Concrete Compression Testing

One of the four engineering classes I’m taking this semester is Civil Engineering Materials (CEE 123).  This is the first year it is being taught as the materials requirement used to be satisfied through MAT 033.  Now instead we get to learn about things civil engineers actually use in the field rather than polymers and synthetic materials that were taught in the Material-Science class.  Our professor has been really good about laying out the course detail, incorporating a lot of hands on labs based off of calculations we did on our own.

The focus of the first third of our semester has been on concrete.  Each week, the lab groups have done a specific step in designing a batch of concrete.  First, we determined the moisture content of the aggregate stone and sand given to us.  We then did the calculations to find the correct proportions of materials that should be mixed into our concrete batch.  These materials included the aggregate, sand, cement, and stone and were all dependent on what compression strength we wanted, the moisture content of the solids, the type of cement used, the ideal slump, etc.  After mixing the concrete ourselves, we did a slump test to quantify the flowablility of the mix and molded nine 4×8 in. cylinders and one 6x6x24 in. beam.  The next week we made 2 separate mortar mixes based off of our own calculations and molded them into 6 2×2 in. cubes.

Finally this week, we did compression testing on the cylinders and cubes we made.  You’ll never be more happy to see something you made break!  We recorded the maximum force the concrete withstood before it failed after measuring the average diameter, so that the Imagemaximum axial compression stress could be calculated as the force over the cross-sectional area.  The picture here shows how it was all done; the thin plates around the top and bottom of the cylinder are sulfur caps that we molded on to make the surfaces as parallel as possible (this reduced any sideways shearing force that might have acted on our specimen).  Our three cylinders held up to about 55,000 pounds of force, which would correspond to roughly 1,100 psi.  Although our group had one of the strongest concretes, it was still very low due to the high amount of water we added to our mix accidentally.  Some of the other groups accidentally used mortar cement mix for their concrete cylinders which has a much lower strength.  The mistakes that were made just showed everyone how important the calculations are in designing something as fundamental as concrete.  Our professor has had us strictly follow ASTM standards, which outline pretty much how everything is required to be tested in the civil engineering world.  Overall, the class is very interesting and hands-on; you literally get you hands dirty in the things you will probably use when working out in the field.


About lukarl15

Hey! I'm Karl, a civil engineer in my senior year at Lehigh University. I am from the Buffalo/Western New York area and am the president of the American Society of Civil Engineers on campus. I am also on the Running Club team, practice electric and classical guitar, and study music theory on my own. I enjoy playing and watching sports with my friends in my free time (or the times when I probably should be studying). View all posts by lukarl15

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