ACI Flatwork Finisher cheat sheet

Concrete is proportioned by volume or weight; a 1:2:3 mix means 1 part cement, 2 parts fine aggregate, 3 parts coarse aggregate.

Water-cement ratio (w/c) = weight of water divided by weight of cement; lower w/c raises strength and reduces permeability.

Slump test (ASTM C143) measures consistency; typical flatwork slumps are 3-5 in (75-125 mm) without admixtures.

Air content in air-entrained concrete for flatwork is typically 5-7% for 3/4 in aggregate in severe freeze-thaw exposure.

Standard cure time before foot traffic is roughly 24 hours; full design strength is reached at 28 days.

A cubic yard of concrete = 27 cubic feet; volume = length x width x thickness (all in feet) divided by 27.

Hydration is the chemical reaction of cement with water; it consumes water and generates heat (heat of hydration).

Aggregates typically make up 60-75% of concrete volume; paste (cement + water) makes up the remainder.

Bull floating is done after bleed water disappears and before initial set to level ridges and consolidate the surface.

Troweling too early or with bleed water present traps water under a densified surface, causing blistering or delamination.

Edging forms a rounded 1/4-1/2 in radius on slab edges to resist chipping; jointing tools cut control joints to about 1/4 slab depth.

Control joints should be spaced at roughly 24-36 times slab thickness in inches (e.g., 4 in slab = 8-12 ft spacing).

A magnesium float opens the surface; a steel trowel densifies and produces a hard, smooth finish.

Broom finish is produced by dragging a dampened broom perpendicular to traffic direction for slip resistance.

Curing compound should be applied as soon as finishing is complete and surface water has sheen disappeared, per manufacturer rate.

Concrete should not be finished while bleed water is on the surface; wait for it to evaporate or use a retarder.

Evaporation rate above 0.1 lb/ft^2/hr (approximately 1 kg/m^2/hr) raises plastic shrinkage cracking risk; use windbreaks, fog spray, or evaporation retarder.

Hot-weather concreting: limit concrete temperature to about 90 F (32 C); cool aggregates or use ice to control placement temperature.

Cold-weather concreting: protect concrete at 50 F (10 C) minimum until it reaches 500 psi to prevent freeze damage.

Plastic shrinkage cracks form within hours of placement and are typically parallel, shallow, and irregular; they appear before hardening.

Drying shrinkage cracks are longer and occur weeks to months after placement due to moisture loss; control joints manage their location.

A retarder extends set time in hot weather; an accelerator shortens set time in cold weather; both change w/c behavior.

Superplasticizers increase slump without added water; slump loss can occur within 30-90 minutes, so placement timing matters.

Surface defects: crazing is a network of fine cracks from rapid surface drying; scaling is surface flaking from freeze-thaw or deicing salts.

Industrial slabs often specify 4,000-5,000 psi compressive strength with low w/c (0.40-0.45) and air entrainment where exposed.

Flatness is measured by F-numbers: FF (floor flatness) and FL (floor levelness); higher FF indicates a flatter floor.

FF 25/FL 20 is a common random-traffic specification; FF 50+ is typical for narrow-aisle warehouse floors.

Saw-cut joints in industrial slabs are typically cut within 6-12 hours of finishing, before random cracking begins.

Joint spacing for industrial slabs often uses 24-30 times slab thickness; thicker slabs (6-8 in) allow wider spacing.

Steel fiber or macro-synthetic fiber reinforcement reduces plastic shrinkage cracking and improves impact resistance.

Laser screeds and ride-on trowels improve flatness; verify FF/FL with a dipstick or F-meter per ASTM E1155.

Shrinkage-compensating concrete or shrinkage-reducing admixtures are used where joint spacing must be increased.