Field Inspection, Quality Control, and Acceptance Decisions
Field inspection, quality control, and acceptance decisions tests whether you can compare field results with the specification and ACI 318 acceptance rules without overstepping. You need to know the strength-test definition, acceptance criteria, and the investigation path for low results.
Inspection and QC
Check batch tickets against the approved mix: cementitious content, w/cm, admixture dosages, aggregate moisture, and yield. Monitor slump, air, and temperature against the project specification. ACI 301 Table 4.2.2 is commonly the source for slump and air tolerances; use the governing specification, not a remembered default.
ACI 318 acceptance
- A strength test is the average of two 6 x 12 in cylinders or three 4 x 8 in cylinders made from one sample.
- Every average of three consecutive strength tests must equal or exceed f'c.
- No individual strength test may fall below f'c − 500 psi when f'c is 5,000 psi or less.
- Field-cured cylinders (C31) show curing adequacy; they are not the basis for acceptance.
Worked example
f'c = 4,000 psi. Three consecutive tests are 3,900, 4,100, and 3,800 psi. The average is 3,933 psi, below 4,000 psi, so the average criterion fails even though 3,800 psi is above the 3,500 psi individual limit. Investigate per ACI 318: cores tested under C42 must average at least 0.85 f'c (3,400 psi) and no core may fall below 0.75 f'c (3,000 psi).
Traps
Using field-cured cylinders for acceptance; treating one cylinder as one test; applying the 500 psi limit to f'c above 5,000 psi; and accepting cores without checking both the average and minimum criteria.