Compressive Strength of Cement
Compressive Strength Test of Cement Mortar Cubes – IS 4031 (Part 6) | Step-by-Step with Examples Compressive Strength Test of Cement Mortar Cubes (IS: 4031 – Part 6) 1. Object of the Test To determine the compressive strength of hydraulic cement using standard cement mortar cubes (70.6 mm) compacted by a standard vibration machine as per IS 4031 (Part 6). Quick Summary: IS:4031 (Part-6) specifies the method for determination of compressive strength of cement using standard mortar cubes of size 70.6 mm. Cubes are prepared in a 1:3 cement–standard sand mix, compacted by vibration, cured for 3, 7 and 28 days, and tested at a loading rate of 35 N/mm²/min. The test ensures that cement meets the minimum strength requirements prescribed for OPC-43 and OPC-53 grades. See calculation & examples → Example: This test is used to check whether an OPC 43 or OPC 53 cement bag supplied to site meets BIS strength requirements at 3, 7 and 28 days. 2. Apparatus Vibration machine (12,000 ± 400 vibrations/min) Cube moulds – 70.6 mm × 70.6 mm × 70.6 mm Standard sand (IS 650 : 1966) Prodding rod Non-porous mixing plate Weighing balance Cube crushing testing machine (CTM) Mould oil, petroleum jelly Potable / distilled water Example: If your CTM capacity is 2000 kN and vibration machine speed is calibrated annually, the setup satisfies IS requirements. 3. Standard Sand (IS 650) Particle Size Range Percentage 2.0 mm – 1.0 mm 33.33% 1.0 mm – 500 micron 33.33% 500 micron – 90 micron 33.33% Example: If 900 g of standard sand is tested for gradation, each fraction should weigh approximately 300 g. 4. Mix Proportion Material Quantity Cement 200 g Standard Sand 600 g Water (P/4 + 3)% P = % water required for standard consistency (IS 4031 Part 4) Example: If standard consistency P = 26% Water = (26/4 + 3)% = 9.5% Total mass = 800 g Water = 0.095 × 800 = 76 g 5. Mixing Procedure Dry mix cement + sand for 1 minute. Add calculated water. Mix for minimum 3 minutes. Reject mix if uniform colour is not achieved within 4 minutes. Example: Dry mixing from 10:00–10:01 AM Wet mixing ends at 10:04 AM → ACCEPTABLE If mixing continues beyond 10:05 AM → REJECT batch 6. Moulding of Specimens Oil mould and base plate. Fix mould firmly on vibration table. Fill mortar in layers. Prod each layer 20 times in ~8 seconds. Vibrate for 2 minutes. Finish surface using trowel. Example: 1st layer: 20 rod blows in 8 s 2nd layer: 20 rod blows in 8 s Vibration time: 2 minutes exactly 7. Curing of Specimens Keep moulds in moist room for 24 hours. Demould and immerse in water. Maintain water temperature at 27 ± 2°C. Renew water every 7 days. Example: Casting completed at 4 PM on Day-0 Demould at 4 PM on Day-1 3-day test conducted at 4 PM on Day-3 8. Testing of Specimens Test cubes on their sides. Load rate: 35 N/mm² per minute. Test minimum three cubes. Example: For cube area 50 cm² (=5000 mm²), Load rate ≈ 175 kN per minute 9. Calculation of Compressive Strength Compressive Strength = P / A Example (kg-machine): Crushing load = 7200 kg Area = 50 cm² Strength = 7200 / 50 = 144 kg/cm² Example (kN-machine): Load = 720 kN Equivalent load = 720 × 101.97 = 73418 kg Strength = 73418 / 50 = 1468 kg/cm² 10. Minimum Strength Requirements OPC 43 Grade Cement Age Strength (MPa) kg/cm² 3 Days 23 235 7 Days 33 337 28 Days 43 438 OPC 53 Grade Cement Age Strength (MPa) kg/cm² 3 Days 27 275 7 Days 37 377 28 Days 53 540 ⬇ Download Cement Mortar Cube Test – Excel Sheet Top 10 FAQs – Compressive Strength of Cement What is the compressive strength of cement? It is the maximum load per unit area that a cement mortar cube can withstand under compression. Which IS code governs the compressive strength test of cement? IS:4031 (Part-6) specifies the procedure for determination of compressive strength of cement. Why is standard sand used in cement strength testing? Standard sand (IS:650) ensures uniform grading and repeatable test results. What is the size of cement mortar cube? Standard cube size is 70.6 mm × 70.6 mm × 70.6 mm with a cross-sectional area of 50 cm². What is the mix proportion for cement mortar cubes? Cement : Standard Sand = 1 : 3 by weight. How is water quantity calculated? Water = (P/4 + 3)% of the combined weight of cement and sand, where P is the standard consistency. What are standard curing periods? Cement mortar cubes are tested at 3 days, 7 days, and 28 days. What is the required compressive strength for OPC cement? OPC-43: 23, 33, 43 MPa and OPC-53: 27, 37, 53 MPa at 3, 7, and 28 days respectively. How is compressive strength calculated? Strength (kg/cm²) = Crushing Load (kg) / Area (cm²). Can a compression testing machine display load in kN? Yes. Load in kN must be converted into kg before calculating strength. Prepared by Kishor Kumar | Source: HighwayQualityTest.com Standard Reference: IS 4031 (Part 6) – Methods of Physical Tests for Hydraulic Cement (BIS). Quick Reference: Compressive Strength of Cement (IS:4031 Part-6) Test Objective: Determine compressive strength of standard cement mortar cubes Specimen Size: 70.6 mm × 70.6 mm cube (area = 50 cm²) Mix Proportion: Cement : Standard Sand = 1 : 3 by weight Quantity per Cube Set: Cement = 200 g, Sand = 600 g Water Content: (P/4 + 3)% of combined mass of cement and sand Standard Sand: Conforming to IS:650 (100% passing 2 mm, retained on 90 micron) Compaction: Vibration for 2 minutes @ 12,000 ± 400 vibrations/min Curing Periods: 3 days, 7 days & 28 days Loading Rate: 35 N/mm²/min during compression test Formula: Compressive Strength = P / A (kg/cm²)
