ASTM C39 Compression Testing Concrete Cylinders

ASTM C39 has remained the industry standard for testing the compressive strength of cylindrical concrete specimens for more than 80 years. ASTM C39 covers the determination of compressive strength of cylindrical concrete specimens such as molded cylinders and drilled cores. 

The results of this test method are used as a basis for quality control of concrete proportioning and mixing, and are used by departments of transportation to ensure that concrete structures such as roadways and bridges are safe for travel and will adhere to their predicted lifespan. 

Specimen Preparation

Specimens are sampled from fresh concrete and mold cured in a cylindrical fashion for intervals ranging from 24 hours to 90 days. Specimens can also be drilled cores used to test the strength of a newly finished concrete structure or one that is showing signs of distress. ASTM C39 requires specimen measurements to be taken at three locations with the average being calculated and recorded. This test setup requires diligent operator care to ensure the specimens are aligned properly with the loading axis. To simplify this process and reduce the risk of operator miscalculation, an automatic specimen measurement device can be used.

Materials Testing System

ASTM C39 has updated the test control methods when crushing concrete. The speed of your testing is dictated by the control type, and it is important to make sure you are testing quickly and efficiently. The standard states that displacement-controlled devices test at different rates depending on the size of the specimens. Instron's 6800 Series floor models and industrial systems are capable of multiple test rate control. The system can either control the stress rate of your system for consistent validation and reduced specimen waste, or it can be configured with estimated stress rate and displacement control. Whichever mode of testing is configured, Instron's Bluehill Universal software can measure the load rate at a specified point in time to verify an acceptable rate of testing.

Test Setup, Procedure, and Calculations

ASTM C39 requires that the prepared concrete sample be placed on the lower platen of a compression testing system and carefully aligned with the loading axis (centered between the two platens). To ease the burden of handling heavy concrete specimens, Instron offers a loading device that helps to ensure operator safety and improve productivity. To meet the alignment requirements of this standard, we recommend using a spherically seated upper platen and a standard lower platen. The allowable diameter size of your platen will depend on the specimen size being tested. Instron offers a wide range of rigid and spherical platens for multiple diameters that are designed to be interchanged quickly and easily. If platens of multiple sizes are needed, 6800 Series systems can utilize auto positioning, a feature that enables the system to remember the fixture separation for each configuration.

ASTM C39 requires that test shutoff is prohibited until a value less than 95% of the peak load is reached. Bluehill Universal's end of test criteria can measure this to ensure that tests are not stopped preemptively. 

This standard also requires you to record the fracture type after specimen failure, and the standard outlines fracture types with a visual aid. Bluehill Universal includes an image guide in the C39 prompted test method to simplify your results recording.

ASTM C39 requires specimen measurements at three locations, with the average being recorded. To optimize this process and reduce a calculation step, the automated specimen measurement device can be used to automatically accommodate this measurement.

ASTM C39 has strict load reading requirements. Instron Load cells are capable of measure down to 1/1000th of the measuring capacities for multiple sizes of specimens.