ACI CQTM flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Coefficient of variation
- A relative measure of strength variability: standard deviation divided by mean strength, expressed as a percentage. Lower values indicate tighter quality control of concrete production.
- Required average strength f'cr
- The target mean compressive strength used for mixture proportioning so that test results meet f'c acceptance criteria with a defined probability of failure.
- Standard deviation s
- The statistical spread of compressive strength test results about their mean. It is used to compute f'cr and to gauge process control consistency.
- Acceptance criterion (ACI 318)
- Averages of any three consecutive strength tests must equal or exceed f'c; no single test may fall more than 500 psi below f'c without triggering evaluation.
- Slump test (ASTM C143)
- A field test measuring the vertical drop of a molded concrete cone after removal. It indicates consistency and workability of fresh concrete.
- Air content test
- A field test (pressure or volumetric method) that quantifies entrained air in fresh concrete, which is critical for freeze-thaw durability in cold climates.
- Cylinder curing (ASTM C31)
- Field-cast test cylinders are standard-cured in moist conditions or lime water at controlled temperature before compressive strength testing.
- Quality control plan
- A documented program specifying sampling frequency, test methods, acceptance criteria, and corrective actions to ensure concrete meets specified requirements.
- Trial batch
- A test mixture produced before full-scale production to verify proportions, workability, and strength meet the specified design requirements.
- Statistical process control
- Use of control charts and variability statistics to monitor concrete production, detecting trends or shifts before nonconforming concrete is delivered.
- Compressive strength test
- A destructive test applying axial load to a cured concrete cylinder until failure; the peak load divided by cross-sectional area gives compressive strength.
- Mix design proportioning
- Selecting cement, water, aggregate, and admixture quantities to achieve specified strength, durability, and workability at minimum cost.
- Water-cementitious ratio
- The mass ratio of water to cementitious materials in a mixture. Lower ratios generally increase strength and durability but reduce workability.
- Sampling frequency for tests
- ACI 318 requires strength tests at least once per day of placement, once per 150 yd³, and once per 5000 ft² of slab or wall surface.
- Curing temperature requirement
- Concrete must be maintained above 50 °F during curing so that cement hydration proceeds and design strength can develop.
- Initial curing of field cylinders
- Cylinders stored at the job site must be kept at 60–80 °F and protected from moisture loss for the first 24 hours before transport.
- Concrete slump limits
- Typical slump for normal-weight concrete is 1–4 in.; up to 6 in. is permitted when mechanical consolidation is used per ACI guidance.
- Minimum concrete cover
- The required distance from reinforcement to the concrete surface, protecting steel from corrosion and providing fire resistance; varies with exposure conditions.
- Consolidation by vibration
- Internal vibrators compact fresh concrete, removing entrapped air; they must penetrate the previous lift and be withdrawn slowly to avoid segregation.
- Formwork removal timing
- Side forms may be removed once concrete hardens enough to resist damage; soffit forms depend on member span and strength gain.
- Cold weather concreting
- Protecting concrete from freezing until it reaches at least 500 psi; heated enclosures and insulated forms prevent damage to fresh concrete.
- Hot weather concreting
- Cooling aggregates and water, reducing slump, minimizing placement time, and curing promptly to prevent rapid moisture loss and cracking.
- Construction joint
- A planned stopping point in concrete placement where fresh concrete is later placed against hardened concrete; surface is prepared for bond.
- Contraction joint
- A deliberate groove or weakened plane in a slab that controls where shrinkage cracks occur, keeping cracking orderly and narrow.
- Isolation joint
- A separation between a slab and adjacent structures (walls, columns) that allows independent movement and prevents cracking from restraint.
- Bleed water
- Water that rises to the concrete surface after placement due to settlement of solids; finishing must wait until it evaporates to avoid weak surfaces.
- Finishing sequence
- Strike off, bull float, float, and trowel in order; each step follows evaporation of bleed water to produce a durable, smooth surface.
- Concrete pumping
- Transporting concrete through a pipeline; requires continuous supply, priming of lines, and avoiding long vertical drops that cause segregation.
- Segregation
- Separation of coarse aggregate from mortar in fresh concrete, often caused by over-vibration, excessive drop, or improper handling.
- Freeze protection threshold
- Fresh concrete must be protected from freezing until it attains about 500 psi, the strength at which damage from a freeze cycle is negligible.
- Slab curing methods
- Moist curing, curing compounds, or impermeable covers retain water in concrete so that hydration continues and design strength develops.
- Reinforcement placement
- Steel bars are positioned per drawings with specified cover and spacing; supports (chairs) maintain elevation before concrete is placed.