What is one method of Quality Assurance testing?

Retesting 10% of quality control core samples is a valid method of Quality Assurance testing because it provides an additional layer of verification to ensure the accuracy and reliability of the initial testing. By retesting a portion of the samples, the process helps to confirm that the original quality control measures were effective and that the materials used in the construction or repair meet the established standards. This approach can help detect any potential errors in the initial tests and reinforce confidence in the overall quality of the work performed.

In the context of the other options, conducting verification sampling at a frequency of 5% may not provide a sufficient overview of the quality if the samples are not representative. Using fixed sampling locations can limit the ability to assess variability across the entire project site, potentially missing critical quality issues that may arise in other areas. Involving only contractor personnel risks introducing bias into the testing process, as external oversight or independent verification is often crucial for maintaining objectivity and integrity in Quality Assurance practices.