Concrete(BB-CH6) Flashcards
(True or False) Concrete has high ability to resist stretching, bending, and twisting.
false
What principle factor controls the strength of concrete?
water cement ratio
(True or False) The major factor controlling the durability of concrete is its strength.
true
If more water is added to a concrete mix than is needed to hydrate the cement, the
concrete becomes less_______.
watertight
The production of good concrete is impossible unless good quality materials are used in the
mix, and this mix is properly_______.
worked and cured
Portland cement is manufactured from finely ground limestone mixed with which of the
following materials?
any of the above
For highway construction, Type III Portland cement is sometimes preferred to Type I
because Type III has which of the following characteristics?
shorter curing time
What type of cement was developed for use in areas subject to severe frost and ice
conditions?
air entrained
(True or False) Aggregate is the material combined with cement and water to make
concrete.
true
Concrete is denser and stronger when which of the following conditions is met?
all voids are filled
(True or False) When performing a sieve analysis of aggregate, you should determine the
percentage of material retained on the sieve.
true
(True or False) To prevent aggregate from segregating during stockpiling, you should build
up piles in layers by dumping successive loads alongside each other.
true
In concrete, how is laitance produced?
cement is hydrated with excess water
The proportion of air-entraining agent added to a concrete mix should fall within what
range?
3-7%
(True or False) The accepted use for retarders is to increase the rate of hydration.
false
What is the main reason to store cement in a dry place?
To prevent it from setting too slowly and producing weak concrete
When storing sacks of cement in a warehouse, what is the main reason to stack them close
together?
To restrict the circulation of air between them
Before using warehouse-packed cement, what should you do to make it lump free?
roll the sacks around
(True or False) In a field mix, the number of gallons of water per sack of cement must be
increased to allow for the saturated surface-dry condition of the sand.
false
When available aggregate is 1 1/2 inches, what rule of thumb should you use to calculate
materials required for a proper concrete mix?
rule 42
For each layer of concrete placed in a mold for a slump test, how many times should you
rod the mold?
25
After completing a concrete slump test, you tap the side of the mix and the concrete
crumbles apart. What condition exists?
oversanded mix
The rated capacity of a concrete mixing machine is determined by what factor?
The cubic feet of the mixed concrete
(True or False) In cement batch-plant operations, the aggregate must pass through a
weigh box before being discharged into the mixer.
true
In an 11-S concrete mixer, what maximum size aggregate can you use?
3 in
In an 11-S concrete mixer, when should water be added to the mix?
After all the dry ingredients have been added
You are to charge the skip of an 11-S concrete mixer. In what order should you add the dry
ingredients?
aggregate, cemend, sand
When using a large mixing machine, what minimum time should you mix 2 1/3 cubic yards
of concrete?
2 min 15 sec
It is now 12 noon and you just finished placing concrete. You should make sure the inside
of the mixing drum is cleaned no later than?
1330
When cleaning a mixing drum, you should place the coarse aggregate in the drum and turn
for how long?
5 min
When concrete must be discharged more than 4 feet above the level of placement, why
should it be dumped into an elephant trunk?
to reduce segregation
It is now 12 noon and you begin mixing concrete in a mixing drum. The concrete should be
dumped no later than what time?
1330
What type of concrete mixer can mix concrete en route to the jobsite?
transit mix truck
In building construction, what is the most common type of forming material?
wood
What type of joint should you use to make watertight concrete forms?
tongue and groove
The hydrostatic head exerted on forms during concrete-placing operations normally
continues for what maximum time?
1 1/2 hr
(True or False) Footings for any foundation system should always be placed below the
frost line.
true
An exterior wall that serves as an enclosure and also transmits structural loads to the
foundation is called
both a and b
Which of the following phrases best defines the term “keyway” in a concrete footer?
The indentation in the center of the footer
Horizontal form members that tie prefabricated panels together are called_______.
walers
(True or False) Braces are not part of concrete form design and provide no additional
strength.
true
What type of form-tying device is used with cone nuts?
tie rod
When constructing stair forms, you should extend the platform what approximate distance
past the sides?
12 in
Of the following, which is the best bond breaking agent to use on steel forms?
marine engine oil
(True or False) A light film of rust or mill scale is acceptable on rebar.
true
Which of the following rebar ties should you use when a finished mat is to be lifted by
crane?
saddle tie with a twist
When a column assembly of reinforcing bars is raised into place, the reinforcing steel is tied
to the column form at intervals of
5 ft
(True or False) In footing construction, stones may be used instead of steel supports under
reinforcing bars.
true
A joint that separates a floor slab from a column is called
isolation joint
A joint that allows the transfer of part of the load from one structural element to another
through the use of keys or dowels is called a
construction joint
What type of blade is normally used to cut seasoned concrete?
diamond
(True or False) High quality concrete requires both a well designed mix and good placing
procedures.
true
What is the maximum distance concrete should be dropped from a chute?
4 ft
When placing concrete on a slope, you should start at what position?
bottom only
What is the best tool for compacting concrete?
mechanical vibrator
(True or False) It is permissible to use a mechanical vibrator to move concrete in forms.
false
Which of the following procedures is used to bring a concrete surface to the required
elevation?
screeding
The speed at which a vibrating screed is pulled across concrete directly depends on which
of the following factors?
the slump of the concrete
(True or False) Troweling a vibrator screed finished floor slab is usually delayed because
of the slow setup time needed for the concrete mix.
false
Which of the following finishing tools gives concrete a smooth, dense, finished surface?
steel trowel
Which of the following processes produces a nonskid or rough concrete surface?
brooming
Concrete made with ordinary cement is generally cured for what minimum period?
3 days
(True or False) When curing flat surfaces, ponding allows the concrete to maintain a
uniform temperature.
true
Which of the following materials is the best insulator?
straw
When plastic is used in the concrete curing process, what is the minimum overlap for
adjacent sheets?
12 in
When patching concrete, you should apply mortar in layers NOT exceeding what maximum
thickness?
1/2 in
Of the following surfaces, which is best for precast concrete?
concrete
At what point in concrete casting should the bond-breaking agent be applied to a casting
surface?
after edge forms are placed
What is the simplest method for pickup of small cast panels?
2 point
What is the most common type of brace used in tilt-up concrete construction?
tubular
(True or False) Because of their flexibility and tendency to stretch, cable braces are
unsuitable for most projects.
true
In cast concrete, sand streaking is caused by
escape of moisture from loose forms
Compared to cast-in-place panels, precast panels have what main advantage(s)?
all of the above
