Concrete Compression Test: Equipment Needed

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?

Two general guidelines 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 6×12 concrete cylinders. They can also be equipped with digital controllers that display load, load rate, and 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 also test for the modulus of elasticity.

Useful Accessories for Concrete Testing

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.

The Concrete Compression Test is a fundamental and widely used method in civil engineering to determine the compressive strength of concrete. This test ensures that concrete structures like buildings, bridges, and roads meet the required safety and quality standards.

Principle and Equipment:

The test involves applying a compressive axial load to a concrete specimen, usually a cylinder or cube, until it fails. The equipment used for this test is a hydraulic press, designed to apply controlled and gradual pressure. The specimen, prepared and cured under standard conditions, is placed between the platens of the testing machine. The load is then applied at a specified rate until the specimen fails, and the maximum load applied is recorded.

Procedure:

Concrete specimens for the test are typically cylinders (150mm diameter and 300mm height) or cubes (150mm x 150mm x 150mm). These samples are cast from fresh concrete and are cured for a specified period, usually 28 days, before testing. During the test, the specimen is loaded until failure occurs. The load at which the concrete specimen breaks is noted and the compressive strength is calculated by dividing this load by the cross-sectional area of the specimen.

Applications:

The Concrete Compression Test is crucial in the construction industry for quality control purposes. It ensures that the concrete mix design meets the required strength specifications for different construction projects. It is also used in research and development for testing new concrete mixtures.

Advantages and Limitations:

The main advantage of this test is that it provides a direct measurement of concrete strength. However, the test is destructive and requires careful specimen preparation and curing for accurate results. Additionally, the strength obtained is specific to the specimen and may not represent the overall strength of a structure.

In summary, the Concrete Compression Test is a critical assessment tool for understanding the strength properties of concrete. It provides essential data for the safe and effective design and construction of concrete structures, ensuring they meet necessary strength standards.