NICET CMT Concrete cheat sheet

w/cm = mass of water ÷ mass of total cementitious materials; increasing w/cm raises permeability and lowers strength.

Type I is general-purpose; Type II has moderate sulfate resistance; Type III is high-early-strength; Type V is for severe sulfate exposure.

Class F fly ash comes from bituminous coal and is pozzolanic; Class C fly ash from lignite or subbituminous coal can have self-cementing properties.

Nominal maximum aggregate size is limited to 1/5 the narrowest member dimension, 1/3 the slab depth, and 3/4 the minimum clear reinforcement spacing.

Air-entrained concrete for severe freeze-thaw exposure typically contains about 5.5% to 7.5% total air, with higher percentages for smaller nominal maximum aggregate sizes.

ACI 211 recommended slumps before admixtures: 1-3 in for foundations and pavements, 2-4 in for beams, walls, and building slabs.

Water reducers increase slump without added water; retarders extend setting time; accelerators shorten setting time and increase early strength.

Sulfate-resistant concrete uses Type II or Type V cement, low C3A, and often fly ash or slag; severe sulfate exposure requires Type V or equivalent performance.

Alkali-silica reaction is mitigated by low-alkali cement, Class F fly ash, slag, or silica fume, and by limiting the alkali content of the concrete.

ASTM C172 sampling: take a composite sample from the middle of discharge, at least three increments, and never the first or last 10% of the load.

For strength tests, the composite sample must be at least 1 ft³; for other tests, obtain a representative sample of sufficient size.

Slump mold: 12 in high, 4 in top diameter, 8 in bottom diameter; fill in three equal layers; rod each layer 25 times with a 5/8-in rod.

Slump test: strike off, remove mold by raising it 5 ± 2 s, and measure the drop to the nearest 1/4 in. Discard shear or collapse slumps.

ASTM C231 pressure air meter: fill in three layers, rod 25 times each, strike off, clamp, inject water, pump to initial pressure, and read air content.

The aggregate correction factor for pressure air meters is determined by testing the coarse and fine aggregate separately and must be subtracted from the gauge reading.

ASTM C173 volumetric air test requires no aggregate correction; it is suitable for lightweight aggregate concrete and for mixtures where pressure methods are unsuitable.

ASTM C1064 temperature: immerse the thermometer at least 3 in in concrete, leave 2-5 min, and read to the nearest 1°F.

ASTM C138 unit weight: fill the measure in three layers, rod 25 blows per layer, strike off, weigh, and compute yield and air content from absolute volumes.

6x12-in cylinders: three layers, 25 rod blows per layer, 5/8-in rod; 4x8-in cylinders: two layers, 25 blows per layer, 3/8-in rod.

Tap the outside of the mold with a mallet after each layer and strike off the top; protect fresh cylinders from freezing and evaporation.

Initial curing: 60-80°F, moist, in the mold for 24 ± 4 h before demolding; standard curing: 73.5 ± 3.5°F, moist, until test.

Field-cured cylinders are cured beside the structure to evaluate curing and protection; standard-cured cylinders are used for acceptance strength.

Sulfur mortar caps per ASTM C617 must be flat within 0.002 in and perpendicular to the cylinder axis; unbonded neoprene caps per ASTM C1231 are an alternative.

Compressive strength = maximum load ÷ cross-sectional area; 6-in diameter area = 28.27 in²; 4-in diameter area = 12.57 in².

ASTM C39 loading rate for standard cylinders is 35 ± 7 psi/s; test 28-day cylinders within ± 20 h of the specified age.

A strength test is the average of at least two 6x12-in cylinders or three 4x8-in cylinders; discard specimens with obvious defects before averaging.

Report strength to the nearest 10 psi and record fracture pattern, cap type, specimen age, and curing history.

ACI 318 strength test frequency: at least once per day, once per 100 yd³ or fraction, and once per 5,000 ft² of slab or wall surface.

For f'c ≤ 5,000 psi: average of three consecutive strength tests ≥ f'c and no individual test < f'c − 500 psi.

For f'c > 5,000 psi: average of three consecutive strength tests ≥ f'c and no individual test < 0.90 f'c.

A strength test is the average of at least two 6x12-in cylinders or three 4x8-in cylinders; one faulty specimen may be discarded if clearly defective.

Core acceptance after failed strength tests: average of three cores ≥ 0.85 f'c and no single core < 0.75 f'c, tested per ASTM C42.

Field inspection verifies forms, reinforcement cover, consolidation, finishing, curing, and protection against hot or cold weather.

Cold weather: maintain concrete at ≥ 40°F at placement and protect from freezing; hot weather: limit concrete temperature to 95°F or lower unless specified.

Quality control uses strength test standard deviation and coefficient of variation to evaluate mixture variability and identify out-of-control production.

Nonconforming strength results trigger investigation, retesting, core testing, load testing, or engineering evaluation before acceptance.

Core ASTM tests: C172 sampling, C143 slump, C231 pressure air, C173 volumetric air, C1064 temperature, C138 unit weight, C31 field cylinders, C192 lab cylinders, C39 compressive strength.

Wet concrete is alkaline (pH 12-13); prolonged skin contact causes chemical burns-use gloves, boots, long sleeves, and eye protection.

Respirable crystalline silica from cutting or grinding concrete causes silicosis; use wet methods, local exhaust, and N95 or better respiratory protection.

Cylinder molds must be labeled with project, mix, truck, location, date, and specimen ID; transport after initial set without impact or freezing.

Slump is reported to 1/4 in, air content to 0.1%, temperature to 1°F, and unit weight to 0.1 lb/ft³.

ASTM C39 report includes specimen diameter, area, maximum load, calculated strength to nearest 10 psi, age, curing, cap type, and fracture pattern.

The contract specifies the governing ASTM edition; when documents conflict, project specifications and referenced standards control.

Records should include sample location, mix ID, truck number, time, slump, air, temperature, unit weight, cylinder IDs, and curing history.

Safety: never stand under suspended loads, use lockout/tagout on testing machines, and keep work areas clear of water and concrete spillage.

Core ASTM tests: C172 sampling, C143 slump, C231 pressure air, C173 volumetric air, C1064 temperature, C138 unit weight, C31 field cylinders, C192 lab cylinders, C39 compressive strength.

Wet concrete is alkaline (pH 12-13); prolonged skin contact causes chemical burns-use gloves, boots, long sleeves, and eye protection.

Respirable crystalline silica from cutting or grinding concrete causes silicosis; use wet methods, local exhaust, and N95 or better respiratory protection.

Cylinder molds must be labeled with project, mix, truck, location, date, and specimen ID; transport after initial set without impact or freezing.

Slump is reported to 1/4 in, air content to 0.1%, temperature to 1°F, and unit weight to 0.1 lb/ft³.

ASTM C39 report includes specimen diameter, area, maximum load, calculated strength to nearest 10 psi, age, curing, cap type, and fracture pattern.

The contract specifies the governing ASTM edition; when documents conflict, project specifications and referenced standards control.

Records should include sample location, mix ID, truck number, time, slump, air, temperature, unit weight, cylinder IDs, and curing history.

Safety: never stand under suspended loads, use lockout/tagout on testing machines, and keep work areas clear of water and concrete spillage.