The Knowledge & Equipment Needed to Perform a Concrete Compression Test

The Knowledge & Equipment Needed to Perform a Concrete Compression Test

28th Oct 2019

The concrete compression test is a simple procedure that can reveal a lot about the quality of a concrete sample, including the overall strength it will provide to the final structure and the adequacy of its curing. Most importantly, it ensures that the concrete meets the job's strength specifications and the quality measures outlined by the ASTM.

How Do You Determine the Compressive Strength of Concrete?

There are two general guidelines that must be followed when performing a concrete compression test: the average specified strengths of three consecutive tests should be equal to or greater than the strength specified for the job, and none of these strength tests should fall below the specified strength by more than 500 psi. Additionally, the concrete compression test should be performed according to the following steps, which are outlined in the ASTM C39 procedure.

  • Cylinders should still be moist when performing the test, so after removing them from a moisture room or other damp setting, quickly measure the diameters of each cylinder and record their weights (which can be useful if test results are in dispute later on).
  • Ensure that your test machine is clear of debris and set to zero.
  • Add either neoprene or sulfur mortar pad caps to the ends of your cylinders. Preferably, this should be done a day before testing.
  • Place your specimen into the testing machine and apply a load continuously, without shock, until the concrete fails or the machine has reached its ultimate capacity. 28-42 psi/second is a permissible rate for the first half of loading.
  • Remove the cylinder from the machine and take off the caps.
  • Calculate the strength of the cylinder (psi) by dividing the load when it failed (in pounds) by the area of the cylinder (in square inches).
  • Take note of the specimen's fracture patterns, which can help identify possible reasons for the failure. Certain types are acceptable, but others imply that there was a problem with concreting, uneven planing or the presence of a lubricant between the cap and the cylinder which affected the frictional forces at work.

What Equipment is Needed to Perform a Concrete Compression Test?

Equipment used for concrete compressive strength tests needs to be strong and stiff to reduce the possibility of explosive failures, which can shock the equipment's hydraulics and deteriorate its calibration — not to mention the general damage that could shorten its service life. It also needs to accommodate the pressure capacities to accurately determine the strength of the concrete you'll be testing.

The compression testing machines from Certified Material Testing Products have the durability and capacities needed for the job. Our machines range from 7,000-14,100 maximum psi for standard 6x12 concrete cylinders. They can also be equipped with digital controllers that display load, load rate, stress during the test and final load, and store the information to be plotted and printed later.

Aside from the concrete compression test machine itself, it's also important to employ compressometers for efficient data collection. Compressometers attach to the top and bottom of a concrete cylinder at opposite points to allow pivoting during compression. The digital gauge measures the average deformation and strain that concrete cylinders undergo during compression testing, which is useful if you are also testing for the modulus of elasticity.

Finally, it's always useful to have concrete compression test accessories to help your testing go as smoothly as possible. These could include concrete test cylinder wraps for protecting cylinders as they are transferred to the compression machine or a concrete cylinder lifting handle to help put the specimen securely into place. Each of these tools, and the many others that can be found in our inventory, will help produce the most accurate results and minimize slip-ups.

Get Your Concrete Compression Test Equipment at Certified MTP

If you need quality compressive strength testing machines or other concrete test equipment for your lab or facility, look no further than the extensive inventory of reliable products we have to offer. Have questions? Contact us today to learn more.

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