Determining the number of concrete cubes to cast is a crucial aspect of conducting the compressive strength test, which is a significant test performed on concrete to assess its quality. Site engineers often grapple with the question of how many samples to cast during the test. To address this query, it is essential to refer to the guidelines provided by the Indian standard code IS 456.
In this article, we will delve into the process of determining the number of samples to cast according to IS 456. The article will also provide examples to help readers understand the procedure better. By following the guidelines provided in IS 456, site engineers can ensure that they obtain accurate and reliable test results.
Concrete Cubes Sampling
The minimum frequency of sampling of concrete of each grade shall be in accordance with the following:
Note:
The table provided specifies the number of samples required for a 28-day compressive strength compliance requirement. However, it is important to note that additional samples must be cast to determine the strength at 7 days or at the time of striking the formwork, as directed by the engineer-in-charge. This means that while the table provides guidance for the minimum number of samples required, it may be necessary to cast more samples in order to accurately assess the compressive strength of the material being tested. By following the instructions of the engineer-in-charge, the testing process can be tailored to the specific needs of the project, ensuring that accurate results are obtained and the strength of the material is properly assessed.
Example 1:
For a quantity of 14 m3 of concrete, the prescribed number of samples as per the given table is 2 samples or 6 cubes. These samples are to be cast from each batch of 7 m3, for 28-day testing. Additionally, another 1 sample or 3 cubes shall be cast for 7-day testing. This testing process is important to ensure that the concrete meets the necessary quality standards and can perform as intended. By casting these samples and conducting tests at different intervals, any potential issues or defects in the concrete can be identified and addressed early on, ensuring the safety and reliability of the final structure.
Example 2:
According to the table provided, for 220 cubic meters of concrete, a total of eight samples need to be taken. This includes four samples for concrete up to 50 cubic meters, and one sample each for concrete within the ranges of 50-100 cubic meters, 100-150 cubic meters, 150-200 cubic meters, and 200-220 cubic meters. For each batch, 32 cubes need to be cast for 28-day testing, and an additional six cubes need to be cast for 7-day testing as per the instructions of the engineer in-charge. To ensure the quality of the concrete construction, it is important to perform cube tests to determine the compressive strength of the concrete. This involves casting cubes from the concrete batches and testing them after 7 and 28 days to determine their strength. It is also recommended to calculate the standard deviation of the compressive strength to ensure that the concrete meets the required quality standards.