Chapter 10 - Concrete Construction Flashcards
Concrete is produced from __________ cement, coarse and fine ___________ and ________.
Portland / aggregates / water
p 281
- Gravel, stone, sand or other inert materials used in concrete. These materials may be fine or coarse.
Aggregate
p 281
- Maintaining conditions to achieve proper strength during the hardening of concrete.
Curing
p 282
Hardening of concrete involves a chemical process known as ___________.
hydration
p 282
In __________, water combines with the particles of cement to form a microscopic gel.
hydration
p 282
As the concrete hardens, this gel gives off heat, which is known as the _______ of __________.
heat of hydration
p 282
Because hydration involves water, proper curing requires that the concrete be keep ________ until it reaches its desired strength.
moist
p 282
In addition to maintaining proper moisture, concrete that is curing must be maintained at the correct temperature, ideally between ____-____ *F.
50-70
p 283
Concrete that is cured at or above _____ *F will not reach its proper strength; concrete cured near freezing temperatures will harden more _________.
100 / slowly
p 283
In massive concrete structures the _______ ____ ___________ generated can adversely affect the final strength of the concrete.
heat of hydration
p 283
During the curing process concrete will _________ slightly. Theoretically, properly cured concrete continues to harden indefinitely at a gradual rate; however, normal design strength is reached after _____ days.
shrink / 28
p 283
- Ingredients or chemicals added to concrete mix to produce concrete with special characteristics.
Admixture
p 283
Like masonry, concrete is strong in _____________, but weaker in __________.
compression / tension
p 284
The ultimate compressive strength of concrete can be varied from _______ psi to _______ psi with the allowable stress used in design reduced by a factor of safety.
2500 / 6000
p 284
With ____________ reinforcing, steel bars are placed in the formwork and the wet concrete is placed in the formwork around the bars.
ordinary
p 284
The diameters of standard size reinforcing bars vary from _____ inches to ______ inches.
.375 / 2.257
p 284
Concrete beams are frequently cast in the shape of a _____.
tee
p 284
Ordinary reinforcing
The compressive forces in a column could be great enough to cause the steel reinforcing bars to _________ even though they are imbedded in the concrete. To avoid possible buckling, _________ reinforcing is provided around the vertical bars.
buckle / lateral
p 286
In ____________, a compressive force is induced in the concrete before the load is applied.
prestressing
p 286
Prestressing reinforcing
The preloading of the steel creates ____________ stresses in the concrete that counteract the __________ stresses that result when the loads are applied.
compressive / tensile
p 286
Prestressing reinforcing
To compensate for loss of load carrying capacity, the _________ that are initially applied in the prestressing process are slightly higher than the __________ theoretically needed to support the concrete and the applied loads.
forces / forces
p 286
There are two methods of prestressing concrete. These are _______________ and _____________.
pretensioning and postensioning
p 286
In ____________ concrete, steel strands are stretched between anchors producing a ___________ force in the steel. Concrete is then placed around the steel strands and allowed to harden. After the concrete has hardened sufficiently, the force applied to the steel strands is ___________. As the force on the strands is released, the strands exert a _____________ force in the concrete.
pretensioned / tensile / released / compressive
p 286
Pretensioning
When steel strands are released, the concrete member usually takes on a slight ___________ deflection. As loads are applied to the pretensioned member, the deflection usually disappears and the member becomes _______.
upward / flat
p 286
- Reinforcing steel in the concrete is tensioned after the concrete has hardened.
Post-tensioned reinforcing
p 286
Post tensioning
The reinforcing strands are placed in the formwork and covered with __________ or a _________ _________ to prevent binding with the concrete.
grease or a plastic tubing
p 286
Post tensioning
When the concrete has hardened, the strands are __________ against one end of the concrete member and a _______ is positioned at the other end. The jack is used to apply a large _________ force to the steel that stretches the steel and results in a ____________ force in the concrete.
anchored / jack / tensile / compressive
p 286
As general rule, reinforcing steel should not be _______ in the course of fire fighting operations unless it is necessary to rescue trapped victims.
cut
p 287
Cutting through reinforcing steel with a saw or torch is particularly dangerous in _____________ concrete because the steel is not bonded to the concrete. The steel strands are stretched like giant _________ _______. If they are cut, they are likely to _________ out of the concrete, injuring emergency responders.
post tensioned / rubber bands / spring
p 287
Concrete can be either cast ____ ________ or _________.
in place or precast
p 288
- A common type of concrete construction. Refers to concrete that is poured into forms as a liquid and assumes the shape of the form in the position and location it will be used.
