Flatwork Placement & Leveling Flashcards
7 cards from real ACI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Flatwork Placement & Leveling flashcards as text
When placing concrete in hot weather (above 90°F), which practice best prevents rapid moisture loss during flatwork placement?
Answer: Use sunshades, windbreaks, and mist the subgrade before placement
Sunshades, windbreaks, and pre-moistened subgrade reduce evaporation rate and prevent premature surface drying during hot-weather placement.
What is the primary purpose of using a highway straightedge (10-foot screed) during flatwork leveling?
Answer: To detect and remove high and low spots across the slab
A highway straightedge spans across the slab to identify and correct high and low spots, ensuring a flat, even surface.
During concrete placement, why should concrete not be moved horizontally with a vibrator?
Answer: It causes segregation of aggregates and weakens the concrete
Moving concrete horizontally with a vibrator causes aggregate segregation, pushing coarse particles away and creating weak zones in the slab.
What does 'F-number' (FF/FL) system measure in flatwork?
Answer: Flatness and levelness of the slab surface
The F-number system uses FF (flatness) and FL (levelness) values to quantify surface tolerance and waviness of concrete floors.
Which condition indicates the concrete surface is ready for bull float finishing after screeding?
Answer: Surface water (bleed water) has completely evaporated
Bull floating should begin after initial bleed water disappears so the tool does not trap water beneath the surface, which would weaken it.
When placing concrete for a sloped flatwork slab (e.g., a driveway approach), where should placement begin?
Answer: At the bottom (low end) of the slope
Placement begins at the low end of a slope so that fresh concrete is placed against already-placed concrete, preventing runoff and ensuring proper consolidation.
A concrete slab shows 'blistering' during finishing. What is the most likely cause?
Answer: Sealing or troweling the surface before bleed water and air escape
Blistering occurs when the surface is sealed by premature finishing, trapping bleed water and air beneath a dense mortar layer that later delaminates.