07_Concrete_Field Testing and curing

What does the slump test measure? | Workability of fresh concrete

What ASTM is used for the slump test? | ASTM C143

How many layers are used in a slump test? | 3 layers

How many times is each slump test layer rodded? | 25 times

What does the air test measure? | Air content/air voids in concrete

What ASTM standards are used for air testing? | ASTM C231 and C173

What are the two common air test meters? | Pressure (air pot) meter and volumetric air meter

What are the common concrete test cylinder sizes? | 6 x 12 in and 4 x 8 in

How is a 6 x 12 in cylinder filled? | 3 layers, rodded 25 times per layer

How is a 4 x 8 in cylinder filled? | 2 layers, rodded 25 times per layer

When are concrete cylinders typically tested? | 7 days and 28 days

What is concrete curing? | Controlling temperature and moisture during hydration

Why is curing important? | It keeps enough water in the concrete for hydration and strength gain

What happens to concrete strength as hydration continues? | Strength increases

How much of its 28-day strength does concrete have after 1 day? | About 20-25%

How much of its 28-day strength does concrete have after 3 days? | About 50%

How much of its 28-day strength does concrete have after 7 days? | About 70-80%

How much of its 28-day strength does concrete have after 28 days? | 100%

Does concrete continue gaining strength after 28 days? | Yes

How much of its 28-day strength can concrete reach at 90 days? | About 120%

How much can it reach at 180 days? | About 125%

What happens to concrete strength when the water-cement ratio increases? | Strength decreases

What w/c ratio is needed for complete hydration? | About 0.33

Why isn't a 0.33 w/c ratio always used? | A w/c ratio below 0.5 can make concrete difficult to work with

About how much cement hydrates within 90 days? | About 90%

Why is relative humidity important during curing? | It keeps concrete from drying out too quickly

What happens if hydration stops? | Concrete starts to shrink and may not reach its desired strength

What relative humidity is needed to keep hydration going? | At least 80%

What controls the rate of concrete drying? | Ambient temperature and humidity

What properties can be hurt by poor curing? | Strength, water tightness, and durability

Which gains more strength, moist-cured or air-cured concrete? | Moist-cured concrete

Why does air-cured concrete gain less strength? | Losing water slows or stops hydration

According to ACI 318, what temperature must curing concrete stay above? | 50°F

According to ACI 318, how long should concrete remain moist after placement? | At least 7 days

What are the three basic curing methods? | Maintain mixing water, prevent water loss, and accelerate hydration with heat and moisture

What materials can be used for curing? | Water, mats or blankets, waterproof paper/plastic sheeting, and liquid membrane-forming compounds

What does burlap do during curing? | Slows evaporation and supplies moisture

What does plastic sheeting do during curing? | Minimizes evaporation

What does a liquid membrane curing compound do? | Seals the surface to reduce moisture loss

What happens when curing temperature increases? | Hydration and early strength gain happen faster

What casting temperature can produce higher ultimate strength? | Lower casting temperatures

What happens to concrete at temperatures below freezing? | Water freezes, reducing hydration and strength gain

What should be done with frozen concrete? | Remove and replace it

What type of concrete is good for cold weather? | Air-entrained concrete

Why is air-entrained concrete good for cold weather? | It improves freeze-thaw durability

How can mixing water be cooled in hot weather? | Use chipped ice

How can aggregates and water tanks be kept cooler? | Keep them shaded

Why can mixer trucks and water tanks be painted white? | To reduce heat absorption

What should be avoided when mixing concrete in hot weather? | Overmixing