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.
Our 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.
Limitation 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