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Ready Mixed Concrete Casting and Experiments

23.08.2022
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Ready Mixed Concrete Casting and Experiments

Quality Control

The quality of fresh concrete is determined by sampling. It is assumed that these samples are the exact sample of the concrete poured at the construction site and represent its quality.

Sample Collection

1. Each sample should be taken from a separate batch or separate truck mixer.

2. The sample should be taken at the site delivery site after the first 15% of the concrete discharged from the truck mixer trough and before the last 15%.

3. The sample to be taken from the truck mixer trough must represent the whole flowing concrete, not any part.

4. The date and time of sampling should be recorded. If necessary, the temperature of the fresh concrete and the ambient temperature should also be recorded.

Sample Preparation

1. At every stage of sampling and transport of samples, concrete must be protected against contamination, water absorption, water loss and temperature changes.

2. Concrete samples are filled into the molds in equal layers, the height of which does not exceed 10 cm. 15 cm. or 20 cm cubes should be filled in two layers and 15/30 cm cylinders in three layers.

3. The strokes of the clamping bar are evenly distributed over the die cross-sectional area. Care should be taken that the bar does not hit the mold base hard when compacting the first poured layer, and that it does not penetrate the previous layer too much during the compression of the other layers.

4. Each layer should be skewered at least 25 times with the compression rod. After compression, the outer edges of the mold should be tapped lightly with the mallet until the gaps remaining from the compression rod impacts are filled.

5. Excess concrete overflowing from the upper surface of the mold should be removed by making a cutting action with a steel trowel or finishing trowel and the concrete surface should be carefully smoothed.

6. Specimens must be visibly and permanently labeled without damage. Sample records (day and time taken, concrete strength class, site code, facility name, transmixer plate, delivery note number) should be kept meticulously.

Storage and Transport of Samples on Site

1. The samples are protected from external effects, shock, vibration and drying until they reach sufficient hardness in the mold (not less than 16 hours, not more than 3 days) without being transported from the place where they were taken.

2. The samples are kept in an environment (under a wet cloth and plastic cover or in a closed case) at a temperature of 20±2 °C or 25±2 °C in hot climates, protected from wind and moisture loss.

3. Samples should be prevented from being affected by excessive temperature changes and moisture loss during transportation.

4. Hardened test specimens can be stored in wet sand or wet sawdust or placed in a sealed plastic mold containing water.

Curing of Samples

1. Concrete samples, after being removed from the mold, should cure in water at a temperature of 20±2 °C (or in a 95% humidity environment) until the test is performed.

There are two situations for taking samples from concrete produced according to TS EN 206-1 standard. Initial production includes production until at least 35 test results are obtained. Continuous manufacturing is the manufacturing after at least 35 test results have been obtained in a period of not more than 12 months.

For the minimum sampling and testing frequency of concrete, the frequency that gives the maximum number of samples in initial and continuous production should be selected in Table 1. Samples should be taken after adding water or chemical additive to the concrete under the responsibility of the manufacturer in accordance with the sampling conditions. However, if it has been determined by initial tests that the amount of plasticizer or superplasticizer to be used does not have a negative effect on the concrete strength, sampling may be allowed before such additives are added to adjust the consistency.

If the difference between the largest and smallest test results obtained from two or more samples prepared from the same fresh concrete sample is more than 15% deviation from the average result, except if an acceptable reason is found for discarding any of the test results as a result of the examination, test results are rejected.

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