Inspection and Testing of Fresh and Hardened Concrete
What this domain tests
This domain tests sampling, fresh concrete tests, specimen handling, and acceptance decisions. Questions often present test results and ask whether the lot conforms and what action follows.
Core rules
- Fresh tests commonly include slump by ASTM C143, air content by C231 or C173, temperature by C1064, and unit weight by C138. Use the method appropriate to the aggregate type.
- Strength specimens follow ASTM C31 for making and curing and C39 for compression testing. Initial curing must protect cylinders from moisture loss and temperature extremes.
- Sample at the required frequency and from the required location. Record mix identification, time, location, and specimen identity.
- Acceptance criteria come from the project specification. Under common ACI 318 rules, the average of three consecutive strength tests must equal or exceed f-prime-c, and no individual test may fall below the stated lower limit.
- Failed tests trigger investigation, not automatic rejection: check sampling, curing, testing, and product history before disposition.
Worked example
A 6,000 psi mixture returns three consecutive strength tests of 5,900, 6,100, and 5,700 psi. The average is 5,900 psi, below 6,000 psi, so the average criterion fails. The lower individual limit for f-prime-c above 5,000 psi is 0.90 x 6,000 = 5,400 psi; 5,700 psi passes that check. Because the average fails, the plant investigates batch records, cylinder curing, and test machine calibration, then obtains project acceptance disposition.
Traps
Using the wrong air-meter method; testing unrepresentative samples; letting cylinders dry or freeze; evaluating one cylinder instead of the required test average; and rejecting product before investigating the test.