NICET CMT Concrete flashcards

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

Water-cementitious materials ratio

Ratio of the mass of water to the total mass of cementitious materials in a concrete mixture. Lowering the ratio generally increases strength, reduces permeability, and improves durability.

Type III cement

High-early-strength Portland cement that develops strength faster than Type I and generates more heat of hydration. It is used where early form removal or cold-weather construction requires rapid strength gain.

Air entrainment

Intentional incorporation of tiny air bubbles in concrete to improve resistance to freezing and thawing and deicing salts. Air content increases as nominal maximum aggregate size decreases.

Nominal maximum aggregate size

The largest sieve on which the aggregate is retained, defining the size fraction. It is limited by member dimensions, reinforcement spacing, and slab depth to ensure proper placement.

Fly ash Class F

A pozzolan produced from bituminous coal that reacts with calcium hydroxide to form cementitious compounds. It improves workability, reduces heat, and can mitigate sulfate and alkali-silica attack.

Superplasticizer

A high-range water-reducing admixture that greatly increases slump without adding water. It is used to produce flowing concrete or to reduce water content while maintaining workability.

Specified compressive strength f'c

The 28-day compressive strength of concrete used for structural design and acceptance. Field test results are evaluated statistically against this value using ACI 318 criteria.

Composite sample

A representative sample made by combining several increments taken from the same batch or truck. ASTM C172 requires sampling from the middle portion of the discharge, not the first or last material.

Slump test mold

A 12-inch-high metal cone with a 4-inch top and 8-inch bottom diameter. Concrete is placed in three layers, each rodded 25 times with a 5/8-inch rod.

Slump measurement

The vertical distance from the top of the slumped concrete to the top of the mold, measured to the nearest 1/4 inch. A shear or collapse slump requires a new sample.

Pressure air meter

An ASTM C231 device that applies known pressure to a concrete sample and reads air content from gauge response. The aggregate correction factor must be subtracted from the gauge reading.

Volumetric air test

ASTM C173 method that measures air content by observing the volume change after agitating concrete in water. It requires no aggregate correction and suits lightweight aggregate concrete.

Concrete temperature test

ASTM C1064 procedure using a thermometer immersed at least 3 inches in concrete for 2 to 5 minutes. The reading is reported to the nearest 1°F.

Unit weight of concrete

Mass per unit volume determined by filling a standard measure in three layers, rodding each layer 25 times, striking off, and weighing. It is used to calculate yield and air content.

Field-cured cylinders

Specimens cured in the same environmental conditions as the structure to evaluate curing and protection. They are not used for acceptance of concrete strength unless specified.

Standard curing

Moist curing at 73.5 ± 3.5°F from demolding until test. Standard-cured cylinders are used for acceptance strength tests and must be protected from drying and temperature extremes.

Sulfur mortar cap

A capping method per ASTM C617 that provides a flat, plane surface on a cylinder end. The cap plane must be within 0.002 inch and perpendicular to the cylinder axis.

Unbonded cap

A neoprene pad retained in a steel cap per ASTM C1231, used instead of sulfur mortar. It requires qualification and must fit the cylinder diameter without excessive gap.

Compressive strength formula

Compressive strength equals maximum load divided by cross-sectional area. A 6-inch diameter cylinder has an area of 28.27 square inches; a 4-inch cylinder has 12.57 square inches.

Loading rate C39

The compressive testing machine must apply load at 35 ± 7 psi per second for standard concrete cylinders. A steady rate avoids misleading low or high strength results.

Strength test frequency

ACI 318 requires strength samples at least once per day, once per 100 cubic yards or fraction, and once per 5,000 square feet of slab or wall surface.

Acceptance criteria f'c 5000

For specified strength of 5,000 psi or less, the average of three consecutive strength tests must equal or exceed f'c, and no single test may fall below f'c minus 500 psi.

Acceptance criteria high strength

For specified strength above 5,000 psi, the average of three consecutive strength tests must equal or exceed f'c, and no single test may fall below 0.90 f'c.

Core test acceptance

When strength tests fail, three cores are tested. Their average must equal or exceed 0.85 f'c, and no individual core may fall below 0.75 f'c.

Cold weather concreting

ACI 306 requires concrete temperature to be at least 40°F at placement and protected from freezing. Cold weather can retard setting and damage immature concrete.

Hot weather concreting

ACI 305 limits concrete temperature, typically to 95°F or lower, to reduce rapid slump loss, plastic shrinkage, and reduced strength. Cooling aggregates or water may be needed.

Wet concrete hazard

Fresh concrete is highly alkaline, with a pH near 12 to 13. Prolonged skin contact causes chemical burns, so gloves, boots, and eye protection are required.

Crystalline silica hazard

Cutting, grinding, or drilling concrete creates respirable silica dust that can cause silicosis. Use wet methods, local exhaust ventilation, and appropriate respiratory protection.

Slump reporting precision

Slump is reported to the nearest 1/4 inch. If the test is invalid due to shear or collapse, a new sample must be obtained and the test repeated.

Air content reporting

Air content is reported to the nearest 0.1 percent after applying the aggregate correction factor for pressure meters. Volumetric tests do not use an aggregate correction.

C39 report contents

The compressive strength report includes specimen dimensions, cross-sectional area, maximum load, calculated strength to the nearest 10 psi, age, curing, cap type, and fracture pattern.

Test standard hierarchy

The contract documents specify which ASTM standard and edition govern each test. When conflicts arise, the project specifications and latest referenced edition control unless stated otherwise.