NCCER Concrete Finishing flashcards
NCCER Concrete Finishing · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Slump test
- ASTM C143 test that measures the vertical drop of a molded concrete cone after the mold is lifted; indicates workability and consistency of the mix.
- Air content test
- ASTM C231 pressure method or ASTM C173 volumetric method; measures entrained air percentage, typically 5 to 7 percent for moderate freeze-thaw exposure.
- Bleed water
- Water that rises to the concrete surface as heavier solids settle; must evaporate or be removed before floating, or the surface becomes weak and prone to dusting.
- Screeding
- Striking off excess concrete to the required grade or elevation using a straightedge, screed board, or laser screed; first step after placement and consolidation.
- Bull float
- Long-handled float with a wide blade used to open the concrete surface, embed aggregate, and knock down ridges left by screeding.
- Darby
- Hand tool with a long straight blade used after bull floating to true the surface, cut high spots, and fill low spots before troweling.
- Power trowel
- Rotating-blade machine that compacts and smooths the surface; used after concrete is firm enough to support it without leaving deep marks.
- Broom finish
- Texture produced by dragging a broom across a floated surface; coarser bristles and deeper drag increase roughness and improve wet slip resistance.
- Exposed aggregate finish
- Finish achieved by retarding the surface set or washing away the top mortar before full set, exposing the coarse aggregate for texture and appearance.
- Stamped concrete
- Patterned finish made by pressing imprint tools or mats into colored, partially set concrete to imitate stone, brick, or tile.
- Control joint depth
- Contraction joints are cut to at least one-quarter of slab thickness, with a 1 in minimum, so the crack forms at the joint rather than randomly.
- Control joint spacing
- For unreinforced slabs, joint spacing is commonly 24 to 36 times slab thickness, adjusted for shrinkage, subgrade friction, and mix design.
- Isolation joint
- A joint that separates a slab from columns, walls, or other fixed elements so movement does not crack the slab; often filled with a compressible material.
- Construction joint
- A planned stopping point in a pour where fresh concrete is placed against set concrete; requires a clean, roughened, and bonded surface.
- Curing compound
- Liquid membrane sprayed on a fresh surface to slow moisture loss; must be applied at the manufacturer's coverage rate and within the specified window.
- Wet curing
- Method using ponding, wet burlap, or continuous sprinkling to keep the concrete surface moist for the specified curing period.
- Plastic sheeting curing
- Polyethylene sheet placed over the concrete to retain moisture; edges must be sealed or weighted to prevent drying from wind.
- Cold-weather protection
- ACI 306 practice of keeping concrete above 40 to 50 degrees F during curing; uses insulation blankets, heaters, or enclosures to prevent freezing damage.
- Hot-weather concreting
- ACI 305 practice of cooling concrete, placing at cooler times, and using evaporation retarders when the evaporation rate exceeds 0.2 lb/sq ft/hr.
- Plastic shrinkage cracking
- Cracks that form in fresh concrete when surface evaporation exceeds bleed water; controlled by windbreaks, fogging, and evaporation retarders.
- Dusting
- Powdery surface caused by a weak top layer, often from floating bleed water into the surface or finishing too early; corrected by proper timing and curing.
- Scaling
- Local flaking of the finished surface, usually from freeze-thaw damage, low air content, or finishing while bleed water is present.
- Delamination
- Separation of a thin top layer from the concrete below, often from troweling too early or trapping air under a dense finish.
- Consolidation
- Removing entrapped air with internal vibrators or spud vibrators; vibrator should be inserted vertically at regular intervals and withdrawn slowly.
- Vibrator spacing
- Internal vibrators are typically spaced at about 1.5 times the radius of action, inserted through the lift, and withdrawn slowly to avoid voids.
- Saw cutting window
- Joints are sawed as soon as concrete is hard enough to resist raveling but before shrinkage cracking begins, often within 4 to 12 hours.
- Evaporation rate
- Rate of moisture loss from the surface, affected by air temperature, concrete temperature, humidity, and wind; above 0.2 lb/sq ft/hr requires protective measures.
- Water-cement ratio
- Ratio of water to cementitious material by weight; lower ratios increase strength and durability but reduce workability.
- Slump and workability
- Slump measures consistency, not strength; adding water increases slump but lowers strength, so plasticizers are used to improve flow without extra water.
- Float finish
- Textured finish left by a float or trowel without further smoothing; provides moderate slip resistance for walks and drives.
- Trowel finish
- Smooth, dense finish produced by power or hand troweling; used indoors and where a hard, easy-to-clean surface is required.
- Curing duration
- Curing period depends on mix and exposure; commonly 7 days for Type I cement and 3 days for high-early-strength, or until specified strength is reached.