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concrete Flashcards

1
Q

_____ is the process of maintaining satisfactory moisture content and temperature in the concrete for a definite period of time.

A

curing

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2
Q

____ is a long-term process and requires water and proper temperature.

A

hydration of cement

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3
Q

What happens to concrete is not cured and is allowed to dry in air?

A

it will gain only about 50% of the strength of continuously cured concrete

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4
Q

What happens if concrete is cured for only 3 days?

A

it will reach about 60% of the strength of continuously cured concrete

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5
Q

What happens of concrete is cured for 7 days?

A

it will reach 80% of the strength of continuously cured concrete

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6
Q

What happens if curing stops for some time and then resumes again?

A

the strength gain will also stop and reactivate

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7
Q

_____ increases the rate of hydration and, consequently, the rate of strength of development.

A

increasing temperature

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8
Q

_____ is usually emphasized and controlled since it is an indication of the concrete quality.

A

strength

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9
Q

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.

A

curing

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10
Q

What happens if concrete is not cured after setting?

A

concrete will shrink, causing cracks

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11
Q

_____ can be prevented if ample water is provided for a long period of time.

A

drying shrinkage

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12
Q

Curing can be performed by any of the following approaches: ____, ____, ____

A

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

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13
Q

Methods to maintain the water pressure include ____, _____, _____

A

ponding or immersion, spraying or fogging, wet coverings

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14
Q

Methods to prevent water loss include _____, ____, _____

A

impervious papers or plastic sheets, membrane-forming compounds, leaving the forms in place

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15
Q

Accelerated curing methods include ____, ____, _____

A

curing, insulating blankets or covers, various heating techniques

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16
Q

_____ involves covering the exposed surface of the concrete structure with water.

A

ponding

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17
Q

This method is suitable for flat surfaces such as floors and pavements, especially for small jobs.

A

ponding

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18
Q

_____ is used to cure test specimens in the laboratory, as well as other concrete members, as appropriate.

A

immersion

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19
Q

This method requires a large amount of water and could be expensive. It is most suitable in high temperature and low humidity environments.

A

spraying or fogging

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20
Q

Moisture-retaining fabric coverings saturated with water, such as burlap, cotton mats, and rugs, are used in many applications.

A

wet coverings

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21
Q

Evaporation of moisture from concrete can be reduced using _____, such as kraft papers, or plastic sheets, such as polyethylene film.

A

impervious papers

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22
Q

____ are suitable for horizontal surfaces and simply shaped concrete structures, while ____ are effective and easily applied to various shapes.

A

impervious papers, plastic sheets

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23
Q

Various types of liquid membrane-forming compounds can be applied to the concrete surface to reduce or retard moisture loss.

A

membrane-forming compounds

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24
Q

Loss of moisture can be reduced by _____ as long as practical, provided that the top concrete exposed surface is kept wet.

A

leaving the forms in place

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25
Q

_____ is used when early strength gain in concrete is required or additional heat is needed during cold weather.

A

steam curing

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26
Q

When the temperature falls below freezing, concrete should be insulated using layers of dry, porous material such as hay or straw.

A

insulating blankets or covers

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27
Q

____ includes electrically heated steel forms, and electrically heated blankets.

A

electrical curing

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28
Q

Steel forms can also be heated by circulating ____ around the outside of the structure.

A

hot oil

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29
Q

The minimum time of curing period depends on several factors, such as _____, ___, ____, ____, ____, ____, _____

A

type of cement, mixture proportions, required strength, ambient weather, size and shape of the structure, future exposure conditions, and method of curing

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30
Q

The main properties of hardened concrete that are of interest to civil and constructions engineers include the ___, ___, ____, ____

A

early volume change, creep, permeability, stress-strain relationship

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31
Q

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.

A

plastic shrinkage

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32
Q

____ may cause cracking; it can be prevented or reduced by controlling water loss.

A

plastic shrinkage

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33
Q

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.

A

drying shrinkage

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34
Q

Shrinkage is ____ proportional with time.

