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The compressive strength test is one of the most important tests performed on concrete. This test gives a fair idea about the quality of the concrete that is being poured at the site. While conducting this test, the major question that emerges in front of a site engineer is - How many Concrete Cubes to Cast?
In this article, we will discuss how to determine the number of samples to cast as per IS 456 with examples.
Concrete Cubes Sampling
The minimum frequency of sampling of concrete of each grade shall be in accordance with the following:
The number of samples mentioned in the table is for a 28 days compressive strength compliance requirement. Additional samples shall be cast to determine the strength of 7 days or at the time of striking the formwork as per the instruction of the engineer-in-charge.
Quantity of Concrete: 14 m3
The prescribed number of samples for 14 m3 of concrete as per the above table is 2 samples (6 cubes)
Therefore, 2 samples (6 cubes) from each batch of 7 m3 shall be cast for 28-day testing and an additional 1 sample (3 cubes) shall be cast for 7-day testing.
Quantity of Concrete: 220 m3
The prescribed number of samples for 220 m3 of concrete as per the above table shall be:
= 4 + 1 + 1 + 1 + 1 Samples
= 8 Samples
(4 samples up to 50 m3, 1 sample for 50 - 100 m3, 1 sample for 100 - 150 m3, 1 sample for 150 - 200 m3 and 1 sample for 200 - 220 m3)
Therefore, 8 samples (32 cubes) from each batch shall be cast for 28-day testing and an additional 2 samples (6 cubes) shall be cast for 7-day testing as per the engineer in-charge.
Compressive Strength of Concrete -Cube Test [PDF], Procedure, Results
Standard Deviation for Compressive Strength of Concrete with Example [PDF]