Concrete and Reinforcement
What is the usual size of tie wire for rebar placement?
#16 gauge soft annealed
Welded wire mesh should be placed ___________ from the top of concrete slab surface.
1 1/2"
The diameter of a No. 4 deformed bar is:
1/2"
The term "fine aggregate" refers to well-graded gravel up to:
1/4 inch
When sawing a control joint in a concrete slab, the joint must be a minimum of how deep?
1/4 the thickness
A one car driveway should have a minimum width of?
10'
What is the minimum thickness of concrete footings for fireplaces?
12"
How much does one cubic foot of concrete weigh?
150 lbs.
A two car wide driveway is usually how wide?
18'
Ready mix concrete is purchased by the cubic yard, which is how many cubic feet?
27
Concrete is considered to be fully cured or set after ______________days.
28 days
What is the minimum thickness of concrete used for floors on grade?
3 1/2"
Where concrete is cast against and permanently exposed to the earth, reinforcement steel should be __________________ from the earth.
3"
A number 3 rebar is what diameter?
3/8 inch
The maximum size aggregate is limited to the lesser of:
4 1 One quarter the space between side forms 2 Three quarters the space between reinforcing bars 3 One third the depth of the slab on ground 4 All of the above
Which of the following are true in regard to cold-weather construction?
4 1 calcium chloride is added to concrete to help it set quickly. 2 insulation of straw, hay, or polyethylene is placed around concrete footings. 3 concrete block walls are usually laid with heated mortar. 4 all of the above
Besides ensuring the proper strength of concrete, proper curing of concrete also aids in:
4 1 durability 2 surface soundness 3 reducing cracking 4 all of the above
In comparison to regular concrete, air entrained concrete:
4 1 has more workability 2 is more watertight 3 is more durable in freeze/thaw conditions 4 both a and c
Reinforced concrete is accomplished by adding:
4 1 reinforcing rod 2 welded wire 3 stronger cement 4 either a or b
In cases of severe cold weather exposure, the air content in a concrete mix should be about:
5% to 7%
With the exception of special conditions, maximum delivery time between the water being mixed with the Portland cement in batching and the time of completion of discharge from a transit-mix truck is __________________________.
90 minutes
The timing for the removal of forms is important. The concrete has to achieve a strength great enough to support its own weight and the weight of any construction loads placed upon it. General guidelines for wall and column form removal is _________________________ after placement.
At least 12 hours
For a slab placed below grade, it is necessary to provide at least 4" of crushed gravel or stone. This should be compacted. It will prevent moisture from collecting under the slab. This 4" area is known as ________________________.
Base
The most precise way of positioning rebar for a slab is to use:
Chairs
________________________ are a convenient way to limit the size of the placement of concrete to a manageable volume and are a stopping place for a day's work.
Construction joints
Contraction joints, also known as control joints, in a slab are used to:
Control random cracking
Proper __________________ prevents most problems in the finished concrete. Methods used to ensure a high quality, finished product, include a sprayed on membrane curing compound, polyethylene sheets, waterproof paper or wet burlap.
Curing
Rebar is placed in concrete mainly to improve its compression strength.
False
What is the reason for using fiber reinforcement in concrete?
Improves ductility and reduces surface cracks
In most specifications, adding water to a batch of concrete is permitted only one time at the job site as long as the water/cement ratio is not exceeded. This would be done in order to:
Increase the slump to the level specified in the mix design
A method to prevent cast concrete from excessive shrinking is to:
Lower the cement factor and increase the size of the aggregate
Rebar placement for a footing should be in the ________________________ of the footing depth.
Middle one third
Isolation joints isolate differing parts of a structure to permit independent:
Movement
Concrete that has a lot of Portland cement in the mix may be referred to as:
Rich concrete
If concrete is exposed to de-icers and it is not air entrained, it will:
Scale or spall
When concrete becomes flaky and fragmented on the surface, this is called:
Scaling
Air entrainment protects concrete from frost damage, but also makes concrete more workable. For that reason, not as much water is necessary for the mix.
True
Chairs are classified according to their degree of rust protection. Class #1 is the maximum protection, class #2 is moderate protection, and class #3 is no protection.
True
Concrete cures best in cool, damp environments.
True
Floating of the freshly screeded concrete is accomplished with a wood or magnesium bullfloat which smoothes out, levels, compacts and brings the small particles to the surface for finishing.
True
The reason for tying reinforcing bars with tie wire is to keep the rebar in place while pouring. It does not add any additional stength to the concrete.
True
When pouring concrete, the concrete should be placed near its required point. Excessive handling of the concrete weakens it.
True
What admixture is used to improve the durability of concrete that is exposed to freezing and thawing?
air entraining agents
Accelerators speed up the curing process. Which of the following is an accelerator?
calcium chloride
The most commonly used additive to help concrete set rapidly and more cohesively is:
calcium chloride
Concrete is made by mixing:
cement, sand, water, and gravel
It is necessary to maintain the temperature above 50 degrees in order for concrete to properly:
cure
A slump cone is a metal cone used for:
determining water mix in concrete
The white salty powder that forms on the finished surface of concrete is called ___________.
efflorescence
What is used to prevent concrete from sticking to wood forms?
form release agent (oil)
When water is added to Portland cement it causes the mass to harden. This reaction is called:
hydration
Air entrainment is used for what?
making concrete more durable in freeze/thaw conditions
A control joint allows for what?
movement, expansion or contraction
Pouring concrete on frozen earth is:
never acceptable.
On sidewalk surfaces, it is necessary to broom the surface of concrete to provide a:
non-slip surface
As concrete is placed in a form it needs to be leveled off. This can be done manually or mechanically with a __________________________.
power screed
On large areas, it may be necessary to use a __________________ to finish the surface area.
power trowel
What is the sole purpose for welded wire fabric in a floor slab?
prevent cracks from opening
There are two ways to insure proper curing of concrete: apply water to make up for water lost due to evaporation, and __________________ .
prevent evaporation
On hot sunny days in the summertime, a contractor may decide to use ____________ to slow down the setting time of concrete.
retarders
_________________ concrete is the process of leveling the freshly poured concrete before it is floated.
screeding
A concrete floor may also be called a:
slab
) A _________________ is a 12" high cone which determines the amount of water in the mix.
slump cone
Concrete slabs poured above grade are often supported by ribbed or corrugated steel decking. These forms are called __________ .
stay-in-place forms
Reinforcing steel placed to resist the stresses due to shrinkage and weather changes is called ___________________________.
temperature reinforcement
The thermal process known as hydration refers to:
the curing process
Concrete slabs on grade have a tendency to curl because:
the top cures faster
What is the purpose of adding retarders to a concrete mixture?
to slow down the setting time of concrete
What is a screed?
tool for leveling concrete
What is added to make concrete more workable with less water?
water reducers
Adding too much water to a concrete mix will _______________ it.
weaken
