concrete Flashcards
_____ is the process of maintaining satisfactory moisture content and temperature in the concrete for a definite period of time.
curing
____ is a long-term process and requires water and proper temperature.
hydration of cement
What happens to concrete is not cured and is allowed to dry in air?
it will gain only about 50% of the strength of continuously cured concrete
What happens if concrete is cured for only 3 days?
it will reach about 60% of the strength of continuously cured concrete
What happens of concrete is cured for 7 days?
it will reach 80% of the strength of continuously cured concrete
What happens if curing stops for some time and then resumes again?
the strength gain will also stop and reactivate
_____ increases the rate of hydration and, consequently, the rate of strength of development.
increasing temperature
_____ is usually emphasized and controlled since it is an indication of the concrete quality.
strength
Proper ____ not only increases strength but also provides other desirable properties such as durability, water tightness, abrasion resistance, volume stability, resistance to freeze and thaw, and resistance to deicing chemicals.
curing
What happens if concrete is not cured after setting?
concrete will shrink, causing cracks
_____ can be prevented if ample water is provided for a long period of time.
drying shrinkage
Curing can be performed by any of the following approaches: ____, ____, ____
maintaining the presence of water in the concrete during early ages, preventing loss of mixing water from the concrete by sealing the surface, accelerating the strength gain by supplying heat and additional moisture to the concrete
Methods to maintain the water pressure include ____, _____, _____
ponding or immersion, spraying or fogging, wet coverings
Methods to prevent water loss include _____, ____, _____
impervious papers or plastic sheets, membrane-forming compounds, leaving the forms in place
Accelerated curing methods include ____, ____, _____
curing, insulating blankets or covers, various heating techniques
_____ involves covering the exposed surface of the concrete structure with water.
ponding
This method is suitable for flat surfaces such as floors and pavements, especially for small jobs.
ponding
_____ is used to cure test specimens in the laboratory, as well as other concrete members, as appropriate.
immersion
This method requires a large amount of water and could be expensive. It is most suitable in high temperature and low humidity environments.
spraying or fogging
Moisture-retaining fabric coverings saturated with water, such as burlap, cotton mats, and rugs, are used in many applications.
wet coverings
Evaporation of moisture from concrete can be reduced using _____, such as kraft papers, or plastic sheets, such as polyethylene film.
impervious papers
____ are suitable for horizontal surfaces and simply shaped concrete structures, while ____ are effective and easily applied to various shapes.
impervious papers, plastic sheets
Various types of liquid membrane-forming compounds can be applied to the concrete surface to reduce or retard moisture loss.
membrane-forming compounds
Loss of moisture can be reduced by _____ as long as practical, provided that the top concrete exposed surface is kept wet.
leaving the forms in place
_____ is used when early strength gain in concrete is required or additional heat is needed during cold weather.
steam curing
When the temperature falls below freezing, concrete should be insulated using layers of dry, porous material such as hay or straw.
insulating blankets or covers
____ includes electrically heated steel forms, and electrically heated blankets.
electrical curing
Steel forms can also be heated by circulating ____ around the outside of the structure.
hot oil
The minimum time of curing period depends on several factors, such as _____, ___, ____, ____, ____, ____, _____
type of cement, mixture proportions, required strength, ambient weather, size and shape of the structure, future exposure conditions, and method of curing
The main properties of hardened concrete that are of interest to civil and constructions engineers include the ___, ___, ____, ____
early volume change, creep, permeability, stress-strain relationship
When the cement past is still plastic, it undergoes a slight decrease in volume of about 1%. This shrinkage is known as ____ and is due to the loss of water from the cement paste, either from evaporation or from suction by dry concrete below the fresh concrete.
plastic shrinkage
____ may cause cracking; it can be prevented or reduced by controlling water loss.
plastic shrinkage
If concrete is not properly cured and is allowed to dry, it will shrink. This shrinkage is referred to as ____, and it also causes cracks.
drying shrinkage
Shrinkage is ____ proportional with time.
inversely
Shrinkage and shrinkage-induced cracking are increased by several factors, including ___, ____, ____, ____, ____, ____
lack of curing, high water-cement ratio, high cement content, low coarse aggregate content, existence of steel reinforcement, aging
On the other hand, if concrete is cured continuously in water after setting, ______
concrete will swell very slightly due to the absorption of water
____ is accompanied by a slight increase in weight.
swelling
The heat of hydration can produce two mechanisms that will limit the performance of concrete: _____, _____
if the internal temperature of the hydrating concrete exceeds 158°F, if the thermal differential in the concrete exceeds 35°F thermal cracking can develop
If the internal temperature of the hydrating concrete exceeds 158°F which can result in ______
a delayed ettringite formation, causing long-term durability issues
The ____ indicates thermal control plan should be developed when the minimum dimension of greater than 3 ft.
