Concrete and pi
March 14, 2023 at 12:08 PM by Dr. Drang
Back in either 1980 or ’81, I took course called Properties and Behavior of Concrete, which had the course number CE 214 and this description:
Engineering properties of plain concrete; influence of cement, aggregates, water, and admixtures on the properties of fresh and hardened concrete; microstructure of cement paste and concrete; mix design; handling of fresh concrete; and behavior under various types of loading and environments. Laboratory practice is an important part of the course.
The University of Illinois’s civil engineering department has undergone course number inflation over the past 40 years. That course is now CEE 401, but the description is nearly identical:
Examination of the influence of constituent materials (cements, water, aggregates and admixtures) on the properties of fresh and hardened concrete, concrete mix design, handling and placement of concrete, and behavior of concrete under various types of loading and environment. Laboratory exercises utilize standard concrete test methods. Field trips are held during some scheduled laboratory sessions.
When I took the course, it was taught by J. Francis Young, whose book on concrete was still being copyedited (we students got photocopies of proofs with his handwritten corrections as handouts). Friends of mine who took it the following semester were taught by Clyde Kesler, the father of the concrete canoe, shortly before he retired.
The differences between Young and Kesler were striking. Kesler was a local boy, born and raised within a few miles of the university he got his degrees from and then spent his entire career at. Young was born in New Zealand, got his Ph.D. in London, and then had a long career in the middle of Illinois. They were brought together by concrete and academics.
What does this have to do with pi? During the part of the class on mix design, we learned how to proportion the water, cement, large aggregate (gravel), small aggregate (sand), and admixtures to get certain target properties in the concrete. During the mix design process, you do some calculations using the specific gravities of these constituents.
The specific gravity of portland cement is generally taken to be 3.15, but it’s not an exact figure. Prof. Young told us to just tap the π button on our calculators when we needed to enter it. This tip didn’t save us much time, but it was a great way to teach us the specific gravity of cement. In the 40+ years since taking that class, I’ve had to go through the mix design process only a few times, but every time I remembered to press the π button.