Study Questions

Front 1

Why is concrete with low absorption needed for architectural panels exposed to the weather?

Back 1

To minimize staining caused by weathering

Front 2

What is the batch deviation for fine aggregates

Back 2

Plus or minus 2 percent

Front 3

Which types of cements should be used for mixes requiring sulfate resistance

Back 3

TYPE II and Type V

Front 4

How can coarse aggregates affect strength?

Back 4

Larger aggregate generally means higher strength, Dirty coarse aggregates cause variations in strength

Front 5

Aggregates not passing the ____ sieve are called _____

Back 5

#4. Coarse

Front 6

Which cement compound hydrates slowly, contributes to later strength gain, and produces less heat of hydration?

Back 6

C2s

Front 7

For normal weight concrete, pulse velocities above _____ ft per second generally indicate a good quality of concrete

Back 7

12,000 ft per second

Front 8

Steel conforming to ASTM A36 does not require preheating unless the steel is thicker than ______ in.

Back 8

3/4"

Front 9

What is the common tolerance for hold down location along the length of a prestressed member?

Back 9

+/- 20 inches

Front 10

For architectural concrete MNL 117 requires that ____ test specimens be made for each mix or for each 40 cubic yards of any mix?

Back 10

4

Front 11

How much water is needed to fully hydrate a pound of cement?

Back 11

0.25 lb

Front 12

The air content of concrete that is made with a given amount of air entraining admixture will be _____ if the concrete is cool when mixed than if the concrete is warm.

Back 12

Higher

Front 13

How many times can electrodes be redried?

Back 13

1 time

Front 14

Cements with large amounts of ______ are more susceptible to sulfate attack, particularly in concrete with higher water to cement ratios?

Back 14

C3A

Front 15

Define the consistency of plastic concrete?

Back 15

The ability of the concrete to flow into the forms and be compacted and finished

Front 16

Describe bleeding and how it is normally handled?

Back 16

Bleeding is caused by settlement of solid particles in consolidated fresh concrete displacing water, so water appears at the surface. Normally bleed water evaporates, but if it does not evaporate it must be removed before finishing the surface.

Front 17

Define Blaine

Back 17

Blaine refers to the fineness of cement as measured by the Blaine air permeability method.

Front 18

According to ASTM c31, what is the maximum permissible size of coarse aggregate that can be used in 6x12 test cylinders?

Back 18

2"

Front 19

Which 2 chemical compounds in cement produce the most heat?

Back 19

C3S & C3A

Front 20

What is the usual dosage of silica fume content by cement weight?

Back 20

5-10%

Front 21

Super-plasticized concrete may have a ______ texture, and toweling may be difficult

Back 21

Sticky

Front 22

What length crack is permissible in a fillet weld?

Back 22

No cracks are permitted

Front 23

According to ACI 318-95, what type of cement should be used in prestressed concrete piles that are to be exposed to sea water?

Back 23

TYPE II

Front 24

What is the maximum water soluble chloride ion content in prestressed concrete products?

Back 24

0.6%

Front 25

How many release cylinders must be tested?

Back 25

2

Front 26

Describe a situation where increasing the slump may not increase workability?

Back 26

Increasing the slump by adding water may cause segregation

Front 27

True or false, C4AF contributes little to strength gain or heat of hydration?

Back 27

True

Front 28

Which type of portland cement possesses the highest Blaine fineness?

Back 28

Type III

Front 29

Cement containing lumps probably has?

Back 29

High values of loss on ignition

Front 30

In Portland cement, what is the limit of insoluble residue?

Back 30

.75%

Front 31

How is consistency measured?

Back 31

By the slump test

Front 32

What is the tolerance for the location of individual strands in a double tee

Back 32

+/- 1/4"

Front 33

What is the maximum permissible stress that can be applied to prestressing strands during jacking?

Back 33

80% of the tensile strength of the strand.

Front 34

Silica fume concrete does not _____?

Back 34

Bleed

Front 35

What problem can occur with high carbon equivalent welding?

Back 35

The weld becomes brittle

Front 36

Steel becomes _____ if it is cold when welded?

Back 36

Brittle

Front 37

What is the batch deviation for cement?

Back 37

+/- 1%

Front 38

What is the most commonly used corrosion inhibitor?

Back 38

Calcium nitrite

Front 39

What two items require closer control for lightweight concrete mixes than normal weight concrete mixes?

Back 39

Moisture content of aggregates

Unit weight of fresh concrete

Front 40

True or false, Calcium Nitrite is an accelerator as well as a corrosion inhibitor?

Back 40

True

Front 41

What is the batch deviation for admixtures?

Back 41

+/- 3%

Front 42

What is the batch deviation for water?

Back 42

+/- 1.5 %

Front 43

True or false, pozzolans reduce the amount of entrained air in concrete?

Back 43

True

Front 44

What size tamping rod is used for rodding 4x8 cylinders?

