Concrete Flashcards
What is the typical drying time for concrete?
28 days
What is the chemical process for concrete curing?
Hydration
What is considered the “normal” concrete type
Type I Portland Cement
What is Type IA concrete?
Normal concrete, air entrained
What is ‘Air Entraining’?
Tiny bubbles introduced into concrete to help with freeze/thaw cycle
Make concrete more workable
What percentage of air entrained concrete is bubbles?
5%
Where is Type IA concrete typically used?
Cold climates, exposed concrete and mixed climates
What is Type II concrete?
Moderate resistance to sulfates
Where is Type II concrete used?
Below ground when in contact with soil (in particular soil with high sulfate groundwater)
What is Type IIA concrete?
Moderate resistance to sulfates & air entraining
What is Type III concrete?
High early strength concrete
When is Type III concrete used?
Precast concrete - want it cured and out of the factory ASAP
Concrete Block factories, tilt-up construction, anywhere we want to strip formwork early
Also used in cold weather
What is Type IV concrete?
Low heat of hydration
When is Type IV concrete used?
Not often, more for larger structures like dams
What is Type V concrete?
High resistance to sulfate attachedW
What is decorative cement called?
White portland cement
How large should aggregate be in a concrete mix?
Less than 3/4 spacing of the rebar spacing
1/3 depth of the slab
What makes pervious concrete?
Aggregate of the same size
When is lightweight aggregate used in construction?
When a lighter weight is required and/or higher thermal resistance is required
What is used in structural lightweight concrete?
Expanded shale
What is used in non-structural lightweight concrete?
Large air entraining. It’s lighter, a better insulator but lower strength
What defines the strength of concrete?
Water content
What’s the range of PSI of concrete?
2,000 PSI to 20,000 PSI
Normal Concrete -> 3,000 to 4,000 PSI
What are ways of testing concrete strength?
Slump Test
Cylinder Test
Why is pumping concrete horizontally an issue?
Aggregate will settle at the bottom and water will float to the top
How do you prevent concrete from curing too quickly?
Cover it with a plastic sheet
Spray it with water
What are factors that accelerate concrete curing time?
Large concrete slabs
Wind movement over slabs
When is self-consolidating concrete used?
When rebar is crowded in the form
To create crisp edges
What is self-consolidating concrete?
Higher proportion of smaller aggregate & pourability to fill in voids
How can we make concrete a greener material?
Fly-ash concrete
What is fly-ash?
Residue from coal combustion found at bottom of boilers
How does fly-ash make concrete greener?
Fly-ash has heavy metals that create contaminated water.
Storing it in concrete reduces the embodied energy by 1/3
What are 5 qualities of fly-ash concrete?
- Denser
- Stronger
- Shrinks Less
- More resistant to sulfates
- Decreased permeability
Why do concrete and steel work so well together?
They both have almost identical rates of expansion and contraction
Where is reinforcing bar required?
Where the largest tension forces are
Is rebar hot or cold-rolled steel?
Hot rolled steel
What is the diameter of #8 rebar?
8 = 1”
What are the 4 elements that determine rebar spacing?
- Structural requirements
- Aggregate spacing
- Top cover (above rebar)
- Corrosion
What is Grade 60 rebar?
60k psi
60,000 psi
Most common type of rebar
