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**What is Compressive Strength of Cement Mortar?**

The

**compressive strength of cement mortar**or concrete is one of the most important and useful property. The compressive strength test is done on cement, when it is used as cement mortar and concrete.
Compressive
strength of cement is determined by

**compressive strength test**on cement mortar cubes compacted by means of a standard vibration machine. Standard sand (as per IS: 650) is used for the preparation of cement mortar cubes.
The measured compressive
strength of the cubes is calculated by dividing the maximum load applied to the
mortar cubes during the test by the cross-sectional area, calculated from the
mean dimensions of the section.

The average compressive strength of at least
three cement mortars cubes (area of the face 50 cm²) composed of one part of
cement and the other three parts of standard stand should satisfy IS code
specifications

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**Compressive Strength of Cement Mortar Lab Report, IS: 4031 (Part 6) – 1988**

Hi friends, you are welcomed in the world of Civil
Allied Gyan. Here I have explained about the
determination of the compressive strength of hydraulic cement mortars
cubes. "Read definition, apparatus, IS code, test
procedure, formula, result, lab report and significance about

**compressive strength of cement mortar**."- IS: 4031 (Part 6) – 1988

**Apparatus Required for Compressive Strength Test of Cement Mortars**

**:-**

- Standard sand as per IS: 650-1966
- Compression Testing Machine
- Vibration machine
- Poking rod
- Cube mould size conforming to IS: 10080-1982
- Weighing balance
- Trowel
- Stopwatch
- Dial gauge
- Graduated glass cylinders of 150 to 200 ml capacity with ± 1 ml variation

**Temperature and Humidity:-**

Ã˜ The temperature
of moulding room, dry materials and water will be maintained at 25 °C to 29 °C. The relative humidity of the laboratory will be 60 to
70 percent.

Ã˜ The moist
closet or moist room will be maintained at 25 °C to
29 °C and at a
relative humidity of not less than 90 percent.

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**Procedure for Compressive Strength of Cement Mortars Test****:-**

**Preparation of test specimens:-**Clean appliances will be used for mixing and the temperature of water and that of the test room at the time when the above operations are being performed will be 25 °C to 29 °C. Distilled water will be used in preparing the cubes.- The material for every cube will be mixed separately and the quantity of cement, standard sand and water are going to be as follows: cement 200g, standard sand 600g and water (p/4+0.3) percent of combined mass of cement and sand, where p is the percentage of water required to produce a paste of standard (or normal) consistency.
- Then place a mixture of cement and standard sand on a nonporous plate.
- First, mix it dry with a trowel for one minute and then with water until the mixture is going to be as of uniform colour. The quantity of water to be used will be as specified in step 2.
- The time of mixing will in any event be not less than 3 minutes and if the time taken to obtain a uniform colour exceeds to 4 minutes, the mixture will be rejected and the whole operation will be repeated with a fresh quantity of cement, sand and water.
**Moulding specimens:-**In assembling the moulds ready for use, treat the interior faces of the mould with a thin coating of mould oil.- Place the assembled mould on the table of the vibration machine and hold it firmly in position by means of an appropriate clamp. Attach a hopper of suitable shape and size securely at the top of the mould to facilitate filling and this hopper will not be removed until the completion of the vibration period.
- Immediately after mixing the mortar in accordance with step 1 & 2, place the mortar within the cube mould and prod with the rod. Place the mortar in the hopper of the cube mould and prod again as specified for the first layer and then compact the mortar by vibration machine.
- The period of vibration will be two minutes at the specified speed of (12000 ± 400) vibrations per minute.
- At the end of vibration, remove the mould together with the base plate from the machine and finish the top surface of the cube in the mould by smoothing the surface with the blade of a trowel.
**Curing specimens:-**Keep the filled moulds in moist closet or moist room for 23 to 25 hours after completion of vibration. At the end of that period, remove them from the moulds and immediately submerge in cleaned fresh water and keep there until taken out just before breaking.- The water in which the cubes are submerged will be renewed every 7 days and will be maintained at a temperature of 25 °C to 29 °C. After they have been taken out and until they are broken, the cubes will not be allowed to become dry.
- Test three cubes for
**compressive strength**for each period of curing mentioned under the relevant specifications (i.e. 3 days, 7 days and 28 days) for different hydraulic cements, the periods being reckoned from the completion of vibration. - The cubes will be tested on their sides without any packing between the cube and the steel platens of the testing machine. One of the platens will be carried on a base and will be self-adjusting, and the load will be steadily and uniformly applied, starting from zero at a rate of 35 N/mm²/min.

**Observations:-**

Type of cement
= ........................

Brand of cement
= ........................

Date of casting
= ..........................

**Table:-**

**Calculations:-**

**Result:-**

The average compressive strength of the given
cement mortar cubes are

1) 3 days ………………………. N/mm²

2) 7 days……………………….. N/mm²

3) 28 days……………………… N/mm²

**Report:-**

The average values of compressive strength (3 days, 7
days and 28 days) of the three mortar cubes is reported to the nearest 0.5 N/mm

^{2}.
Ã˜ 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.

Ã˜ After discarding specimens or strength values, if less than
two strength values are left for determining the

**compressive strength**at any given period, a retest will be made.**Safety and Precautions While Testing:**

- Clean the apparatus thoroughly before testing and after testing.
- The test should be performed away from vibrations and other disturbances.
- Wear helmet, shoes and hand gloves during the test.
- The moulds should be oiled before the experiment.
- The weighing should be done accurately.
- The temperature and humidity must be accurately controlled.
- Increase the load gradually during testing.
- The cement mortar 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.

- The compressive strength of cement mortar cubes or concrete is one of the most important and useful property.
- The
**compressive strength of cement mortars**is determined in order to verify whether the cement conforms to Indian Standard (IS, or other standards like ASTM, BS etc.) specifications and whether it will be able to develop the concrete of required compressive strength. - The compressive strength test is done on cement, when it is used as cement mortar and concrete.
- As a construction material, concrete is employed to resist the compressive stresses. While, at locations where tensile-strength or shear-strength is of primary importance, the compressive strength is used to estimate the required property of cement mortar cubes.
- The mixture of cement and sand in water is generally weak in tension but it is strong in compression when it is subjected to tensile tension with iron rods. The mortar is used for plastering and brick masonry. The first case gives mortar heavy load in form of construction on it by placing bricks on mortar .that is why, it is important to know the strength of the mortar.
- The strength of the binder (cement) therefore has a significant effect on the performance characteristics of the mixture of cement and sand and ensures the overall quality of the finished product.

The mixture of cement and sand are in pre-defined ratios
and the compressive strength of the mortar depend on the quality of the cement,
the gradation of sand used in mixture and the water–cement ratio.

The

**compressive strength of cement mortar**depends on the strength and weakness of the mortar cube. If mortar cube is weak then the compressive strength of the mortar cube is also weak. If mortar cube is strong, then the compressive strength of the mortar cube will be high.
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