**Compressive strength of cement at 7 days & 28 days,** hi guys in this article we know about compressive strength of **OPC, PPC, PSC, SRC, RHPC, HAC, SSC,IRS-T 40 & RHC** cement and cement mortar by making cube test pressing with hydraulic machine and also know about compressive strength test of cement.

**Compressive strength of cement** is determined by cube test on cement mortar cubes compacted by means of a standard vibration hydraulic machine. Standard vibration for making cube is 12000 +- 400 vibration per minute and it will vibrate for 2 minute.

**Standard sand according to IS:650** is known as innor sand obtained from Tamil Nadu used for the preparation of cement mortar. For the preparation of cement mortar we use cement sand ratio is 1:3 in which one part is cement and 3 part is sand.

Make a small size of 3 cube having specimen (l × b × h) 70.6mm×70.6mm×70.6mm. Large Size of cube is not made because of shrinkage and cracking.

**Compressive strength of cement at 3,7 & 28 days.**

Cement compressive strength is calculated in SI unit MPa which is equal to N/mm2 and in us customary region, it is measured in pound force per square inch commonly represented as psi.

There are different types of cement like **OPC, PPC, PSC, SRC, RHPC, HAC, SSC,IRS-T 40 & RHC** cement. Let us discuss about different types of cement and their compressive strength.

For masonry cement, compressive strength is ranging between 33 – 53MPa at 28 days, 22- 27 MPa at 7days and 16 -27MPa at 3days of curing after casting.

**Compressive strength of ordinary Portland cement (OPC)- **OPC stand for ordinary Portland cement represented as OPC33, OPC43 & OPC53. Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th century by Joseph Aspdin, and usually originates from limestone.

For ordinary Portland cement (OPC), compressive strength is ranging between 33 – 53MPa at 28 days, 22- 27 MPa at 7days and 16 -27MPa at 3days of curing after casting.

**● Compressive strength of Portland Pozzolana cement (PPC):** PPC stand for Portland Pozzolana cement. Pozzolana cement (PPC) is manufactured by combination of pozzolanic materials. Pozzolana is an artificial or natural material which has silica in it in a reactive form

For Portland Pozzolana cement (PPC), compressive strength is 33MPa at 28 days,22MPa at 7days and 16MPa at 3days of curing after casting.

**● Compressive strength of Portland slag cement (PSC):** PSC stand for Portland slag cement. Portland Slag Cement (PSC) is manufactured by either inter-grinding in the Portland cement clinker, Gypsum & Granulated Slag or blending the Ground Granulated Blast Furnace Slag (GGBS) with Ordinary Portland Cement by means of mechanical blenders.

For Portland slag cement(PSC), compressive strength is 33MPa at 28 days, 22MPa at 7days and 16MPa at 3days of curing after casting.

**● Compressive strength of sulphate resisting Portland cement (SRC):** SRC stand for Sulphate Resisting Portland Cement,it is a type of Portland cement in which the amount of Tricalcium aluminate (C3A) is restricted to lower than 5 % and (2 C3A + C4AF) is lower than 25%. SRC can be used for structural concrete.

For sulphate resisting portland cement (SRC) compressive strength is 33MPa at 28 days, 16MPa at 7days and 10MPa at 3days of curing after casting.

**● Compressive strength of rapid hardening Portland cement (RHPC):** Rapid Hardening Portland Cement is the cement with higher Clinker content of Tri Calcium Silicate(C3S). It is finer in grinding and has rapid hardening properties however the final strength is equal to that of Ordinary Portland Cement.

For rapid hardening portland cement (RHPC), compressive strength is 27MPa at 3 days and 16MPa at 1days of curing after casting.

The one day strength of RHC is comparable with three day strength of OPC

**● Compressive strength of Low Heat Portland Cement:** it is the cement with high Di Calcium Silicate contents (C2S) and lower C3A and C3A contents .The rate of evolution of heat is slower initially but in later stages both setting and hardening rates are faster than OPC.