PCA, Portland Cement Association
Measures that can be taken to minimize the potential for thermally induced stressed include: ___, ___, ____, ___, ____, ____
using a mix design with a low initial heat of hydration by substituting fly ash and/or silica fume for cement, reducing the temperature during mixing by substituting ice for water, placing the concrete in think lifts, insulate forms, embed cooling pipers into the structure, scheduling concrete placement so that the development of the heat of hydration does not correspond with increasing environmental temperatures
____ is defined as the gradual increase in strain, with time, under sustained load.
creep
In simply supported reinforced concrete beams, creep increases the _____, and therefore, increases the stress in the steel.
deflection
_____ is an important factor that largely affects the durability of hardened concrete.
permeability
________ allows water and chemicals to penetrate, which, in turn, reduces the resistance of the concrete structure to frost, alkali-silica reactivity, and other chemical attacks.
permeable concrete
The air voids that do affect permeability of hardened concrete are obtained from two main sources: ___, ____
incomplete consolidation of fresh concrete, voids resulting from evaporation of mixing water that is not used for hydration of cement
_____ the water-cement ratio in fresh concrete has a severe effect on permeability.
increasing
Other factors that affect the permeability include ___, ___, ____
age of concrete, fineness of cement particles, air-entraining agents
_____ reduces the permeability, since hydration products fill the spaces between cement grains.
age
The ____ the cement particles, the faster is the rate of hydration and the faster is the development of impermeable concrete.
finer
_____ indirectly reduce the permeability, since they allow the use of a lower water-cement ratio.
air-entraining agents
____ the water-cement ratio decreases both strength and stiffness of the concrete.
increasing
The stress-strain behavior is close to linear at ____, then becomes nonlinear as ______.
low stress levels, stress increases
With higher water-cement ratios, the stress-strain behavior becomes _____ at smaller strains.
nonlinear
High-strength concrete has _____ characteristics when compared to low-strength concrete.
sharp peaks and sudden failure
The ____ can be defined as the largest stress that does not cause a measurable permanent strain.
elastic limit
The shape of the stress-strain relationship of concrete is almost the same for both compression and tension, although the tensile strength is much _____ than the compressive strength.
smaller
Normal-weight concrete has a modulus of elasticity of _____.
14 to 40 GPa (2000 to 6000 ksi)
Poisson’s ratio can also be determined using ______.
ASTM C469
A value of ____ for Poisson’s ratio is commonly used.
0.15 to 0.20
What is the reason why the stress-strain relationship of concrete is nonlinear?
this behavior is attributed tot he microcracking in concrete at the interface between aggregate particles and the cement paste.
The modules of elasticity ____ when the compressive strength increases.
increases
Probably the most common test performed on hardened concrete is the ______, since it is relatively easy to perform and since there is a strong correlation between the compressive strength and many desirable properties.
compressive strength test
What are other tests in testing of hardened concrete aside from the compressive strength test?
split tension, flexure strength, rebound hammer, penetration resistance, ultrasonic pulse velocity, maturity tests
_____ is one of the main structural design requirements to ensure that the structure will be able to carry the intended load.
compressive strength
Compressive strength _____ as the water-cement ratio decreases.
increases
Designers specify a ____ compressive strength of the concrete to ensure high quality, even if this strength is not needed for structural support.
high
The compressive strength of normal-weight concrete is between _____
20 and 40 Mpa (3000 and 6000 psi)
In the United States, the test is performed on cylindrical specimens and is standardized by _____.
ASTM C39
The standard specimen size for compressive strength test is ______ in diameter and _____ high.
0.15 m (6 in.), 0.30 m (12 in.)
The compressive strength of the specimen is affected by the specimen size. ____ the specimen size reduces the strength because there is a greater probability of weak elements.
increasing
The interface between the _____ and aggregate particles is typically the weakest location within the concrete material.
hardened cement paste
_____ (ASTM C496) measures the tensile strength of concrete.
split-tension test
In split-tension test, a 0.15-m by 0.30-m (6-in. by 12- in.) concrete cylinder is subjected to a compressive load at a constant rate along the _____ diameter until failure.
vertical
Typical indirect tensile strength of concrete varies from ______.
