According to ASTM C172, what is the minimum number of locations within a concrete batch from which samples must be taken to ensure a representative sample?

According to ASTM C172, Standard Practice for Sampling Freshly Mixed Concrete, samples must be taken from at least two different portions of the concrete batch to ensure a representative sample. These portions should be obtained from the middle of the batch. The practice specifies that these portions should be combined into one composite sample for testing. Taking samples from multiple locations helps to account for any variations in the concrete mix within the batch, ensuring that the sample used for testing accurately represents the overall characteristics of the concrete being produced. If the concrete is being discharged from a stationary mixer, the portions should be taken at approximately the quarter and three-quarter points of the batch discharge. For a paving mixer, the portions should be taken from different areas of the discharged pile. This ensures that the sample is not biased towards any particular part of the batch that might be unrepresentative of the whole.