Some vital tests to check the quality of concrete

Concrete is mainly a composite material that comprises of fine & coarse aggregate, water, cement, and admixtures.

To obtain high-quality concrete, the sample should be examined thoroughly to ensure whether it is formed according to requirement or not. If the test for concrete is not conducted, the following problems will occur :-

• Cracks and voids in the finished concrete.
• The concrete of Low compressive strength.
• Bleeding

Given below, the details on some vital tests of concrete:

1. Workability test
2. compressive strength test
3. Non-destructive test
4. Destructive test
5. Durability test

WORKABILITY TEST: Workability test plays a crucial role since it is associated with the strength of concrete. Workability means the capacity to fill the mould perfectly with the vibrator but the quality of concrete is not affected. The Workability of concrete is calculated with the following test:

• SLUMP TEST
• VEE-BEE TEST
• COMPACTING FACTOR TEST

Compressive strength of concrete: The concrete can’t sustain the compressive load. So, it becomes essential that any concrete member could withstand a good amount of compressive load.

Under this test, the maximum compressive strength of the concrete sample is ascertained after 28 days of curing. Based on the standard code of India, 150 mm concrete cubes are utilized in this test. Under this test, the concrete sample should be immersed for 28 days and after each 7 days water should be changed. After 28 days of curing, the concrete specimen is arranged on the machine plate.

Now load is provided slowly to the specimen unless the collapsing of the concrete cube occurs. Destructive and Non-destructive Test of Concrete These tests are carried out to find out the compressive strength of the existing concrete structure where the required concrete sample is not available.

This types of tests are conducted with the destructive or Non-destructive way.

If Non- destructive way is followed, compressive strength should be established devoid of affecting the structure or any concrete member. The Non-destructive test is conducted on the following ways :

• Rebound hammer test
• Penetration and pullout techniques
• Surface hardness test
• Radio-active method

Most common Destructive tests are as follows:

• Concrete core test
• Cube test
• Tensile strength test

Durability Test: With the purpose of maintaining the sustainability of concrete, the stability of concrete is required. To enhance the stability of concrete, it's vital that concrete should contain the following qualities :

• Water resistance
• Chloride attack resistance
• Resistance to infiltration of water.

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Published By
Rajib Dey
www.constructioncost.co
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Methods of concrete cube test

In concrete compression test, generally the concrete cube samples with dimensions 150mmx150mmx150mm are utilized. But, in place of 150mmx150mmx150mm concrete cube samples, 100mmx100mmx100mm concrete cube samples are applied for the test.

Fundamentally, the force produced through a concrete compression machine is a definite value. For the use of normal concrete strength, suppose under 50MPa, the stress provided by a 150mmx150mmx150mm cube is adequate for the machine to smash the concrete sample.

However, when the intended concrete strength is 100MPa, under the equivalent force (about2,000kN) delivered by the machine, the stress under a 150mmx150mmx150mm cube is inadequate to crush the concrete cube.

So, 100mmx100mmx100mm concrete cubes are used in place of 150mmx150mmx150mm cubes to raise the used stress to crush the concrete cubes. For normal concrete strength, the cube size of 150mmx150mmx150mm is already sufficient for the crushing strength of the machine.

Cube Test:

Instrument And Material.

Concrete cube mould with size 150mm or 100mm is applied for aggregate size of not more than 40mm and 25mm. Cube mould for test should be formed into steel or cast iron containing smooth inner surface. Each mould should contain steel plate to support and avoid leakage.

Compacting steel rod should be used with 16mm diameter and 600mm length.

The test should be conducted by compression test machine.

Method: Mould and base plate should be cleansed and employed with oil so that the concrete can’t fix to the side of the cube. Base plate is affixed to the mould with bolt and nut.

The cube should be filled with concrete in three layers.

Each layer should be consolidated for 25 times. This process should be accomplished systematically and compaction should be finished equally to all the surfaces of the concrete. Compaction is also done with machine.

The surface of concrete should be leveled to retain the equivalent level with the upper side of the mould.

Cubes which are produced at construction site should be wrapped with plastic cover for a period of 24 hours prior to remove the moulds.

After remoulded, the concrete cubes should be drowned in water for curing.

Compression strength test should be conducted for concrete at age 7, 14, and 28 days through compression test machine.

Result: The Strength value of each cube should be noted and compared with the targeted strength value. The reason for conducting the concrete test on 7 th day and the 14 th day is to anticipate whether the concrete could attain the targeted 28 th day strength. Normally, concrete can obtain 70% strength on the 7 th day.

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Published By

Rajib Dey

www.constructioncost.co

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