ACI Floor Flatness & Levelness (FF/FL Numbers) 1 — Questions and Answers
Question 1: What do FF and FL numbers measure in concrete slabs?
- FF measures local surface waviness; FL measures overall slope relative to a horizontal datum (Correct answer)
- FF measures slab thickness; FL measures compressive strength
- FF measures surface hardness; FL measures moisture content
- FF measures joint spacing; FL measures crack width
Correct answer: FF measures local surface waviness; FL measures overall slope relative to a horizontal datum
FF (floor flatness) measures local curvature and waviness of the surface, while FL (floor levelness) measures how level the floor is relative to a horizontal datum.
Question 2: What does a higher FF or FL number indicate about a concrete floor?
- More surface defects and cracks
- A flatter and more level floor with smaller deviations (Correct answer)
- Greater slab thickness
- Lower compressive strength
Correct answer: A flatter and more level floor with smaller deviations
F-numbers are inversely related to surface deviation; higher numbers indicate smaller deviations and therefore better flatness and levelness.
Question 3: Which ACI document includes F-number tolerances for floor flatness and levelness?
- ACI 301
- ACI 318
- ACI 117 (Correct answer)
- ACI 360R
Correct answer: ACI 117
ACI 117, 'Specification for Tolerances for Concrete Construction and Materials,' includes F-number tolerances for floor flatness and levelness.
Question 4: What instrument is most commonly used to measure floor flatness F-numbers per ASTM E1155?
- Steel straightedge
- Laser level
- Dipstick profiler (Correct answer)
- Digital micrometer
Correct answer: Dipstick profiler
The dipstick profiler is the standard instrument used to measure floor elevation differences for calculating F-numbers per ASTM E1155.
Question 5: What minimum FF number is typically specified for superflat floors used in very narrow aisle (VNA) warehouses?
- FF 25
- FF 50
- FF 100 (Correct answer)
- FF 75
Correct answer: FF 100
Superflat floors for very narrow aisle (VNA) forklifts typically require FF 100 or higher to ensure safe equipment operation at height.
Question 6: The F-number system was developed primarily to replace which older floor flatness measurement method?
- Profilograph readings
- The 10-foot straightedge method (Correct answer)
- Carpet-bombing elevation surveys
- Mercury level readings
Correct answer: The 10-foot straightedge method
The F-number system replaced the traditional 10-foot straightedge method, providing a more objective and statistically meaningful measurement of floor flatness and levelness.
Question 7: Who is credited with developing the F-number floor flatness and levelness system?
- Joseph Phelan
- Allen Face (Correct answer)
- Robert Ytterberg
- James Warner
Correct answer: Allen Face
Allen Face developed the F-number system in the 1980s, which was subsequently adopted by ACI and ASTM as the standard method for measuring floor flatness and levelness.
ACI Floor Flatness & Levelness (FF/FL Numbers) 1
What do FF and FL numbers measure in concrete slabs?