ACI flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Water-cementitious ratio

Ratio of water mass to total cementitious material mass in a mix; the primary determinant of strength, permeability, and durability, with lower values yielding stronger, less permeable concrete.

Abrams' strength rule

Empirical relationship stating that concrete compressive strength increases as the water-cement ratio decreases; small reductions in w/c produce significant strength gains.

Absolute volume method

Mixture proportioning approach in which the volume of each ingredient is computed from its mass and specific gravity, and aggregate volume fills the remainder of a unit volume.

Entrained air purpose

Tiny, evenly distributed air bubbles intentionally incorporated by admixtures to provide space for freezing water to expand, greatly improving freeze-thaw durability.

Nominal maximum aggregate size

The smallest sieve through which the entire aggregate sample passes; limited by member dimensions and reinforcement spacing to ensure workability and proper consolidation.

Slump test meaning

A consistency measure of fresh concrete obtained with a standard cone; it indicates workability but does not by itself guarantee placeability or resistance to segregation.

Fly ash effect

Supplementary cementitious material that slows early strength gain but improves long-term strength, reduces permeability, and improves sulfate resistance through pozzolanic reaction.

Batching tolerance water

Acceptable deviation in batch water quantity, commonly about ±1% of the required mass; accurate water batching is essential because w/cm controls strength.

Aggregate moisture correction

Free water on aggregate surfaces must be measured and subtracted from batch water so that the specified water-cementitious ratio is actually achieved in the mix.

Truck mixer revolutions

Concrete typically must be discharged before 300 total drum revolutions or 90 minutes after batching, whichever comes first, unless extended time is approved.

Mixing time requirement

After all materials are charged, concrete is mixed a minimum period, commonly 60–90 seconds in stationary mixers, to ensure uniform distribution of ingredients.

Ready-mix delivery ticket

Record of batch time, mix designation, quantities, water added, and revolution count; serves as the primary documentation of delivery compliance and quality.

Concrete placement temperature

Fresh concrete temperature at placement commonly must fall between about 5 and 35 degrees Celsius, with stricter hot-weather limits often near 32 degrees Celsius.

Free fall limit

Concrete should not drop freely more than about 1.0 to 1.5 meters; greater drops cause segregation, so drop pipes or chutes are used.

Vibrator layer penetration

Internal vibrators should penetrate about 100 to 150 millimeters into the previously placed layer to knit layers together and avoid cold joints.

Vibration completion sign

Consolidation is complete when the surface becomes relatively smooth, large air bubbles stop rising, and the concrete begins to level around the vibrator.

Vibrator spacing rule

Insertion points should be spaced about 1.5 times the vibrator's radius of action, commonly 450 to 600 millimeters apart, for uniform consolidation.

Lateral movement prohibition

Using a vibrator to flow concrete sideways causes segregation; concrete should instead be repositioned with shovels or chutes before consolidation.

Pump mix characteristics

Pumpable concrete requires adequate fines, paste content, and cohesive grading; excessive coarse aggregate or harsh mixes cause blockages in the line.

Bleed water finishing rule

Finishing while bleed water remains on the surface traps water and weakens the top layer, causing dusting and scaling; wait until bleed water disappears.

Curing duration

Concrete should be kept moist continuously for a curing period, commonly 7 days for normal cement and 3 days for high-early-strength cement concrete.

Curing compound application

Curing compounds form a membrane that retains moisture and must be applied as a continuous film to a moist surface immediately after finishing.

Plastic shrinkage cracking

Cracking caused by rapid surface moisture loss when evaporation exceeds bleeding; prevented by fogging, windbreaks, shading, or evaporation retarders.

Control joint depth

Control joints are formed or sawed to about one-quarter of the slab thickness so cracking occurs at a planned location rather than randomly.

Cold weather protection

Concrete must be maintained above about 5 degrees Celsius until it reaches sufficient strength, commonly 3.5 MPa, to resist freezing damage.

Slump tolerance

Permitted variation in slump test results, commonly plus or minus 25 millimeters for slumps up to 100 millimeters and plus or minus 40 millimeters above that.

Air content tolerance

Permitted variation in measured air content of fresh concrete, typically plus or minus 1.5 percentage points for air-entrained concrete.

Strength test acceptance

ACI 318 criteria: no individual strength test below fc' minus 3.5 MPa, and averages of three consecutive tests must equal or exceed fc'.

Cylinder sampling frequency

Strength specimens are commonly taken at least once per 110 cubic meters of concrete or once per day of placement, whichever occurs more often.

ACI 318 scope

Building code requirements for structural concrete, covering design, materials, and construction; it is the primary reference for strength acceptance criteria.

ACI 305 and 306

ACI 305 addresses hot-weather concreting practices, while ACI 306 addresses cold-weather concreting; both cover temperature limits and protection requirements.

Silica dust control

Cutting, grinding, or drilling concrete requires wet methods or local exhaust ventilation plus respiratory protection to limit crystalline silica exposure.

Fall protection threshold

In general construction, fall protection is required at elevations of 1.8 meters (6 feet) or more using guardrails, safety nets, or personal fall arrest.