🏗️ Concrete Compressive Strength

Construction PN-EN 12390-3

Overview

Compressive strength is the most important mechanical parameter of concrete, determining its class (e.g., C20/25, C30/37). The test involves loading a specimen (150 mm cube or ø150×300 mm cylinder) with a compressive force at constant rate until failure.

Concrete class (e.g., C30/37) means: 30 MPa — cylindrical strength (fck,cyl), 37 MPa — cubic strength (fck,cube). Standard PN-EN 12390-3 is essential for quality control of concrete production (plants) and site control (acceptance). Results form the basis for confirming concrete compliance with design specifications.

Testing is performed after 28 days of curing (standard) or at any concrete age (early strength — 7 days, later — 56/90 days). Specimens cure under standard conditions: water 20±2°C or climate chamber 20±2°C, RH ≥95%.

Method principle

A concrete specimen (cubic or cylindrical) is placed centrally on the lower platen of a hydraulic press. Load is applied at constant rate 0.6 ± 0.2 MPa/s (for class ≤C50/60) until specimen failure. Maximum force (Fmax) divided by cross-sectional area gives compressive strength:

fc = Fmax / Ac [MPa]

where Ac — specimen cross-sectional area (for 150 mm cube: Ac = 22,500 mm²). Result is rounded to 0.1 MPa.

Applications

• Quality control of concrete in plants (compliance with PN-EN 206)
• Concrete acceptance on construction sites — class confirmation
• Assessment of early strength (7 days) for formwork removal
• Diagnostic testing of existing structures (drilled cores)
• Quality control of precast concrete products
• Quality documentation for infrastructure construction (bridges, tunnels)

Key parameters

Standard

Standard number

PN-EN 12390-3:2019

Title (PL)

Badania betonu — Część 3: Wytrzymałość na ściskanie próbek do badań

Title (EN)

Testing hardened concrete — Part 3: Compressive strength of test specimens

Step-by-step procedure

1. Specimen sampling

   Collect concrete from mixer/pump per PN-EN 12350-1. Fill molds in 2 layers, compacting each (vibrating table or rod). Level surface.

   ⏱ Time: 15 min

2. Initial curing

   Cover molds with plastic sheet. Store 16–72 h at temp. 20±5°C. Then demold.

   ⏱ Time: 24 h • 🌡 Temperature: 20±5°C

3. Standard curing

   Place specimens in water 20±2°C or climate chamber (RH ≥95%, T=20±2°C) until 28 days.

   ⏱ Time: 28 days • 🌡 Temperature: 20±2°C

4. Test preparation

   Remove specimen from water. Surface dry. Measure dimensions (±0.1 mm). Weigh. Calculate density. Check perpendicularity and flatness of faces.

   ⏱ Time: 10 min

5. Surface capping

   If surface uneven — apply capping layer (sulfur or neoprene). Ensure parallel contact with press platens.

   ⏱ Time: 15 min

6. Compression

   Place specimen centrally on lower press platen. Load at constant rate 0.6±0.2 MPa/s without shocks until failure. Record maximum force Fmax.

   ⏱ Time: 2–5 min

7. Failure assessment

   Check failure pattern — should be satisfactory (double cone). Reject results with unsatisfactory failure (lateral splitting, twisting).

   ⏱ Time: 2 min

8. Calculations and report

   fc = Fmax / Ac. Calculate for each specimen. Compare with required concrete class. Prepare test report.

   ⏱ Time: 10 min

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Hydraulic press — crushing hazard, do not insert hands in compression zone
• Specimen failure — fragments may eject, use protective shields
• Specimen weight (~8 kg cube) — lifting ergonomics
• Sulfur (capping) — heated to ~130°C, burn risk and SO₂ fumes
• Safety glasses and gloves mandatory

Training and video materials

• Concrete Cube Compression Test — Controls Group (Source: Controls)

Frequently asked questions