ACI Flatwork Finisher key terms

A measure of how wet or workable a fresh concrete mix is, found by measuring how far a standard cone of concrete settles after the mold is lifted.

How easily fresh concrete can be placed, consolidated, and finished without segregating or bleeding. It depends on mix proportions, aggregate shape, and moisture content.

The weight of mixing water divided by the weight of cementitious material in a mix. Lower ratios give stronger, denser concrete but make finishing harder.

Separation of coarse aggregate from the mortar in fresh concrete, often caused by over-vibration, dropping concrete from too high, or adding too much water.

Water rising to the surface of freshly placed concrete as heavier solids settle. Excess bleeding weakens the top layer and can cause dusting or delamination.

Compacting fresh concrete to remove trapped air and voids, usually with a vibrator or by rodding and tamping, so the concrete fully surrounds reinforcement and forms a dense mass.

Mechanical shaking of fresh concrete with an internal or surface vibrator to consolidate it. Over-vibration causes segregation; under-vibration leaves honeycomb and voids.

Voids or cavities left in concrete where mortar failed to fill spaces between coarse aggregate, typically from poor consolidation or a mix that is too stiff.

A straightedge or power tool used to strike off excess concrete and bring the surface to the required grade and plane after placement.

The first finishing step, in which a straightedge or screed is drawn across the formwork to remove surplus concrete and level the surface to final elevation.

A hand or power tool with a flat plate used after strike-off to compact the surface, push down aggregate, and open or close the surface texture before troweling.

A steel-bladed hand or power tool used to smooth and densify the concrete surface, producing a hard, tight finish. Timing depends on when bleed water has disappeared.

A long-handled float used to level and smooth concrete beyond arm's reach right after strike-off, pushing down high spots and filling low spots before bleed water appears.

A tool with a curved lip used to round the top edge of a slab, creating a clean, durable border that resists chipping and spalling.

A tool that cuts a groove in the concrete surface to create a control joint, controlling where shrinkage cracks occur and improving traction.

A deliberate groove or cut in a slab that forces shrinkage cracking to occur along a planned line, keeping the visible surface free of random cracks.

A narrow cut made with a concrete saw to form a control joint after the concrete has hardened enough to resist raveling but before shrinkage cracking begins.

A joint that separates a slab from other structures or slabs, allowing independent movement and preventing restraint from causing cracking.

A gap or compressible filler installed to allow concrete to expand and contract without damaging adjacent structures or slabs.

Maintaining adequate moisture and temperature in concrete after placement so cement hydration can continue, developing strength and durability and reducing surface cracking.

The chemical reaction between cement and water that hardens concrete and generates strength. It requires moisture and slows greatly as temperatures drop.

A liquid applied to hardened concrete that forms a membrane to slow moisture loss, helping the concrete cure when wet curing methods are not used.

A liquid sprayed on fresh concrete to slow surface moisture loss and reduce plastic shrinkage cracking when drying conditions are severe.

A crack that forms in fresh concrete when surface moisture evaporates faster than bleed water can replace it, causing the surface to shrink before it has gained strength.

Volume reduction of hardened concrete as it loses moisture over time. It is the main cause of cracks in slabs and is addressed with control joints.

Separation of a thin top layer of finished concrete from the layer below, often from troweling too early over bleed water or a weak, dusty surface.

A powdery, weak surface layer that wears away easily, usually caused by finishing while bleed water is present, overworking the surface, or inadequate curing.

Chipping or breaking away of concrete at edges, joints, or around reinforcement, often from poor consolidation, freeze-thaw damage, or corrosion of embedded steel.

Flaking or peeling of the finished concrete surface, commonly caused by freeze-thaw cycles, deicing salts, or an overly wet, weak surface layer.

Tiny, evenly distributed air bubbles intentionally added to a concrete mix to improve resistance to freeze-thaw damage and deicing salts.

The standard metal mold used in the slump test to measure the consistency of fresh concrete before it is placed.

A temporary structure that holds fresh concrete in place at the desired shape, line, and grade until it hardens enough to stand on its own.

The required elevation or slope of a concrete surface, set by forms, screeds, or stakes so water drains properly and the slab matches the design.

A high-sheen finish produced by repeated power troweling of a dense, hard concrete surface, often used in polished or industrial floors.

A machine with rotating steel blades used to float and finish large concrete floors, with blade pitch and timing controlling the final surface hardness and sheen.

A sheet placed under a slab to stop moisture from moving up from the subgrade, protecting floor coverings and reducing slab curling and moisture problems.

Warping of a slab when its top dries and shrinks faster than its bottom, causing edges to lift. Moisture control and curing help prevent it.

Compressible material placed in expansion or isolation joints to keep them open and allow movement without concrete-to-concrete contact.