cork cutter that’s slightly smaller than the pouring end of the float collar. Now fit it over the collar leaving a little space between the top of the collar and the surface of the mold and pour away. No more digging residue from the collar threads and no more worries about under-filled collars due to thermal contraction.
- Mike Beavin, Asphalt Institute Technical Training Coordinator
TECHNICIAN SPOTLIGHT
Maria Teresa Delgado Torres
Dynasol Group
Analytical Services Technician
Maria has been with Dynasol for five years - she was assigned to the asphalt lab two years ago. She is involved with asphalt binder applications that involve pavements, roofing and emulsions.
"The NBTC program was an incredible opportunity to reinforce my abilities in asphalt binder testing. The course gives you very detailed information not only about the testing, but also properties, background and the new developments." said Torres.