For low heat portland cement, compressive strength is 35MPa at 28 days, 16MPa at 7days and 10MPa at 3days of curing after casting.

**● Compressive strength of High Alumina Cement (HAC):** sometimes it is known as calcium aluminate cement (CAC) or aluminous cement, is composed of calcium aluminates, unlike Portland cement which is composed of calcium silicates. It is manufactured from limestone or chalk and bauxite

For high alumina cement (HAC), compressive strength is 35MPa at 3 days and 30MPa at 1days of curing after casting.

**● Compressive strength of Super Sulphated cement (SSC):** It is made from well granulated blast furnace slag (80- 85%), calcium sulphate(10- 15%), and Portland cement (1 – 2 %) and is ground finger than the Portland cement. One of its most important properties is its low total heat of hydration.

For super sulphated cement (SSC), compressive strength is 30MPa at 28 days, 22MPa at 7days and 15MPa at 3days of curing after casting

**● Compressive strength of IRS-T 40 Cement:** It is a special type of cement which is mainly used in railway works only. This special cement is manufactured under the specifications that are approved by the ministry of Indian Railways. This cement contains high volume of C3S content which are finely grinded inorder to develop high early strength.

For high IRS-T 40 Cement, compressive strength is 37.5MPa at 7 days of curing after casting.

**Compressive strength test of cement**

Compressive strength of cement is determined by cube test on cement mortar cubes compacted by means of a standard vibration hydraulic machine. Standard vibration for making cube is 12000 +- 400 vibration per minute and it will vibrate for 2 minute.

**1) For the cube test we require following appartus**

● Cube mould size 70.6 ×70.6×70.6 mm3(IS:10080)

● Vibration machine Should be as per IS:10080

● Balance 1000 g

● Measuring cylinder 200 ml

● and other apparatus is used for cube test is

Enamel tray, Trowel, Poking rod,Cement Mould

**2) environmental condition:** the temperature should be 29℃ or 25℃ are represented as temperature 27 ± 2°C, humidity should be 65 ± 5%

**3) cement sand ratio:**_ cement sand ratio for preparing mortar is 1:3 in which one part is cement and 3 part is sand.

**Procedure for compressive strength Test of cement**

Take 200 g of cement and 600 g of standard sand (1:3) and mix them dry thoroughly.

Add cement consistency is 2 for 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 2 minutes by vibrator at the rate of 12000+- 400 per minute to obtain a mix of uniform colour.

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.

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.

Remove the mould from the machine and keep it in a place with temp of 27±2°C and relative humidity of 90% for 24 hours.

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.

Prepare at least 3 cubes in the manner.

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.

Apply the load steadily and uniformly, starting from zero at a rate of 35 N/mm2/minute.

Cement compressive = load/ cross sectional area F= p/A

Where, F = cement compressive strength

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

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

**● PRECAUTIONS:-**

1)The mould should be oiled before use

2)The weighing should be done accurately

3)The temperature and humidity must be accurately controlled

4) Increase the load gradually during testing.

5) The cubes should be tested immediately after taking out of water and not allowed to dry until they fail under testing.

6) The gauging time should be strictly observed.

7) The cubes should be tested on their sides and not on their faces.

**● Technical discussion:-**

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.

● **Time and strength gain: time and strength of cement relationship are non linear.**

1) 1 day of curing time cement gain its strength about 16% of total strength

2) 3 days of curing time cement gain its strength about 40% of total strength

3) 7 days of curing time cement gain its strength about 65% of total strength

4) 14 days of curing time cement gain its strength about 90% of total strength

5) 28 days of curing time cement gain its strength about 99% of total strength

6) 3 months of time cement gain its strength about 110% of total strength

7) 6 months of time cement gain its strength about 115% of total strength

8) 1 year of time cement gain its strength about 120% of total strength.

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