A

inversely

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35
Q

Shrinkage and shrinkage-induced cracking are increased by several factors, including ___, ____, ____, ____, ____, ____

A

lack of curing, high water-cement ratio, high cement content, low coarse aggregate content, existence of steel reinforcement, aging

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36
Q

On the other hand, if concrete is cured continuously in water after setting, ______

A

concrete will swell very slightly due to the absorption of water

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37
Q

____ is accompanied by a slight increase in weight.

A

swelling

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38
Q

The heat of hydration can produce two mechanisms that will limit the performance of concrete: _____, _____

A

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

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39
Q

If the internal temperature of the hydrating concrete exceeds 158°F which can result in ______

A

a delayed ettringite formation, causing long-term durability issues

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40
Q

The ____ indicates thermal control plan should be developed when the minimum dimension of greater than 3 ft.

A

PCA, Portland Cement Association

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41
Q

Measures that can be taken to minimize the potential for thermally induced stressed include: ___, ___, ____, ___, ____, ____

A

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

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42
Q

____ is defined as the gradual increase in strain, with time, under sustained load.

A

creep

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43
Q

In simply supported reinforced concrete beams, creep increases the _____, and therefore, increases the stress in the steel.

A

deflection

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44
Q

_____ is an important factor that largely affects the durability of hardened concrete.

A

permeability

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45
Q

________ 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.

A

permeable concrete

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46
Q

The air voids that do affect permeability of hardened concrete are obtained from two main sources: ___, ____

A

incomplete consolidation of fresh concrete, voids resulting from evaporation of mixing water that is not used for hydration of cement

47
Q

_____ the water-cement ratio in fresh concrete has a severe effect on permeability.

A

increasing

48
Q

Other factors that affect the permeability include ___, ___, ____

A

age of concrete, fineness of cement particles, air-entraining agents

49
Q

_____ reduces the permeability, since hydration products fill the spaces between cement grains.

A

age

50
Q

The ____ the cement particles, the faster is the rate of hydration and the faster is the development of impermeable concrete.

A

finer

51
Q

_____ indirectly reduce the permeability, since they allow the use of a lower water-cement ratio.

A

air-entraining agents

52
Q

____ the water-cement ratio decreases both strength and stiffness of the concrete.

A

increasing

53
Q

The stress-strain behavior is close to linear at ____, then becomes nonlinear as ______.

A

low stress levels, stress increases

54
Q

With higher water-cement ratios, the stress-strain behavior becomes _____ at smaller strains.

A

nonlinear

55
Q

High-strength concrete has _____ characteristics when compared to low-strength concrete.

A

sharp peaks and sudden failure

56
Q

The ____ can be defined as the largest stress that does not cause a measurable permanent strain.

A

elastic limit

57
Q

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.

A

smaller

58
Q

Normal-weight concrete has a modulus of elasticity of _____.

A

14 to 40 GPa (2000 to 6000 ksi)

59
Q

Poisson’s ratio can also be determined using ______.

A

ASTM C469

60
Q

A value of ____ for Poisson’s ratio is commonly used.

A

0.15 to 0.20

61
Q

What is the reason why the stress-strain relationship of concrete is nonlinear?

A

this behavior is attributed tot he microcracking in concrete at the interface between aggregate particles and the cement paste.

62
Q

The modules of elasticity ____ when the compressive strength increases.

A

increases

63
Q

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.

A

compressive strength test

64
Q

What are other tests in testing of hardened concrete aside from the compressive strength test?

A

split tension, flexure strength, rebound hammer, penetration resistance, ultrasonic pulse velocity, maturity tests

65
Q

_____ is one of the main structural design requirements to ensure that the structure will be able to carry the intended load.

A

compressive strength

66
Q

Compressive strength _____ as the water-cement ratio decreases.

A

increases

67
Q

Designers specify a ____ compressive strength of the concrete to ensure high quality, even if this strength is not needed for structural support.

A

high

68
Q

The compressive strength of normal-weight concrete is between _____

A

20 and 40 Mpa (3000 and 6000 psi)

69
Q

In the United States, the test is performed on cylindrical specimens and is standardized by _____.

A

ASTM C39

70
Q

The standard specimen size for compressive strength test is ______ in diameter and _____ high.

A

0.15 m (6 in.), 0.30 m (12 in.)

71
Q

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.

A

increasing

72
Q

The interface between the _____ and aggregate particles is typically the weakest location within the concrete material.

