Concrete Flatwork Finishing Flashcards
6 cards from real ACI Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Concrete Flatwork Finishing flashcards as text
What is 'plastic shrinkage cracking' in concrete flatwork, and what conditions promote it?
Answer: Surface cracking that occurs before the concrete sets when the evaporation rate from the surface exceeds the bleeding rate, often during hot, dry, or windy conditions
Plastic shrinkage cracks form in fresh concrete when rapid surface evaporation creates tensile stresses in the weak, plastic paste; hot, dry, low-humidity, and windy conditions dramatically increase evaporation rates.
Which admixture is most effective at reducing drying shrinkage and curling in concrete flatwork?
Answer: Shrinkage-reducing admixture (SRA)
Shrinkage-reducing admixtures (SRAs) reduce the surface tension of pore water in the cement paste, which is the primary driving force of drying shrinkage, resulting in less curling and fewer contraction cracks.
According to ACI 302.1R, what is the required F-number flatness rating for a 'superflat' floor used with guided vehicles in defined traffic lanes?
Answer: FF 100 / FL 50 (defined traffic area)
ACI 302.1R classifies superflat floors as requiring FF 100 / FL 50 in defined traffic areas; these floors are used in high-bay warehouses with wire-guided or rail-guided forklifts operating at speed.
What is the purpose of applying a curing compound to freshly finished concrete flatwork?
Answer: To retain moisture in the concrete and promote continued cement hydration by forming a membrane that reduces evaporation
Curing compounds (ASTM C309) form a water-retentive membrane on the concrete surface to reduce moisture loss, keeping the relative humidity above 80% needed for continued cement hydration.
What is 'delamination' in concrete flatwork, and how can finishers prevent it?
Answer: A subsurface void layer trapped beneath a troweled skin caused by finishing over bleed water or entrained air, prevented by waiting for bleed water to evaporate and not over-finishing
Delamination forms when finishing seals the surface before bleed water and air escape, creating a thin, weak skin above a void layer; waiting for full bleed water evaporation and avoiding premature power troweling prevents it.
What is the recommended contraction joint spacing formula provided by ACI 302.1R for plain (unreinforced) slabs-on-grade?
Answer: Joint spacing in feet should not exceed 2 to 3 times the slab thickness in inches (e.g., a 4-inch slab: 8–12 ft spacing)
ACI 302.1R recommends joint spacing of 2–3 times the slab thickness in inches, expressed in feet; for a 4-inch slab this yields 8–12-foot joint panels.