Flashcards in CONCRETE Deck (50):
What is the most common material for formwork?
Plywood (... With oil, plastic coating, or other non resistant)
What are form ties?
Metal wires or rods used to hold opposite sides of the form together and to prevent their collapse
What is slip forming?
When the form moves as the concrete cures... Forming continuous surfaces such as tunnels and high-rise building cores
How fast does a slip form move?
6-12 inches per hr
What are flying forms?
Large fabricated sections of formwork that are removed and re-used to form an identical section somewhere else ... In big repetitive buildings
Concrete work isn't perfect... What is the tolerance for columns piers and walls?
1/4 inch in 10 ft
Concrete work isn't perfect... What is the tolerance for slabs on grade vs finish concrete floors?
Slab on grade: 1/2 inch in 10
FF: 1/8 inch in 10 ft
Concrete work isn't perfect... What is the tolerance for The total height of interior versus exterior columns?
Interior : one inch in 100 feet
Corner columns: 1/2 inch in 100 feet
In addition to providing a vapor barrier water problems inside a concrete building can be minimized with...
A low water – cement ratio ... Plenty of time to cure before interior finishes applied
What is a perm?
Passage of 1 grain of vapor per hour through 1 sf of material
... At a pressure differential of 1 inch of mercury between the two sides of the material
What are the two common spacings for welded wire fabric?
4 inches or 6 inches
What do rebars sit on?
There are 5 types of cement. Tell me what they are.
Type I - Standard or normal
Type II - modified cement, for a massive structures where heat of hydration needs to be controlled…
Type III - high early strength cement ... Quick set
Type IV - Low heat cement… Used in massive structures to minimize cracking
Type V - sulfate – resisting cement… For structure as opposed to water or high alkaline
What is hydration?
The chemical hardening of concrete
Why does concrete water need to be potable?
Concrete can only drink water without impurities to make sure foreign matter doesn't interfere with adhesion to the cement paste
Hydration requires what water-cement ratio? Workability requires how much extra?
25%… An additional 10% to 15%
What is laitance and why?
Chalky substance on the mix... Too much water
What is the common percentage of water to cement by weight?
0.35 to 0.40
Aggregates make up what percentage of concrete by volume?
70% to 75%
What does an air – entraining agent do?
Tiny bubbles increase workability and durability… Also resistance to freezing and thawing
What do accelerators do?
Speed up hydration
What do plasticizers do?
Reduce need for water while maintaining consistency ... I.e higher strength concrete
What do retarders do?
Slow down hydration to lower heat of hydration
What does fly ash do?
Increases strength, decreases permeability, reduces temperature rise, increases sulfate resistant, and improves workability!
What is autoclaved aerated concrete?
Precast with added aluminum powder in molds... Less density and therefore cuttable with woodworking tools ... Limited structural abilities
What is self-consolidating concrete?
A super plasticizer takes away need for vibration which means less labor
What is carbon fiber concrete?
Instead of steel mesh... Epoxy coated carbon fiber is non corrosive and needs less conc coverage. .. Requires smaller foundations and support structures
Poured gypsum decks are used for...
A very fire-resistant roof
Similar to concrete in that liquid is poured over reinforcing (wire mesh)
You can also buy precast
What does the cylinder test measure? ... What about core cylinder test?
Compressive strength. Tested in lab after different periods of curing time
Core cylinder test is when structure is in place... Core take out then tested
Kelly ball test
Like the slump test -- you see how far a stl ball drops into freshly laid concrete
Why is the impact hammer test The only non-destructive way to test concrete strength after hardening?
A spring-loaded plunger is snapped against concrete surface and amount of rebound measured
K slump test
Syringe on concrete -- comparable to slump test
What does the calcium chloride test measure?
Also called the moisture dome test… It measures moisture in concrete… Inexpensive and easy!
How does the hygrometer test work?
Measures the relative humidity of the atmosphere adjacent to the slab
What is the polyethylene sheet test?
Seal a sheet of plastic to floor ... In 16 hours is there visible moisture?
The electrical impedance test measures moisture in concrete by
Measuring conductance and capacitance
When high alkalinity dissolves sand and rock in the concrete
What does a titration test measure?
What is honeycombing?
Formation of air pockets within concrete and next to forms
Describe scrubbed concrete
Describe an acid wash finish
Brings out full color of the aggregate
Describe water jet finish
How do you strike off concrete?
Pull a straight edge over the freshly
Finished concrete slab
What does it mean to float a slab?
Smoothing a finer cement paste over the coarse aggregate ... Giving it a "float finish"
How is a bull float different than a standard hand held float?
Longer, with longer handle -- worker can stand away
Hard steel troweled finish creates...
A very smooth surface
Broom finish creates
A rough-textured non-slip surface for outdoor
Tell the crack where to be
Construction joints ... How to
Between two successive pours ... You can use a water stop