ASTM C39 Concrete Cylinder Compression Testing

Summary of Test

ASTM C39 determines the compressive strength of cylindrical concrete specimens such as molded cylinders and drilled cores. It is limited to concrete having a unit weight in excess of 50 lb/ft3 (800 kg/m3).

A compressive axial load is applied to molded cylinders or cores until failure occurs. The compressive strength of the specimen is calculated by dividing the maximum load achieved during the test by the cross-sectional area of the specimen. The results of this test method are used as a basis for quality control of concrete. 

Before conducting ASTM C39, it is important to read the entire specification in the relevant ASTM publication.

Testing Procedure

1. Place the specimen on the lower bearing block so the axis of the specimen is aligned with the center of thrust of the spherically seated bearing block.
2. Make sure the load indicator is set to zero prior to starting the test.
3. Apply a compressive loading rate of 35 ± 7 psi/s (0.25 ± 0.05 MPa/s) continuously and without shock until failure or until the operator is certain that the ultimate capacity has been achieved.
4. Record the maximum load/stress carried by the specimen during the test and note the type of fracture pattern.

Concrete Load Rate Sensitivity

The compressive strength of concrete is sensitive to loading rates; at higher loading rates the compressive strength increases. One study found a 2.6% increase in compressive strength when the loading rate increased from 0.14MPa/s (20 psi/s) to 0.34MPa/s (50 psi/s).[1] As a reference, those rates are just outside the lower (0.2 MPa/s) and upper (0.3 MPa/s) limits allowed by ASTM C39.

The overwhelming majority of concrete testing systems are manually operated. Here a machine operator adjusts a needle valve to control the rate of loading. Even if a machine has the ability to indicate loading rate the operator needs to remain attentive throughout the test in order to adjust the needle valve and maintain the specified loading rate. The high volume of compressive strength tests a lab needs to test on a daily basis provides an incentive to complete tests as quickly as possible. Without the proper process controls in place, there is no way to ensure tests were performed properly which may result in reporting inaccurate compressive strength results.

The presence of load rate sensitivity in concrete demands that tests be performed on machines capable of accurate and repeatable control rates and that are capable of reporting verifiable compressive strength results. ADMET offers the DFG Concrete Indicator and the Gauge Buster 3 indicator to retrofit manually operated concrete testing machines for consistent and accurate testing of concrete cylinders, beams, and cement cubes in accordance with AASHTO and ASTM standards. Both digital indicators include load rate indication necessary for the operators to adjust the needle valve during the test to maintain the specified loading rates. Post-test, the DFG and GB3 Digital Indicators will calculate and report the average loading/stress rate which is paired and stored with the compressive strength result. Users can then export the test results from the digital indicator to a pc running ADMET’s GaugeSafe Data Exchange program and save the results to disk thereby creating a permanent record and proof that the tests were performed according to specification.

The DFG and the Gauge Buster 3 Digital Indicators come equipped with specific features for concrete testing:

• ASTM C39 cylinder correction factor to automatically adjust compressive strength readings according to the length-to-diameter ratio
• Load rate and stress rate indication with a real-time numerical or graphical display that enables operators to adjust the manual loading valve during test and stay within the specified rate limits
• Calculate and store average stress rate to permanent memory. Provides verification that each test was performed according to specification.
• User-selectable units of force per minute, force per second, stress per minute, and stress per second to provide feedback to the operator for the adjustment of the test rate in accordance with ASTM requirements
• Report Specimen type/geometry to facilitate compressive and flexural strength measurements
• Store date, time, specimen size, specimen age, specimen weight, cylinder cap type, and cylinder break type with each compressive strength and average stress rate result in memory and quickly switch between types of tests and samples (6×12 cylinders, 4×8 cylinders, 2 inch cubes or beams)
• Download test results including specimen information to a computer for easy import into common spreadsheet programs or a company database designed to generate compressive strength reports for their clients

ADMET CONCRETE INDICATORS

Retrofit/Upgrade Packages to Convert Manually Operated Testing Machines to Automatic Control

ADMET offers retrofit packages to upgrade existing testing frames for more accurate control and reporting to perform ASTM C39.

MegaForce Concrete Testing System

The MegaForce Testing System is a low-cost solution for converting your manually operated concrete testing machine to automatic control. Once installed, the MegaForce Testing System with GB3 Digital Indicator provides load/stress rate automatic closed loop servo control. The upgraded solution is then capable of performing accurate repeatable tests (ASTM C39, C78, C109) according to specification with minimal operator interaction.

Hydraulic Testing Machine equipped with ADMET’s MegaForce testing a cement cube

The MegaForce Concrete Testing System works with compression machines that operate up to 69 MPa or 10,000psi. Depending on the indicator chosen with the system, automated compressive strength test reports are generated, saving time as well as costs required to manually generate reports while decreasing the chance of errors.

Learn more about the importance of choosing the right type of controller: Open-Loop vs Closed-Loop Systems in the Materials Testing Industry

Servo-Control Retrofit with MTESTQuattro Package

MTESTQuattro® is an advanced materials testing system for servo-hydraulic and electromechanical testing machines. Its unique design consists of a PC-based application program and an easy-to-install external interface box which makes MTESTQuattro well-suited for new and retrofit installations. Our retrofit packages are compatible with existing testers including Tinius Olsen, Satec, Forney, and Instron- regardless of age, model, or machine type.

YOUR RETROFIT OPTIONS

Universal Testing Machines Capable of Performing a Wide Range of Concrete Tests

ADMET’s versatile universal testing machines provide a lot of benefit as an all-in-one solution for any kind of concrete testing including tension, compression, and flexion with automated control and strain-rate feedback. Some of the tests that fall into this category include ASTM C307, ASTM C469, ASTM C1609, and EN 14651.

eXpert 2657 (300 kN) – With ASTM C1609 fixturing and optional computer

Both the eXpert 2600 electromechanical and the eXpert 1600 servo-hydraulic universal testing systems can be equipped with a variety of accessories including basic compression platens or spherically seated compression platens for ASTM C39 and ASTM C109, the compressometer-transducer assembly for ASTM C469, and the bend fixture assembly with two transducers for ASTM C1609.