Sufficient Sampling to Determine the Cover Depth of Reinforcement and Carbonation Depth for In-use and Reclaimed Concrete Elements

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Abstract
This study addresses how many samples are sufficient to reliably estimate the cover depth of reinforcement and the carbonation depth of indoor load-bearing concrete elements. A Monte Carlo simulation with 10,000 iterations for extreme values of real cases was used to evaluate the standard error of the mean for different numbers of samples. To evaluate the cover depth of reinforcement, the simulation results suggest that 150 measurements are statistically sufficient for a certain reinforcement type and for each element type. However, hollow-core slabs can be treated as a distinct population due to their consistently low variability in cover depth. Reliable preliminary estimate can be obtained with only 10 measurements, while 30 measurements are sufficient to achieve high statistical reliability. To estimate the carbonation depth, 12-14 samples are recommended. The carbonation depth varies between elements and among samples, so the utmost care should be taken when determining sampling spot and the value for an individual sample.

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