ACI CTCI common mistakes
ACI CTCI · Understand the traps and how to avoid them.
Reporting a slump result as a single value from a single measurement rather than recognizing when the test is invalid and must be repeated on a fresh sample.
Candidates memorize the procedure but not the validity criteria, so they report a slump that fell outside the acceptable spread or was obtained after the sample sat too long, treating a failed test as a passing result.
What to do instead
Before recording, confirm the sample was obtained and tested within the allowed time, the mold was lifted steadily without lateral motion, and the result meets the repeatability requirement; if not, discard and retest on a new portion rather than averaging bad data.
Accepting a cylinder set as compliant without verifying that the number of specimens, curing history, and test age match the specification for the acceptance criterion being applied.
Candidates conflate the lab's routine strength report with acceptance testing, so they sign off on a set that was field-cured when it should have been standard-cured, or tested at the wrong age, without flagging the mismatch.
What to do instead
Establish the acceptance criterion first (which specimens, which cure, which age), then check each specimen's chain of custody against it; document any deviation and require a new set rather than interpreting nonconforming data.
Failing to verify that the air content test method selected matches the aggregate size and concrete type before recording a result.
Candidates learn one air meter method and apply it universally, not recognizing that some methods are unsuitable for certain aggregate sizes or concretes, producing a number that looks plausible but is invalid.
What to do instead
State the applicable method for the concrete being tested before testing, confirm the meter is calibrated and the aggregate size is within the method's range, and reject the result if the method is outside its applicability.
Treating a strength test result that falls below the specified strength as an automatic rejection of the concrete, without applying the specified acceptance and investigation provisions.
Candidates reduce acceptance to a single comparison against f'c, missing that acceptance is based on statistical criteria over sets of results and that a low result triggers investigation, not automatic rejection.
What to do instead
Apply the acceptance criteria as written for the number of specimens and results available; when a criterion is not met, follow the investigation steps (evaluate, core test if required) rather than declaring the concrete rejected.
Performing a field test on a sample that was not obtained in accordance with the sampling requirements, then defending the result because the test procedure itself was correct.
Candidates focus on the test apparatus and procedure and treat sampling as a formality, so a nonrepresentative sample is tested correctly and the resulting data are meaningless.
What to do instead
Verify sample location, number of increments, and compositing before any test begins; if the sample does not meet the sampling requirement, obtain a new sample and document why the first was discarded.
Inspecting formwork and reinforcement against a mental checklist instead of the approved drawings and specifications, and accepting work that differs from the documents.
Candidates rely on general good-practice knowledge and miss project-specific requirements such as cover, bar spacing, and form tolerances that are stated in the contract documents.
What to do instead
Inspect with the approved drawings and specification sections open, verify each item against the stated dimension or tolerance, and record deviations with location and disposition rather than approving from memory.
Approving a placement or pour without confirming that required pre-placement inspections and hold points were completed and documented.
Candidates treat inspection as a continuous activity and lose track of mandatory hold points, so work proceeds past a point that required explicit sign-off.
What to do instead
Maintain the inspection and test plan with its hold points, confirm each required sign-off exists before releasing the next activity, and stop work at an unmet hold point rather than allowing it to be covered up.
Recording an inspection observation without a specific location, dimension, or reference to the requirement, making the report unusable for correction.
Candidates write narrative impressions ('cover looked low') because they are documenting activity rather than documenting a verifiable condition against a requirement.
What to do instead
Write each observation as requirement, measured or observed condition, location, and disposition; if a measurement was not taken, take it before writing the entry.
Accepting a curing method based on its presence rather than verifying duration, timing of application, and continuity through the curing period.
Candidates see curing compound or wet cover in place and check the box, without confirming it was applied at the right time or maintained for the required duration, especially across weekends and weather changes.
What to do instead
Verify curing against the specified method, start time, and duration, and check continuity at each visit; document any interruption and the corrective action taken.
Failing to recognize when a test or inspection result requires notification and escalation, and instead recording the result and moving on.
Candidates see their role as data collection and are uncomfortable with the authority to stop or escalate, so nonconforming results are filed rather than acted on.
What to do instead
Know in advance which results are nonconforming and who must be notified; when a result crosses that threshold, issue the notification and document the response, treating escalation as part of the inspection duty.