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
What is the function of a 'jitterbug' (grate tamper) during flatwork placement, and when should its use be limited?
Answer: It forces coarse aggregate below the surface; limit use on slabs that will receive a hard trowel finish
A jitterbug forces coarse aggregate below the surface to create a mortar-rich layer, but overuse can produce a weak surface layer prone to scaling on hard-troweled slabs.
What does 'concrete settlement cracking' refer to in flatwork?
Answer: Cracks that form as fresh concrete settles around reinforcing bars or aggregate
Settlement cracks appear over reinforcing bars or other obstructions as the concrete mass settles downward while still plastic, constrained at those points.
When setting screed guides (wet screeds) for a large slab, the strips should be placed at intervals no greater than:
Answer: The length of the screed board minus 2 feet
Screed guide strips should be spaced no farther apart than the screed length minus 2 feet to ensure both ends of the screed always ride on guides.
Which of the following best describes 'plastic shrinkage cracking' in flatwork?
Answer: Cracking that occurs within the first few hours after placement as moisture evaporates rapidly from the surface
Plastic shrinkage cracks form within hours of placement when the evaporation rate exceeds the bleed water rate, causing surface tension-induced cracking before the concrete sets.
When placing concrete adjacent to a previously placed slab (cold joint scenario), what is the recommended practice?
Answer: Place new concrete against fresh (not fully hardened) concrete whenever possible and vibrate at the joint
Placing new concrete while the adjacent pour is still fresh and vibrating at the interface creates the best bond and reduces the risk of a structural cold joint.
What effect does excessive water added to concrete at the jobsite (retempering) have on flatwork quality?
Answer: It increases shrinkage, reduces strength, and increases the risk of surface defects
Adding water increases the water-cement ratio, which reduces compressive strength, increases drying shrinkage, and promotes surface scaling and dusting.
What is the purpose of 'fogging' or 'misting' the air above fresh concrete during placement on a hot, dry, or windy day?
Answer: To reduce the evaporation rate at the surface and prevent plastic shrinkage cracking
Fogging increases the relative humidity directly above the slab, reducing the evaporation rate and helping prevent plastic shrinkage cracking on exposed flatwork.