A

hardened cement paste

73
Q

_____ (ASTM C496) measures the tensile strength of concrete.

A

split-tension test

74
Q

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.

A

vertical

75
Q

Typical indirect tensile strength of concrete varies from ______.

A

2.5 to 3.1 MPa (360 to 450 psi)

76
Q

The tensile strength of concrete is about ____ of its compressive strength.

A

10%

77
Q

The ______ (ASTM C78) is importsnt for design and construction of road and airport concrete pavements.

A

flexure strength

78
Q

The _____ ensures a constant bending moment without any shear force applied in the middle of the specimen.

A

third-point loading

79
Q

The _____, also known as the Schmidt hammer test, is a nondestructive test performed on hardened concrete to determine the hardness of the surface.

A

rebound hammer test

80
Q

The _____ is commonly used to get an indication of the concrete strength.

A

rebound hammer

81
Q

The ____ the rebound, the harder is the concrete surface and, therefore, the greater is the strength.

A

larger

82
Q

The ____ can also be used to check uniformity of the concrete surface.

A

rebound hammer test

83
Q

The test of very simply to run and is standardized by ASTM C805.

A

rebound hammer test

84
Q

The _____, also known as the Windsor Probe test, is standardized by ASTM C803.

A

penetration resistance test

85
Q

The instrument is a gunlike device that shoots probes into the concrete surface in order to determine its strength.

A

penetration resistance test

86
Q

The amount of penetration of the probe in the concrete is ____ related to the strength of concrete.

A

inversely

87
Q

The device is equipped with a special template with three holes, which is placed on the concrete surface.

A

penetration resistance test

88
Q

The _____ is expected to provide better strength estimation that the rebound hammer.

A

penetration resistance test

89
Q

The ____ (ASTM C597) measures the velocity of an ultrasonic wave passing through the concrete.

A

ultrasonic pulse velocity test

90
Q

This test is used to detect cracks, discontinuities, or internal deterioration in the structure of concrete.

A

ultrasonic pulse velocity test

91
Q

_____ of a concrete mixture is defined as the degree of cement hydration, which varies as a function of both time and temperature.

A

maturity

92
Q

This test (ASTM C1074) is performed on fresh concrete and continued for several days.

A

maturity test

93
Q

what are the 12 alternatives to conventional concrete?

A

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

94
Q

_____, 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).

A

self-consolidating concrete (SCC)

95
Q

Two important properties specific to SCC in its plastic state are its ______

A

flowability and stability

96
Q

VSI stands for:

A

visual stability index

97
Q

____ is a self-leveling and self-compacting, cementitious material with an unconfined compressive strength of 8.3 MPa (1200 psi) or less.

A

flowable fill

98
Q

____ 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).

A

flowable fill

99
Q

One of the unique properties of flowable fill that makes it advantageous compared with compacted granular fill is its _____.

A

flowability

100
Q

_____ is mortar or small-aggregate concrete that is sprayed at high velocity onto a surface.

A

shotcrete

101
Q

_____, 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.

A

shotcrete

102
Q

Shotcrete is applied by either the ____ or ____ process.

A

wet, dry

103
Q

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.

A

dry

104
Q

In the ____ process, all ingredients are premixed and pumped through a hose to the nozzle and forced to the surface using compressed air.

A

wet

105
Q

Generally, _____ are highly absorptive and can continue to absorb water for an extended period of time.

A

lightweight aggregates

106
Q

The specific gravity of heavyweight concrete ranges from _____.

A

3.4 to 6.5

107
Q

Concrete made with normal-weight aggregate and having compressive strength greater than _____ is considered to be high-strength concrete.

A

40 MPa (6000 psi)

108
Q

The ___ and the ____ are the controlling factors for developing high strength.

A

porosity of the cement paste, transition zone between the cement paste and the aggregate

109
Q

____ is marketed as Type K cement.

A

shrinkage-compensating cement

110
Q

____ is a mixture of aggregates and a polymer binder.

A

polymer concrete

111
Q

The addition of ____ to concrete reduces the workability.

A

fibers

112
Q

This material uses a relatively low cement factor, rather than strength.

A

roller-compacted concrete

113
Q

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.

A

high-performance concrete

114
Q

____ has been developed that is specifically designed to allow water to pass through it.

A

pervious concrete

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