07_Concrete_Field Testing and curing
Call Kai
Learn
Practice Test
Spaced Repetition
Match
Flashcards
Knowt Play1/74
There's no tags or description
Looks like no tags are added yet.
Name | Mastery | Learn | Test | Matching | Spaced | Call with Kai | Chat |
|---|
No analytics yet
Send a link to your students to track their progress
75 Terms
What does the slump test measure?
Workability of fresh concrete.
What ASTM standard is used for the slump test?
ASTM C143.
How many layers are used in the slump test?
3 layers.
How many times is each slump-test layer rodded?
25 times per layer.
What ASTM standards are listed for the air test?
ASTM C231 and ASTM C173.
What does the air test relate?
Change in pressure to change in volume (change in air voids).
What two air-test meters are shown?
Pressure (air pot) meter and volumetric air meter.
What ASTM standard is listed for test cylinders?
ASTM C684.
What are the general dimensions of a test cylinder?
Diameter × Height (D × H).
What is the relationship between cylinder height and diameter?
H = 2D.
How is a 6 in. × 12 in. cylinder filled?
3 layers, rodded 25 times per layer.
How is a 4 in. × 8 in. cylinder filled?
2 layers, rodded 25 times per layer.
When are concrete test cylinders typically tested?
At 7 days and 28 days.
What is concrete curing?
Control of temperature and moisture through hydration.
Why must adequate water remain in concrete during curing?
To keep hydration going so concrete continues gaining strength.
What happens to concrete strength as hydration continues?
Strength increases.
What % of 28-day strength does concrete have at 1 day?
About 20–25%.
What % of 28-day strength does concrete have at 3 days?
About 50%.
What % of 28-day strength does concrete have at 7 days?
About 70–80%.
What % of 28-day strength does concrete have at 28 days?
100%.
What % of 28-day strength does concrete have at 90 days?
About 120%.
What % of 28-day strength does concrete have at 180 days?
About 125%.
How does concrete strength change with time?
It increases rapidly at first, then the rate of increase slows.
What happens to strength when the w/c ratio increases?
Strength decreases.
What w/c ratio is needed for complete hydration?
About 0.33.
What happens when the w/c ratio is below 0.5?
The concrete becomes difficult to work with.
About how much cement hydrates in 90 days?
About 90%.
Why is relative humidity important during curing?
It keeps concrete from drying out too quickly.
What does maintaining relative humidity help prevent?
Water evaporation.
What happens if hydration stops?
Concrete starts to shrink.
What happens if concrete is not fully hydrated?
It will not achieve the desired strength.
What minimum RH is needed to keep hydration going?
At least 80% RH.
What controls the rate of concrete drying?
Ambient temperature and humidity.
What properties may concrete fail to achieve without curing?
Strength, watertightness, and durability.
Which becomes stronger: moist-cured or air-cured concrete?
Moist-cured concrete.
Why does air-cured concrete eventually stop gaining strength?
Water loss slows or stops hydration.
According to the slide, what temperature must concrete be maintained above?
50°F.
According to the slide, how long must concrete remain moist after placement?
At least 7 days.
What are the three curing approaches listed?
Maintain mixing water, prevent water loss, and accelerate hydration by heat and moisture.
How can hydration be accelerated during curing?
By heat and moisture.
What materials are listed for curing?
Water, mats/blankets, waterproof paper/plastic sheeting, and liquid membrane-forming compound.
What does burlap do during curing?
Slows evaporation loss and supplies moisture to the concrete.
What does waterproof paper or plastic sheeting do?
Minimizes evaporation loss.
What does a liquid membrane-forming compound do?
Forms a seal that reduces moisture loss.
What materials may make up the liquid membrane compound?
Seal coats, resin, or wax compounds.
What three curing materials are pictured?
Burlap, plastic sheeting, and liquid membrane-forming compound.
What constant temperature range is listed for casting and curing?
40°F to 115°F.
What happens to hydration at higher temperatures?
Hydration becomes more rapid.
What happens to early strength gain at higher temperatures?
Strength develops more rapidly.
What do lower casting temperatures yield?
Higher ultimate strength.
What do lower curing temperatures yield?
Lower ultimate strength, to a point.
Why is below-freezing temperature harmful to hydration?
Water freezes, leaving very little water available to hydrate the cement.
What happens to strength gain below freezing?
Strength-gaining ability is minimized.
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 provides freeze/thaw durability.
What is on the vertical axis of the temperature graph?
Compressive strength.
What is on the horizontal axis of the temperature graph?
Age.
What does the curing-temperature graph show about very high temperature?
Fast early strength gain, but poorer later strength.
What does the graph show for below-freezing concrete?
Very low strength development.
How can mixing water be cooled in hot weather?
Use chipped ice.
How can aggregate and water storage be kept cooler?
Shade the aggregate and water storage tank.
What color should mixer trucks and water tanks be painted for hot weather?
White.
What mixing practice should be avoided in hot weather?
Overmixing.
What are the four hot-weather cooling methods listed?
Chipped ice, shade storage, paint trucks/tanks white, and avoid overmixing.
If the w/c ratio increases, does strength increase or decrease?
Decrease.
If concrete loses moisture too early, what process slows or stops?
Hydration.
If hydration continues, what generally happens to concrete strength?
It continues to increase.
Why is proper curing important?
It helps concrete achieve strength, watertightness, and durability.
What is the main purpose of controlling moisture during curing?
Keep enough water available for hydration.
What is the main purpose of controlling temperature during curing?
Control the rate of hydration and strength development.
At 7 days, approximately how much of its 28-day strength has concrete reached?
70–80%.
Can concrete continue gaining strength after 28 days?
Yes.
What is the 90-day strength compared with 28-day strength?
About 120%.
What is the 180-day strength compared with 28-day strength?
About 125%.