🧱 Cement Strength
Determination of cement compressive and flexural strength on 40×40×160 mm standard mortar prisms. Basis for cement classification into strength classes.
Overview
Testing of cement compressive (and optionally flexural) strength is a fundamental test in binding material technology. The 28-day result forms the basis for classifying cement into strength classes (32.5; 42.5; 52.5 MPa) and early strength subclasses (N — normal, R — high). Testing is performed on standard mortar prisms of dimensions 40×40×160 mm.
Standard PN-EN 196-1 precisely specifies standard mortar composition: 450 g cement + 1350 g standard sand (CEN) + 225 g water (w/c = 0.50). CEN standard sand is certified natural quartz sand with strictly defined grading, produced by designated laboratories (e.g., SNL in France, Normensand GmbH in Germany). Use of non-standard sand invalidates the result.
Mortar is mixed in automatic mixer according to strict time program, molded in three-part molds and compacted on jolting table (60 cycles in 60 s). After demolding (after 24 h), prisms are stored in water at 20 ± 1°C until test day (2 or 7 days — early strength, 28 days — normal strength).
Testing is mandatory in factory production control of cement (FPC), conformity assessment per PN-EN 197-1 and product certification. Cement plants perform this test daily. Testing laboratories perform it as part of market surveillance and proficiency testing (PT).
Method principle
Standard mortar prisms 40×40×160 mm, after appropriate curing time, are first tested in flexure, then the resulting halves in compression. In flexural test, prism is placed on two supports (100 mm spacing) and loaded with concentrated force in middle of span at rate of 50 ± 10 N/s. In compression test, prism half is placed between two 40×40 mm compression platens and loaded at rate of 2400 ± 200 N/s. Compressive strength Rc = Fc/1600 [MPa], where Fc — failure force [N].
Applications
- Classification of cement into strength classes (32.5; 42.5; 52.5 MPa)
- Factory production control of cement (FPC per PN-EN 197-2)
- Assessment of cement conformity with standard PN-EN 197-1
- Type testing (ITT) of new cement types
- Proficiency testing (PT/ILC) of cement laboratories
- Quality control of special cements (sulfate-resistant, low-heat)
Key parameters
| Parameter | Value |
|---|---|
| Prism dimensions | 40 × 40 × 160 mm |
| Mortar composition | 450 g cement + 1350 g CEN sand + 225 g water |
| Loading rate (compression) | 2400 ± 200 N/s |
| Loading rate (flexure) | 50 ± 10 N/s |
| Curing conditions | Water 20 ± 1°C |
| Test ages | 2 days (early R) or 7 days (early N) and 28 days |
Standard
- Standard number
- PN-EN 196-1:2016
- Title (PL)
- Metody badania cementu — Część 1: Oznaczanie wytrzymałości
- Title (EN)
- Methods of testing cement — Part 1: Determination of strength
Step-by-step procedure
1. Material preparation
Temper cement, sand and water to 20 ± 1°C. Weigh: 450 ± 2 g cement, 1350 ± 5 g CEN sand, 225 ± 1 g water.
2. Mold preparation
Clean three-part molds. Apply mold release oil. Mount on jolting table. Check tightness.
3. Mortar mixing
Pour water into mixer. Add cement. Mix 30 s (slow). Add sand over 30 s. Mix 30 s (fast). Pause 90 s. Mix 60 s (fast).
4. Prism molding
Fill molds with mortar in two layers. After each layer, compact on jolting table (60 jolts in 60 s). Level surface.
5. Initial curing
Place molds in humidity chamber (20 ± 1°C, RH ≥90%) for 24 h. Cover with glass plate.
6. Demolding
After 24 h carefully demold prisms. Mark (number, date). Place in water bath 20 ± 1°C.
7. Water curing
Store in water 20 ± 1°C until test day. Water must cover prisms min. 5 mm. Change every 2 weeks.
8. Flexural strength testing
Remove prism from water. Place on supports (100 mm). Load at 50 ± 10 N/s rate until failure. Record failure force Ff.
9. Compressive strength testing
Place prism halves between 40×40 mm platens. Load at 2400 ± 200 N/s rate until failure. Record force Fc.
10. Results calculation
Rf = 1.5 × Ff × l / b³ [MPa] (flexure, l=100 mm, b=40 mm). Rc = Fc / 1600 [MPa] (compression). Result = average of 6 compression values.
11. Assessment and classification
Compare Rc28 with PN-EN 197-1 requirements: class 32.5 (≥32.5 MPa), 42.5 (≥42.5 MPa), 52.5 (≥52.5 MPa). Check Rc2 or Rc7.
12. Documentation
Prepare report: cement type, mixing date, curing conditions, Rf and Rc results, classification.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Cement prism press | Controls Autotest 300, Matest E161/E159, TZB-130 (ARHO) | 40 000–150 000 PLN |
| Flexural testing attachment | Support spacing 100 mm, rate 50 ± 10 N/s | 5 000–15 000 PLN (included with press) |
| Automatic mortar mixer | Controls 65-L0005, Matest E093 — mixing program per PN-EN 196-1 | 8 000–20 000 PLN |
| Three-part molds 40×40×160 mm | Steel per PN-EN 196-1, Controls, Matest | 1 500–4 000 PLN/pc |
| Jolting table | Controls 65-L0030, Matest E095 — 60 jolts in 60 s | 5 000–12 000 PLN |
| Thermostatic water bath | Controls 65-L0006 — 20 ± 1°C, capacity min. 100 L | 3 000–10 000 PLN |
| Laboratory balance | Radwag PS 6000/C/2, accuracy 1 g, range to 6000 g | 2 000–5 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| CEN standard sand (EN 196-1) | — | Certified quartz sand, grading 0.08–2.0 mm, 1350 g packs, producer: SNL/Normensand |
| Test cement | — | Cement sample taken per PN-EN 196-7, stored in sealed container |
| Distilled or deionized water | — | For preparing mortar (225 g per batch) and filling curing tank |
| Mold release oil | — | Thin layer on inner mold surfaces — facilitates prism demolding |
Health and safety (OHS)
- Testing press — crushing hazard, use protective guards
- Cement — irritating to skin and eyes (pH>12), gloves and safety glasses
- Cement dust — use FFP2 mask when weighing and mixing
- Mortar fragments during failure — safety glasses
- Hot water (optional) — for accelerated testing