F-number testing should preferably be done within how many hours after concrete placement, and never later than how many hours?

F-number testing should preferably be done within how many hours after concrete placement, and never later than how many hours?

• A. Within 24 hours; not later than 72 hours
• B. Within 6 hours; not later than 24 hours
• C. Within 48 hours; not later than 96 hours
• D. Within 72 hours; not later than 120 hours

Answer: (A)

F-number testing is about capturing the concrete’s behavior in the early stage after placement when it is still plastic enough to respond to finishing and while early strength is developing. That makes the test most meaningful in the first 24 hours, with a hard cutoff so the results are still representative of early-set conditions. Doing it within 24 hours and no later than 72 hours gives useful data to guide finishing, curing, and any needed adjustments before the concrete becomes too hard to reflect early performance. Beyond about three days, the readings lose relevance for early-set behavior, and the test won’t accurately indicate how the surface will behave during finishing.

F-number testing is about capturing the concrete’s behavior in the early stage after placement when it is still plastic enough to respond to finishing and while early strength is developing. That makes the test most meaningful in the first 24 hours, with a hard cutoff so the results are still representative of early-set conditions. Doing it within 24 hours and no later than 72 hours gives useful data to guide finishing, curing, and any needed adjustments before the concrete becomes too hard to reflect early performance. Beyond about three days, the readings lose relevance for early-set behavior, and the test won’t accurately indicate how the surface will behave during finishing.