Hundreds of thousands of concrete cylinders are tested daily in the United States. Most tests are performed on manually operated concrete compression testing machines, which require an operator to control the rate of loading and record the results when the test is complete.
Manual Concrete Compression Testing Machines
The most common type of compression testing machine is hydraulically actuated and requires the operator to manually adjust a hydraulic valve during test to maintain the required loading rate.
Manual Compression Machine Equipped with an ADMET Indicator
Manually operated compression testing machines are widely used to determine the compressive strength of concrete. The testing of concrete according to ASTM C39 requires applying a compressive load at a rate of 35 psi/sec +/- 5 psi/sec to a cylindrical concrete specimen until it fails.
How ADMET Products Address Limitations of Manual Concrete Testing Machines
Manually operated concrete testing machines have several limitations, and these may impact the accuracy, efficiency, and reliability of the testing process. Below, we discuss the three limitations around manually operated concrete testing machines and how ADMET products and solutions overcome such limitations.
Limitation 1: Lack of Load Rate Verification & Control
Manual testing machines require the operator to continuously adjust a valve during the test so that the loading rate remains within the allowable limits as stipulated in the test specification followed. Manual operation is sufficient for most concrete testing applications, however, operator fatigue, insufficient operator training and operator error oftentimes results in tests performed at loading rates outside of the specified limits.
Read more about the effects of loading rate on the strength of concrete here.
Learn moreOur Solution: ADMET Concrete Testing System Retrofits
In order to verify that a test was performed at the required load rate, concrete testing machines require the use of digital indicators featuring one or more of the following:
- Display load and stress rates – provides feedback during the test for the operator adjusting the manual control valve
- Calculate the average load rate – provides post test verification that the test was performed properly
- Generate and store load/stress versus time curves – together with the average load rate calculation, storing this information provides a permanent record on how the test was performed
ADMET Digital Indicators for Concrete Testing
ADMET offers a full line of digital indicators for manually operated concrete testing machines. These indicators can be installed on new machines or retrofitted to existing machines in the field. Indicator selection is dependent on testing requirements and the table below outlines the important features of each indicator model.
ADMET Concrete Testing Indicators
Compression testing machines equipped with the right ADMET indicator have the capability to report the average loading rate, generate load and stress versus time curves, and verify that testing was performed within specification.
ADMET Servo-Control Retrofits
ADMET also offers conversion packages for manually operated concrete testing machines to upgrade them to full automatic servo control. These retrofit solutions eliminate the loading rate errors introduced by manually operated machines and ensure the test is performed according to specification. If more complex test profiles and calculations are required, ADMET can greatly extend the capabilities of your manually operated machine by retrofitting it with the MTESTQuattro Materials Testing System, a PC-based solution.
ADMET Retrofitted Systems
MTESTQuattro is also commonly used to upgrade/retrofit both manually operated and servo controlled testing machines manufactured by Baldwin, Tinius Olsen, Satec, Forney, Testmark, Instron, MTS, United and more – regardless of age, model, or machine type.
Read more about ADMET's Retrofit Options here.
Learn moreLimitation 2: Force Measurement Errors in Top Acting Concrete Testing Machines
Many concrete and cement strength tests are performed on machines with a top-acting hydraulically actuated piston. In order to retract the piston up (against gravity) to it’s mechanical stop, tension springs are installed on either side of the piston. Prior to a test, if the force is tared/zeroed at the mechanical stop or there is a gap between the compression platen and the test sample, the force readings will increase when the piston is pushed downward equal to the increasing spring tension. If the gap between the compression platen is large enough, this can result in measured compressive strength readings much higher than the actual strength of the material. One way to eliminate this error is to push the piston down to just before the compression platen touches the sample and tare/zero the force. This requires a well trained and alert operator to ensure force errors introduced by increasing spring tension are not introduced. For high throughput testing applications, it is a lot to expect an operator to properly perform the taring function prior to each test.
Our Solution: ADMET Gauge Buster 3 with Auto-Tare Force Feature
Compression Testing Machine with Top Acting Actuator Retrofitted with Gauge Buster 3
In order to eliminate the burden of the operator properly taring/zeroing the force before each test, ADMET has incorporated a first of it’s kind Auto-Tare Force feature into it’s Gauge Buster 3 Digital Indicator. The feature monitors the force vs time data just before and just after when the compression platen contacts the sample and automatically adjusts the zero force reading accordingly. This eliminates the need for the operator to tare the force reading before starting each test and ensures the measured compressive strength is accurate. Post test, the Gauge Buster 3 reports the compensated zero force reading and stores it as part of permanent test record. The Gauge Buster 3 Indicator is ideally suited for performing ASTM C39, ASTM C78, and ASTM C109 tests on a concrete compression testing machine and can be installed on new machines or retrofitted to existing concrete testing machines.
Limitation 3: Maximum Operating Pressure of Conventional Servo-Hydraulic Test Systems
The overwhelming majority of concrete testing machines are hydraulically actuated and require oil pressures approaching 68.9 MPa (10,000 psi) to achieve their specified force capacities. Conventional servo-hydraulic testing systems operate at a maximum hydraulic pressure of 31 MPa (4500 psi). Their inability to operate at oil pressures approaching 68.9 MPa (10,000 psi) and their higher costs preclude them from widespread use in concrete testing.
Our Solution: ADMET MegaForce – A Lower Cost Solution for a Automatically Controlled Concrete Testing Machine
Hydraulic Testing Machine equipped with ADMET’s MegaForce testing a cement cube
The MegaForce Testing System was developed in order to address the loading rate issues with manually-operated concrete testing systems and the high costs associated with conventional servo-hydraulic testing systems requiring larger more expensive actuators. By replacing the pump and manual control valve on a standard concrete testing machine with ADMET’s MegaForce, users can transform their machine into a servo controlled testing system capable of applying repeatable and accurate load/stress rates.
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.
Contact ADMET For Accurate Compression Testing Solutions
ADMET indicators and software have been the go-to product solutions for accurate and reliable test results in the concrete testing industry for over 30 years. We provide retrofit/upgrade packages that can significantly increase the accuracy and efficiency of your existing concrete testing machine.
To find the right product for your testing needs, contact us here.
If you’re interested in a new concrete testing machine, ADMET Concrete Testing Systems are capable of performing compression and flexural tests according to ASTM and ISO standards.
For all our Concrete Testing Machine offerings, click here.
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