Design Mix Concrete Acceptance Criteria:
The strength requirements of concrete can be met in two ways. Firstly, if every sample has a test strength that is equal to or greater than the characteristic value. Alternatively, the strength of one or more samples may be lower than the characteristic value, but still meet the requirements if certain conditions are met.
In the latter case, the strength of each sample that is lower than the characteristic value must still be greater than either the characteristic strength minus 1.35 times the standard deviation, or 0.80 times the characteristic strength. Additionally, the average strength of all the samples must be equal to or greater than the characteristic strength plus a certain multiple of the standard deviation.
If either of these conditions are not met, then the concrete will not be deemed to comply with the strength requirements. It is important to ensure that the concrete meets these standards to ensure its structural integrity and safety.
The strength requirements for concrete state that the concrete will not be considered compliant if certain conditions are met. The first condition is that if the strength of any sample is less than the greater of two values, then the concrete will not meet the strength requirements. The first value is calculated by multiplying the characteristic strength of the concrete mix by 1.35 times the standard deviation. The second value is calculated by multiplying the characteristic strength of the concrete mix by 0.80. If either of these values is greater than the strength of any sample, then the concrete will not meet the strength requirements.
The second condition that will cause the concrete to be deemed non-compliant is if the average strength of all samples is less than the characteristic strength plus a certain value times the standard deviation. The specific value that must be added to the characteristic strength depends on the testing protocol being used. If this average strength is less than the required value, then the concrete will not meet the strength requirements.
Paragraph I specifies the minimum required strength for concrete. Paragraph II outlines the maximum allowable water-cement ratio for different classes of concrete. Concrete that doesn’t meet the strength requirement specified in Paragraph I but still has greater strength than that required in Paragraph II may be accepted by the designer without further testing, as per Paragraph III. Each grade of concrete shall be assessed separately, according to Paragraph IV. Compliance checks of concrete shall be conducted daily, as stated in Paragraph V. If concrete is found to be porous or honeycombed, or if it has not been placed properly, or if construction tolerances are not met, it may be rejected, as per Paragraph VI. However, the hardened concrete may be accepted after remedial measures have been carried out to the satisfaction of the relevant parties. Finally, as per Paragraph VIII, concrete that has an average strength value less than a specified amount after a certain number of tests shall be rejected.
