Date: January 1, 2010

News - Proper Cylinder Procedures

Cylinders are created for the purpose of the testing the compressive strength of concrete, concrete’s most common performance measure. Strengths reported to be low due to incorrectly tested concrete can be costly to everyone, as they result in job delays as well as additional expenses for extra testing. This is why it is crucial to ensure that cylinders are made and tested correctly. The only allowable methods for testing fresh plastic concrete are the American Society for Testing Materials (A.S.T.M.) Standards. Here are a few things to look out for to ensure that cylinders are made, cured and stored properly:
  • At minimum, the inspectors should be ACI Grade I certified.  
  • Sampling concrete from a truck mixer can only be done by obtaining the sample at two or more regularly spaced intervals during discharge of the middle portion of the load and then compositing them into one sample.  
  • Cylinders are made by filling in three layers of equal volume and rodding each layer 25 times. After each layer is rodded, tap the sides 10 to 15 times to close any holes left by rodding.  
  • Cylinders are then to be covered and placed in a protected environment within 15 minutes and not moved for 24 hours +/- 8 hrs.  
  • They are to be kept within a temperature range of between 60 to 80 degrees F.
  • A test result is the average of at least tow standard-cured cylinders made from the same concrete sample and tested at the same age. In most cases strength requirements for concrete are at an age of 28 days.
  • No single strength test should fall below the specified strength by more than 500 psi or by more than 10 percent of the specified strength when the specified strength exceeds more than 5000 psi.
When strength test results indicate that the concrete fails to meet the requirement of the specification, it is important to recognize that that the failure may be in the testing, not the concrete.  

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