Cast-in-Place Concrete
p 288
The single most important factor in determining the ultimate strength of concrete is the ________-to-_________ ratio.
water-to-cement
p 288
The presence of excess moisture in the concrete also produces ___________ in the concrete due to freezing conditions or the heat of a fire.
spalling
p 289
Quality control of concrete
The ________ test is used to check the moisture content of concrete by measuring the amount that a small, cone-shaped sample of the concrete settles or “________” after it is removed from a standard sized test mold.
slump / slumps
p 289
Quality control of concrete
Concrete with a high moisture content has a more liquid consistency and a greater ________.
slump
p 289
Quality control of concrete
Another method of testing concrete is to make small test cylinders of a concrete batch and subject them to ______________ testing. This method is accurate but has the disadvantage of requiring that the concrete be permitted to __________ before tests results are known.
compression / harden
p 289
Concrete framing systems
Steel reinforcing rods will __________ through joints in the concrete to provide continuity of strength between successive pours.
overlap
p 289
Common cast in place structural systems:
- Flat ______
- ______ and _______
- ___________ construction
- slab
- slab and beam
- waffle
p 290
The _____-______ concrete frame is a simple system that consists of a concrete slab supported by concrete columns. The slab of concrete varies in thickness from ____ to ____ inches.
flat-slab / 6 to 12
p 290
A ______ and _______ frame consists of a concrete slab supported by concrete beams. This framing system is extremely light weight and is best suited for buildings with light _______ loads. Slabs in this type of construction can sometimes be as thin as ____ inches.
slab and beam / floor / 2
p 290
Buildings using slab and beam systems are often highly susceptible to fire damage due to their _______ nature.
thin
p 291
The design of this concrete framing system provides a thicker slab while eliminating the weight of unnecessary concrete in the bottom half of the slab ?
Waffle construction
p 291
__________ concrete is placed in forms and cured at a location other than the construction site.
Precast
p 291
- Method of building construction where the concrete building member is poured and set according to specification in a controlled environment and is then shipped to the construction site for use.
Precast concrete
p 291
Advantages to using precast concrete:
- Higher degree of ________ _________ possible than with cast in place concrete
- Work can proceed more _________ at the job site
- Precast concrete sandwich panels can be produced using a polystyrene core, which improves the ____________ properties of the precast concrete
- quality control
- quickly
- insulating
p 292
A major disadvantage to using precast concrete is the need to _______________ the finished components to the job site.
transport
p 293
From a construction standpoint, precast concrete structures have more in common with _______-_________ buildings than with cast-in place concrete buildings.
steel framed
p 293
Precast concrete
Solid slabs are used for short spans up to approximately _____ feet, while the tee slabs can be used for spans up to ______ feet.
30 / 120
p 293
A common form of construction used with precast concrete is known as _____-____ construction.
tilt-up
p 293
- Type of construction in which concrete wall sections (slabs) are cast on the concrete floor of the building and are then tilted up into the vertical position.
Tilt up construction
p 293
Precast structural elements are usually _________ than corresponding cast in place components.
lighter
p 294
A _________, also known as a bracket, is a ledge that projects from the column and supports the beam.
corbel
p 294
- Non bearing exterior wall attached to the outside of a building with a rigid steel frame. Usually the front exterior wall of a building to provide a certain appearance.
Curtain wall
p 295
_____________ concrete systems may be somewhat more vulnerable to failure than ordinary reinforced concrete. This increased vulnerability is due to the fact that the reinforcing cables and rods used in prestressed systems are made of high strength _________ that have lower _______-_______ temperatures.
Prestressed / steels / yield-point
p 295
Concrete structural systems can have fire resistive ratings from ______ to _______ hours.
one to four
p 296
Structural light weight concrete has a lower __________ than ordinary concrete and has a lower thermal _______________.
density / conductivity
p 296
_____________ of concrete is caused primarily by the expansion of the excess moisture within the concrete when it is either heated of when it freezes.
Spalling
p 297
New concrete that is not completely cured is subject to more severe ___________ when exposed to a fire.
spalling
p 297
Because concrete has relatively good insulating properties, it tends to retain the heat of an exposing fire and release it slowly, similar to the manner in which a masonry oven releases heat. This general effect is referred to as the ______ ______ effect.
heat sink
p 297
Cast in place structures have greater inherent _________ than precast structures.
rigidity
p 298
