--- title: "Compressive strength test of cement" subject: "Civil Engineering Materials" chapter: 5 key: "semester_3/civil_engineering_materials:cement-compressive-strength-test" source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/cement-compressive-strength-test site: BCT Engineering --- # Compressive strength test of cement Civil Engineering Materials · Chapter 5: Cement - Asked in: 2081 Bhadra, 3 marks; 2078 Bhadra, 3 marks; 2074 Chaitra, 3 marks (asked 3 times) - Video: [HOW? | Test for Compressive Strength of Hydraulic Cement Mortar (ASTM C109)](https://www.youtube.com/watch?v=yjGrVpRw8Cw) — TeamCHEB - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/cement-compressive-strength-test - Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-5 ## Question Briefly illustrate the procedure to determine the compressive strength of cement in the laboratory. ## Short answer Mortar cubes (1:3 cement:sand) with water (P/4+3)% are cast in 70.6 mm moulds, vibrated, cured 1 day moist then water. Crushed at 35 N/mm²/min, strength = load/5000 mm². 53 grade OPC: 27 MPa (3 d), 37 MPa (7 d), 53 MPa (28 d). ## Answer The compressive strength of cement is found by crushing standard mortar cubes made from cement and standard sand (IS 4031 Part 6, IS 650). #### Apparatus Cube moulds of 70.6 mm side (area 5000 mm²), vibrating machine, standard (Ennore) sand, graduated cylinder, balance, curing tank, compression testing machine. #### Procedure 1. Take 200 g cement and 600 g standard sand for each cube, a 1:3 mix (for 3 cubes: 600 g cement + 1800 g sand). Mix dry for about one minute. 2. Add water equal to **(P/4 + 3)%** of the combined weight of cement and sand, where P is the percentage of water for standard consistency. Mix for 3-4 minutes until uniform in colour. 3. Place the mortar in the mould immediately and vibrate for 2 minutes at the specified speed; level and smooth the top. 4. Keep the moulds in a moist chamber at 27 ± 2 C and at least 90% relative humidity for 24 hours. 5. Remove the cubes and cure them in clean water at 27 ± 2 C until the test date. 6. Test the cubes at 3, 7 and 28 days after casting, on their sides, with a load rate of 35 N/mm² per minute. 7. Compressive strength = failure load / cross-section area (5000 mm²). The average of three cubes is the result. #### Minimum strength (53 grade OPC, IS 12269) | Age | Strength (MPa) | |---|---| | 3 days | 27 | | 7 days | 37 | | 28 days | 53 | For 43 grade (IS 8112) the values are 23, 33 and 43 MPa. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the mix used for each mortar cube in the cement strength test? A. 200 g cement and 600 g standard sand (1:3) B. 200 g cement and 200 g sand (1:1) C. 400 g cement and 400 g sand D. 100 g cement and 600 g sand Answer: A. A 1:3 cement:standard sand mix is used: 200 g cement with 600 g sand per cube. (Key point: Mix) 2. How much water is added to the mortar? A. 0.85 P of cement weight B. (P/4 + 3)% of combined weight of cement and sand C. 0.78 P of cement weight D. P% of sand weight Answer: B. P is the standard consistency percentage, and water is (P/4 + 3)% of cement plus sand. (Key point: Water quantity) 3. How is compressive strength obtained? A. Failure load multiplied by 5000 B. Single best cube result C. Failure load divided by 5000 mm2, averaged over three cubes D. Load divided by height Answer: C. Strength = failure load / area of 70.6 mm cube face (5000 mm2); mean of three cubes. (Key point: Strength calculation) 4. What is the curing and testing schedule for the cubes? A. Oven dry for 24 h; test at 1 day B. Air cure; test at 28 days only C. Boil 3 h; test at 7 days D. 24 h moist chamber at 27 C, then water curing; test at 3, 7 and 28 days Answer: D. Cubes stay 24 hours in a moist chamber at 27 +/- 2 C, are then cured in water and tested at 3, 7 and 28 days. 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