2.5 to 3.1 MPa (360 to 450 psi)
The tensile strength of concrete is about ____ of its compressive strength.
10%
The ______ (ASTM C78) is importsnt for design and construction of road and airport concrete pavements.
flexure strength
The _____ ensures a constant bending moment without any shear force applied in the middle of the specimen.
third-point loading
The _____, also known as the Schmidt hammer test, is a nondestructive test performed on hardened concrete to determine the hardness of the surface.
rebound hammer test
The _____ is commonly used to get an indication of the concrete strength.
rebound hammer
The ____ the rebound, the harder is the concrete surface and, therefore, the greater is the strength.
larger
The ____ can also be used to check uniformity of the concrete surface.
rebound hammer test
The test of very simply to run and is standardized by ASTM C805.
rebound hammer test
The _____, also known as the Windsor Probe test, is standardized by ASTM C803.
penetration resistance test
The instrument is a gunlike device that shoots probes into the concrete surface in order to determine its strength.
penetration resistance test
The amount of penetration of the probe in the concrete is ____ related to the strength of concrete.
inversely
The device is equipped with a special template with three holes, which is placed on the concrete surface.
penetration resistance test
The _____ is expected to provide better strength estimation that the rebound hammer.
penetration resistance test
The ____ (ASTM C597) measures the velocity of an ultrasonic wave passing through the concrete.
ultrasonic pulse velocity test
This test is used to detect cracks, discontinuities, or internal deterioration in the structure of concrete.
ultrasonic pulse velocity test
_____ of a concrete mixture is defined as the degree of cement hydration, which varies as a function of both time and temperature.
maturity
This test (ASTM C1074) is performed on fresh concrete and continued for several days.
maturity test
what are the 12 alternatives to conventional concrete?
self-consolidating concrete, flowable fill, shotcrete, lightweight concrete, heavyweight concrete, high-strength concrete, shrinkage-compensating concrete, polymers and concrete, fiber-reinforced concrete, rolled-compacted concrete, high-performance concrete, pervious concrete
_____, also known as self-compacting concrete is a highly flowable, nonsegregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcement, without any mechanical consolidation (NRMCA).
self-consolidating concrete (SCC)
Two important properties specific to SCC in its plastic state are its ______
flowability and stability
VSI stands for:
visual stability index
____ is a self-leveling and self-compacting, cementitious material with an unconfined compressive strength of 8.3 MPa (1200 psi) or less.
flowable fill
____ is also commonly referred to as controlled low-strength material (CLSM), controlled density fill (CDF), flowable compacting fill, lean fill, unshrinkable fill, flow mortar, fly ash flow, and liquid dirt (NRMCA).
flowable fill
One of the unique properties of flowable fill that makes it advantageous compared with compacted granular fill is its _____.
flowability
_____ is mortar or small-aggregate concrete that is sprayed at high velocity onto a surface.
shotcrete
_____, also known as “gunite” or “sprayed concrete”, is a relatively dry mixture that is consolidated by the impact force and can be placed on vertical or horizontal surfaces without sagging.
shotcrete
Shotcrete is applied by either the ____ or ____ process.
wet, dry
In the ___ process, a pre-mixed blend of cement and damp aggregate is propelled through a hose by compressed air to a nozzle, whole the water is added at the nozzle.
dry
In the ____ process, all ingredients are premixed and pumped through a hose to the nozzle and forced to the surface using compressed air.
wet
Generally, _____ are highly absorptive and can continue to absorb water for an extended period of time.
lightweight aggregates
The specific gravity of heavyweight concrete ranges from _____.
3.4 to 6.5
Concrete made with normal-weight aggregate and having compressive strength greater than _____ is considered to be high-strength concrete.
40 MPa (6000 psi)
The ___ and the ____ are the controlling factors for developing high strength.
porosity of the cement paste, transition zone between the cement paste and the aggregate
____ is marketed as Type K cement.
shrinkage-compensating cement
____ is a mixture of aggregates and a polymer binder.
polymer concrete
The addition of ____ to concrete reduces the workability.
fibers
This material uses a relatively low cement factor, rather than strength.
roller-compacted concrete
The American Concrete Institute (ACI) defined ____ as a concrete that meets special performance and uniformity requirement, which cannot always be obtained using conventional ingredients, normal mixing procedures, and typical curing practices.
high-performance concrete
____ has been developed that is specifically designed to allow water to pass through it.
pervious concrete
