Quality Control, Testing, and Inspection
What the exam tests
Quality control, testing, and inspection tests inspection and test plans, hold and witness points, sampling, acceptance criteria, and non-conformance handling. Expect concrete, compaction, and calibration scenarios.
Core rules and concepts
- An inspection and test plan (ITP) lists activities, the inspection or test, the acceptance criterion, and whether the point is hold (work stops) or witness (notification only).
- Samples must be random and representative, taken at the specified frequency, and handled without damage or moisture loss.
- Concrete cubes are normally tested at 28 days; 7-day results indicate early strength but do not replace the 28-day acceptance decision.
- Acceptance compares results with the specification; for concrete, criteria commonly require the mean of a group to exceed the characteristic strength by a margin and every individual result to stay above a lower limit.
- Equipment must be calibrated and traceable; an uncalibrated test is not evidence.
- A non-conformance report records the deviation, disposition, and corrective action.
Worked example
Three 28-day cubes give 31, 33, and 29 MPa against class C25/30. Mean = 93/3 = 31 MPa, minimum = 29 MPa. Using the common criteria mean ≥ fck + 4 = 29 MPa and individual ≥ fck − 4 = 21 MPa, the group passes both. The reasoning uses the specified characteristic strength of 25 MPa and the project specification criteria; always confirm which criterion the specification adopts rather than assuming.
Traps that cost marks
- Treating a 7-day result as final acceptance.
- Testing with out-of-calibration equipment.
- Taking convenience samples rather than random ones.
- Ignoring a hold point and proceeding with the next activity.
- Closing a non-conformance without recorded corrective action.