ACI Floor Flatness & Levelness (FF/FL Numbers) 3

Question 1

Which ACI document specifically covers design and construction of slabs-on-ground, including flatness and F-number considerations?

Accepted Answer

ACI 360R

Answer

ACI 211.1

Answer

ACI 305R

Answer

ACI 308R

Question 2

What effect does slab curling (warping from differential drying shrinkage) have on FL numbers measured long after placement?

Accepted Answer

Curling can decrease FL numbers as slab edges lift relative to the center

Answer

Curling improves FL numbers over time as the slab settles

Answer

Curling has no measurable effect on FL numbers

Answer

Curling only affects slab thickness measurements, not F-numbers

Question 3

How are F-numbers statistically calculated from dipstick profiler elevation difference measurements?

Accepted Answer

From the statistical variance of sequential elevation differences, converted to an F-number using a standard formula

Answer

By averaging all raw elevation readings directly

Answer

By taking the maximum deviation and dividing by slab length

Answer

By counting the number of gaps exceeding 1/8 inch under a 10-foot straightedge

Question 4

What does it mean when the FL specification for a concrete floor is listed as 'unspecified' or not applicable?

Accepted Answer

No levelness tolerance is required; only flatness (FF) is enforced

Answer

The floor must be perfectly level with zero deviation

Answer

The floor fails all levelness criteria and must be remediated

Answer

Only manual measurement methods are acceptable for that floor

Question 5

Per ASTM E1155, what is the minimum number of elevation differences required to produce a statistically valid F-number for a floor section?

Accepted Answer

34 elevation differences

Answer

10 elevation differences

Answer

20 elevation differences

Answer

50 elevation differences

Question 6

What construction condition is most likely to produce low FF numbers (poor flatness) in freshly placed concrete?

Accepted Answer

Inconsistent screed strikes causing ridges and low spots during placement

Answer

Using a low water-to-cement ratio mix

Answer

Allowing adequate bleed water evaporation before finishing

Answer

Curing with wet burlap immediately after finishing

Question 7

When a floor FF specification is written as 'FF 50 / FL 35,' what do these two numbers represent?

Accepted Answer

Minimum FF of 50 for flatness and minimum FL of 35 for levelness that the floor must achieve

Answer

50 pounds per square foot load capacity and 35-day cure time

Answer

50 measurement runs required and 35 elevation differences per run

Answer

50% flatness compliance and 35% levelness compliance thresholds