🧱 Cement Compressive and Flexural Strength
Determination of compressive and flexural strength of standard cement mortar. Fundamental test qualifying cement to strength class (32.5 / 42.5 / 52.5).
Overview
Cement compressive strength is the main classification parameter for common cements per PN-EN 197-1. Testing involves preparing standard mortar prisms (cement : CEN standard sand : water = 1 : 3 : 0.5), curing in water, and testing flexural strength (3-point) and compressive strength on prism halves.
Cement strength classes after 28 days: 32.5 (≥32.5 MPa), 42.5 (≥42.5 MPa), 52.5 (≥52.5 MPa). Sub-classes R (rapid) and N (normal) distinguish early strength (2 days).
Standard PN-EN 196-1 is fundamental for cement quality control — every plant performs this test routinely. Results form the basis of Declaration of Performance (DoP) and CE marking of cement.
Method principle
Standard mortar: 450 g cement + 1350 g CEN standard sand (Normensand) + 225 g water, mixed in standard mixer (90 s slow + 30 s pause + 60 s fast). Molding in 3-gang molds 40×40×160 mm on jolting table (60 jolts). Curing: mold 24 h at RH ≥90%, then in water 20±1°C until testing.
Flexural testing: 3-point loading, support spacing 100 mm, rate 50±10 N/s → flexural force Rf. Compression testing: prism halves compressed on 40×40 mm platens, rate 2400±200 N/s → force Rc.
Applications
- Quality control of cement production (factory production control)
- Type certification of cement (type testing per PN-EN 197-1)
- Qualification of cement batches on construction sites
- Early (2 days) and late (28, 90 days) strength testing
- Comparative testing of cements from different producers
- Control of cement for special concretes (precast, HSC)
Key parameters
| Parameter | Value |
|---|---|
| Prism dimensions | 40 × 40 × 160 mm |
| Mortar proportions | C : S : W = 1 : 3 : 0.5 |
| Compression rate | 2400 ± 200 N/s |
| Flexural rate | 50 ± 10 N/s |
| Testing age | 2 days (R) and 28 days (standard) |
| Classes | 32.5 N/R / 42.5 N/R / 52.5 N/R [MPa] |
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. Weighing ingredients
Weigh 450±2 g cement, 1350±5 g CEN standard sand, and 225±1 g water (W/C = 0.50).
2. Mortar mixing
Cement + water → mix 30 s slow (140 rpm). Add sand within 30 s. Mix 30 s slow. Pause 90 s (scrape mortar). Mix 60 s fast (285 rpm).
3. Molding
Fill 3-gang mold in 2 layers. Compact each layer on jolting table (60 jolts). Level surface with trowel.
4. Curing I (mold)
Place mold in humidity chamber (RH ≥90%, T=20±1°C) for 24±1 h. Cover with glass plate.
5. Demolding
After 24 h demold prisms. Mark with date and number. Place in water 20±1°C.
6. Curing II (water)
Store in water 20±1°C until test day. Water must cover specimens min. 5 mm.
7. Flexural testing
Place prism on supports (spacing 100 mm). Load centrally at rate 50±10 N/s until fracture. Record force Ff.
8. Compression testing
Place prism halves between compression platens 40×40 mm. Load at rate 2400±200 N/s until failure. Record Fc.
9. Calculations
Rf = 1.5×Ff×l / b³ [MPa]. Rc = Fc / 1600 [MPa]. Average of 6 compression results (reject outliers >±10%).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Standard mixer | Controls 65-L0006, Toni Technik ToniMIX | 15,000–30,000 PLN |
| Jolting table | Controls 65-L0050, 60 jolts/cycle | 10,000–25,000 PLN |
| 3-gang molds 40×40×160 | Steel, PN-EN 196-1, Controls 65-L0060 | 1,000–2,500 PLN/pc |
| Cement press | Controls Automax Multitest, Toni Technik ToniNORM | 80,000–150,000 PLN |
| Humidity chamber | RH ≥90%, T=20±1°C, for 24 h mold storage | 10,000–25,000 PLN |
| Laboratory balance ±1 g | Radwag PS 4500 | 2,000–4,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| CEN standard sand (Normensand) | — | Quartz sand from Beckum (Germany), SN EN 196-1, 1350 g packs |
| Distilled/deionized water | — | For mortar preparation, 225 g per batch |
Health and safety (OHS)
- Cement — strongly alkaline (pH >12), irritates skin and eyes, gloves mandatory
- Cement dust — use FFP2 mask, work with ventilation
- Press — crushing hazard, do not insert hands in testing zone
- Jolting table — noise >85 dB, hearing protection