The concrete compression test is the primary measure of hardened concrete quality, determining the compressive strength used to verify mix design and structural acceptance.
What the Test Measures
Compressive strength is the maximum axial load a specimen carries divided by its cross-sectional area. EN 12390-3 uses 150 mm cubes (or cylinders); ASTM C39 uses cylinders. The result confirms whether concrete meets its specified characteristic strength class.
Apparatus Required
- Compression testing machine of adequate capacity and stiffness
- Cube/cylinder moulds and a curing tank
- Capping or grinding equipment for cylinder ends
- Calibrated load and platen system
NL Scientific manufactures the Computerized Compression Machine 3000 kN and the full concrete testing range, built to ASTM, EN, BS and AASHTO requirements with ISO/IEC 17025 accredited calibration.
Test Procedure
- Cast and cure specimens under controlled conditions (commonly 28 days).
- Measure specimen dimensions and check the bearing faces are plane.
- Centre the specimen on the lower platen of the machine.
- Apply load at a steady rate (0.6 ± 0.2 MPa/s for EN 12390-3) without shock until failure.
- Record the maximum load and note the failure pattern.
Calculation & Reporting
Compressive strength fc = Maximum load ÷ Cross-sectional area, reported in MPa (N/mm²). Report individual and mean strengths and the specimen age.
Acceptance Criteria
Acceptance is judged against the specified characteristic strength class (e.g. C25/30) using the conformity rules of EN 206 or the relevant code. Satisfactory failure patterns confirm a valid result.
Frequently Asked Questions
Cube or cylinder — which is correct?
EN practice commonly uses 150 mm cubes; ASTM uses cylinders. They give different numerical strengths, so always report the specimen type and standard.
Why does loading rate matter?
Loading too fast overstates strength and too slow understates it. A controlled rate keeps results comparable; computerised machines hold the rate automatically.
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