Lab Corner: Rheology is FUNdamental

By Mike Anderson, P.E.

For this article, I’m going back to my “when-I-was-younger” opening. I’m just providing some forewarning for our regular readers.

By the time you read this, summer will be on our doorstep. When I was a kid, summer vacation was the best. I don’t know how some kids deal with year-round school. I know it’s supposed to be better for knowledge retention, but they’re missing the pleasures of sleeping in almost every day, generally recuperating from the rigors of the primary and secondary education lifestyle.

Despite having the time in the summer to do nothing at all if I wanted, one activity that I loved was reading for fun (earlier Lab Corner articles have already firmly established my nerd standing so this should NOT be a shocker). Going to the library downtown was a treat…so many options. I’d check out 3-5 books at a time and plow through them.

Unfortunately going downtown to the library wasn’t always an option. That’s where the bookmobile would come in. What a great idea, books coming to me! I still remember one of the nonprofit organizations responsible for this treat – RIF – which was an acronym for “Reading is FUNdamental.” The “FUN” was capitalized. As a young man, I thought that was so clever. I mean, reading is fundamentally important… but it also is a lot of fun. What better way to get kids excited about reading than engaging in a little wordplay? Really excellent!

I’m older now and I still enjoy reading, but sometimes it’s about rheology (again, nerd). I think many of us hear “rheology” in connection with asphalt and our eyes start to glaze over a bit. No need for that. Rheology is the study of flow. That’s all. So, the rheology of asphalt is the study of how asphalt moves under different conditions of temperature, stress-strain, and loading time (or frequency).

Most often, we think about rheological measurements as being associated with mastercurves and reduced frequency and Arrhenius functions and Black Space. All true. But rheological measurements can simply be the standard dynamic shear rheometer (DSR) test we use to determine G*/ sin δ and the bending beam rheometer (BBR) test we use to determine low-temperature stiffness and m-value. It’s just that the standard BBR and DSR tests that we often use are used to get us point values, describing the behavior of the asphalt binder at a specific temperature and frequency (or time). While that is important for comparing two binders or determining how the asphalt binder properties compare to the specification, we can get so much more information about the behavior of the asphalt binder in relatively little time by testing at multiple temperatures and frequencies (or loading times). That’s where the shifting and mastercurves and Black Space come in. It just takes a little education to know how to use that information.

There are some very good resources out there to learn more about rheology. One option is to check with your DSR equipment manufacturer. They’re specialists in all things rheology, not just asphalt materials. Another option is to check out a Rheobit class near you. Created and conducted by Dr. Geoff Rowe, an expert in asphalt rheology, the course really digs into the details of the rheological behavior of asphalt materials. To find out more, just go to your set of encyclopedias and…oh, sorry; still stuck back in time. Try the internet.

I think you’ll find that rheology of asphalt materials is fundamental and maybe fun as well. As I said earlier, so clever.

Mike Anderson is the Director of Research and Laboratory Services at the Asphalt Institute.

For information on Asphalt Institute’s laboratory training, research, and testing services email Mike Anderson or Gary Irvine