Overview

Compressive strength of cement is determined by compressive strength test on mortar cubes compacted by means of a standard vibration machine. Standard sand (IS:650) is used for the preparation of cement mortar. The specimen is in the form of cubes 70.6mm*70.6mm*70.6mm.

Apparatus

Measuring Instruments

NAME	CAPACITY / RANGE / SIZE	ACCURACY / LEAST COUNT
Cube mould	70.6*70.6*70.6 mm3(IS:10080)	—
Vibration machine	Should be as per IS:10080	—
Balance	1000 g	1 g
Measuring cylinder	200 ml	1 ml

Other Apparatus

Enamel tray, Trowel, Poking rod

Environmental Conditions

Temperature	27 ± 20 C
Humidity	65 ± 5 %

Test Procedure

1. Take 200 g of cement and 600 g of standard sand and mix them dry thoroughly.
2. Add  of water  (where P is % of water required for preparing paste of standard consistency) to the dry mix of cement and sand and mix thoroughly for a minimum of 3 minutes and maximum of 4 minutes to obtain a mix of uniform colour. If even in 4 minutes uniform colour of the mix is not obtained reject the mix and mix fresh quantities of cement, sand and water to obtain a mix of uniform colour.
3. Place the thoroughly cleaned and oiled (on interior face) mould on the vibrating machine and hold it in position by clamps provided on the machine for the purpose.
4. Fill the mould with entire quantity of mortar using a suitable hopper attached to the top of the mould for facility of filling and vibrate it for 2 minutes at a specified speed of 12000±400 per minute to achieve full compaction.
5. Remove the mould from the machine and keep it in a place with temp of 27±2⁰C and relative humidity of 90% for 24 hours.
6. At the end of 24 hrs remove the cube from the mould and immediately submerge in fresh clean water. The cube be taken out of the water only at the time of testing.
7. Prepare at least 6 cubes in the manner explained above.
8. Place the test cube on the platform of a compressive testing machine without any packing between the cube and the plates of the testing machine.
9. Apply the load steadily and uniformly, starting from zero at a rate of 35 N/mm²/minute.

Calculation

Where,

P=Maximum load applied to the cube. (N)

A=Cross sectional area (Calculated from the mean dimensions) (mm²)

• Compressive strength is reported to the nearest 0.5 N/mm².
• Specimens that are manifestly faulty, or that give strengths differing by more than 10% from the average value of all the test specimen should not be considered.
• Test three cubes for compressive strength for each period of curing.

Precautions

• The mould should be oiled before use
• The weighing should be done accurately
• The temperature and humidity must be accurately controlled
• Increase the load gradually during testing.
• The cubes should be tested immediately after taking out of water and not allowed to dry until they fail under testing.
• The gauging time should be strictly observed.
• The cubes should be tested on their sides and not on their faces.

Standard Specifications

CEMENT TYPE	COMPRESSIVE STRENGTH (Mpa)
	1 Day	3 Days	7 Days	28 Days
OPC(33)	—	16	22	33
OPC(43)	—	23	33	43
OPC(53)	—	27	27	53
SRC	—	10	16	33
PPC	—	16	22	33
RHPC	16	27	—	—
PSC		16	22	33
High alumina	30	35	—	—
Super sulphated	—	15	22	30
Low heat	—	10	16	35
Masonry	—	—	2.5	5.0
IRS-T-40	—	—	37.5	—

Technical Discussions

• Strength tests are not made on a neat cement paste because of difficulties of moulding and testing with a consequent large variability of test results.
• Compressive strength is influenced by the cement type, or more precisely, the compound composition and fineness of cement.
• It should be assumed that two types of cement meeting the same minimum requirements will produce the same strength of mortar or concrete without modification of mix proportions.