How to Mold Concrete Cylinder
To make sure contractors meet the standard specifications of concrete a series of tests are ran. Cylinders are molded in order to crush on a machine to make sure they are the correct compressive strength.
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Things You'll Need
- 6 X 12 or 4 X 8 cylinder mold
- round tamping rod or vibrator
- rubber mallet
- cylinder lid
- hand trowel (optional)
Instructions
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First you need to collect a sample of concrete from the source. The sample of concrete should be taken from the stream as it is being poured out. You want to collect a representative sample of the mix. At least 1/4 of the mix should be emptied off the truck. To run all of your tests and according to standards you need 1 cubic ft of mix. After mix is sampled take it to the location for sampling.
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The concrete needs to be remixed before test is ran. After collecting mix you have 5 min. to test the mix and 15 min to start molding the cylinders. After you have mixed it up using your scoop it is time to begin the test. If the concretes slump is less than 1" a vibrator is required for consolidation, between 1 and 3" you can rod or vibrate, and more than 3" rodding is required. If using the vibrator concrete is to be placed in 2 equal lifts vibrated between lifts. If using the rod the cylinder needs to be filled in three equal lifts. After you place one third in the cylinder mold you need to rod the concrete vertically 25 times using the tamping rod. After rodding you use the rubber mallet and hit around the edge of the mold for a total of ten times. Repeat this for the final two lifts. The third lift should have extra concrete sticking above the lip approx a quarter inch.
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After rodding the third and final lift the top needs to be neatly screeded off. Using either the tamping rod or the hand trowel the top needs to be neatly cleaned. If you are using the tamping rod using a sawing motion while rolling the rod across the top of the cylinder. If using the hand trowel you strike off the top and use a sawing motion to make it smooth and void less.
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Tips & Warnings
Use water to keep your equipment clean and keep the concrete from sticking
Using water on the surface of the cylinder will give you a nice clean finish.
concrete must be protected from elements at all times
cap cylinders immediately after finished molding
