Method of concrete compression test with 150mmx150mmx150mm cube samples

In concrete compression test, usually 150mmx150mmx150mm concrete cube samples are arranged for performing test. Can 100mmx100mmx100mm concrete cube samples be applied in the test in place of 150mmx150mmx150mm concrete cube samples?

Fundamentally, the force delivered by a concrete compression machine belongs to a definite value. When normal concrete strength is used i.e. under 50MPa, the stress delivered by a 150mmx150mmx150mm cube is adequate for the machine to crush the concrete sample.

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

So,100mmx100mmx100mm concrete cubes can be utilized in place of 150mmx150mmx150mm cubes to raise the applied stress to crush the concrete cubes. For normal concrete strength, the cube size of 150mmx150mmx150mm is already adequate for the crushing strength of the machine.

Cube Test:

Tools and Materials: Concrete cube mould with size 150mm or 100mm. It is utilized for aggregate size not surpassing 40mm and 25mm. Cube mould for test should be done from steel or cast iron having smooth inside surface. Every mould should contain steel plate to support and to resist leakage.

Compacting steel rod having 16mm diameter and 600mm length.

Compression test machine:

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

Fill the cube with concrete in three layers.

Each layer should be consolidated for 25 times. This method is performed systematically and compaction is performed consistently to all the surfaces of the concrete. Compaction can also be performed with machine.

The surface of concrete should be flattened to maintain the identical level with the upper side of the mould. The cubes produced at construction site should be covered with plastic cover for a period of 24 hours prior to disassemble the moulds.

Once remoulded is completed, the concrete cubes are drowned in water for curing.

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

Result: Record the Strength value of each cube and compare with the targeted strength value. The objective of conducting the concrete test on 7 th day and the 14 th day is to forecast whether the concrete could attain the targeted 28 th day strength. Normally, the concrete would have obtained 70% strength on the 7 th day.

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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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Some vital steps for concrete post-pour inspection

This civil engineering article sheds light on the required steps for post-concrete inspection as soon as decluttering of any concrete structure is completed.

The activities prior to arrange concrete comprise of utilization and maintenance of curing compound or other techniques of curing, form removal, concrete repair and preservation of concrete cubes. The subcontractor will inform QA/QC that curing is retained by the submittal of curing records.

Some vital Inspection points:

Given below, the details about major key inspection items to be examined and/or checked in the context of concrete post placement activities:

• Ensure that the necessary method of curing is prepared.
• Ensure that the placement is examined constantly to assure uninterrupted curing (watch for dry spots).
• Ensure that curing is retained for a prolonged time if necessary.
• Ensure that proper protection against bad weather is taken when necessary (hot or cold weather) as indicated in specifications.
• Ensure that concrete forms are departed in exact position for prolonged time to assure that form removal will keep concrete undamaged or workers (take precautions concerning the forms supporting the weight of the concrete to make sure the concrete has attained adequate strength to sustain its own weight)
• When repair of concrete is essential, check that it is repaired compliant with specifications (on the basis of the intensity of the repair, verify if a nonconformance report is necessary)
• Ensure that concrete cylinders are preserved on site in conformity with BS codes and job site requirements
• Ensure that concrete cylinders are transported to the testing laboratory and consequently tested compliant with BS and job site requirements Documentation

The Concrete Pour Card (Attached at the end) and Concrete Test Report as well as all supporting documents associated with the concrete pour should be arranged in the master file for the specific concrete pour. These files should be retained during the construction process and prepared in compliance with the methods of Control of Quality Records. There should be a proper labeling system for the project that sustains traceability among the concrete test report and the Concrete Pour Card.



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Published By
Rajib Dey
www.constructioncost.co
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