Back 44

3/8" diameter, 12" long with hemispherical end

Front 45

Cements with large amounts of this compound _______ are more susceptible to sulfate attack, particularly in concrete with high water-cement ratios?

Back 45

C3A

Front 46

List four common mistakes in performing slump tests.

Back 46

1. Failure to perform the test on a rigid, non absorptive level surface

2. Failure to fill the slump cone in three equal volume layers

3. Failure to measure the slump to the displaced original center of the top surface

4. Failure to raise the cone 3-7 seconds.

Front 47

Large amounts of which compound increases early strengths but causes late strengths to be lower than normal?

Back 47

C3A

Front 48

Define the components of sand-lightweight concrete, and what unit weights are normally obtained with these mixes?

Back 48

Made with lightweight coarse aggregate and normal weight sand. Unit weight range is about 110-125 PCF

Front 49

The average diameter of a cement particle is about _____ times as great as that of an average silica fume particle?

Back 49

100 times

Front 50

What property of concrete is measured by a split cylinder test?

Back 50

Splitting tensile strength

Front 51

Define type I cement

Back 51

Normal portland cement

Front 52

How does air content affect slump?

Back 52

Increase in air will generally result in an increase in slump

Front 53

E70XX electrodes not used within 4 hours must be ______ before use

Back 53

Redried

Front 54

Define Vicat?

Back 54

Vicat refers to the setting time of cement paste as measured using the Vicat apparatus

Front 55

HRWR's reduce water demand by _____ to ______ %?

Back 55

12-30 %

Front 56

List 7 procedures that can be used to minimize plastic shrinkage cracking

Back 56

1. Use fresh cool concrete

2. Shield from wind

3. Cool forms

4. Use fog sprays near forms

5. Use fibers

6. Cover as soon as possible

7. Use evaporation retardant

Front 57

Why should air entrainment be considered in mixes that are not exposed to weather? 2 reasons!

Back 57

1. To improve workability

2. Reduce bleeding of the concrete

Front 58

Electrodes conforming to AWS.A5.1 must be stored in ovens of atleast ________ after removal from the sealed containers?

Back 58

250 degrees F.

Front 59

Which of the following can cause discoloration of concrete surfaces?

4 reasons!

Back 59

1. Variable W/CM ratios

2. Form oils

3. Hot spots during heat curing

4. Variations in slump.

Front 60

Which test method is specifically used to determine the presence of staining materials in lightweight aggregates?

Back 60

ASTM C641

Front 61

Describe the standard test method to assure the uniformity of mixed concrete?

Back 61

1. Take samples from two locations of a concrete batch, such as after 10% has been discharged and after 80 percent has been discharged.

2. Measure unit weight, air, slump, coarse aggregate content, unit weight of air free mortar, compressive strength at 7 days and compare the results.

3. If they are within the tolerances of ASTM C94, the concrete uniformity is satisfactory.

Front 62

Organic materials in concrete aggregate will affect the _____ and _____ ?

Back 62

Setting time and air content

Front 63

What is the batch deviation for coarse aggregate?

Back 63

+/- 2 %

Front 64

What is the main function of cement compound C4AF?

Back 64

Use up excess alumina to reduce the amount of C3A in the cement.

Front 65

List 6 different methods for estimating compressive strength if concrete in lieu of 6x12 cylinder tests?

Back 65

1. Impact rebound hammer

2. Windsor probe

3. Pulse velocity

4. 4x8 cylinder tests

5. Pull out strength of hardened concrete

6. Cores or prisms

Front 66

ASTM states that test cylinders be loaded at a rate of _______ PSI +/- ______ PSI per second?

Back 66

35 psi +/- 15 psi

Front 67

The preheated area of A36 steel must extend _______ inches in all directions from the weld?

Back 67

3 inches

Front 68

True or false, air entrainment generally decreases the permeability of concrete?

Back 68

True

Front 69

What is the permissible rate of load application In pounds per second for a 4x8 cylinder?

Back 69

250-625

Front 70

E90xx electrodes may not be out of their containers or ovens for more than _______

Back 70

1 hour

Front 71

Define the range of unit weight for structural lightweight concrete?

Back 71

90-130

Front 72

Concrete made with both lightweight coarse and fine aggregate is called?

Back 72

All lightweight

Front 73

Typically white cement compounds have high C2S amounts. What effects will this have on strength gain properties?

Back 73

Slow strength gain unless cement has high fineness

Front 74

True or false, drying shrinkage of super-plasticized concrete is about 30% less than that of normal concrete?

Back 74

False. This is not a true statement

Front 75

MGO content in cement must be less than ______ %

Back 75

6.0 %

Front 76

Insoluble residue in cement must not exceed ______ %

Back 76

.75%

Front 77

The C3A content of type II cement must not exceed _____ %

Back 77

8%

Front 78

Sulfur trioxide SO3 is limited to ____ % for type I and II cements?

Back 78

3%

Front 79

Large amounts of _______, while increasing early strengths will cause late strengths to be lower than normal.

Back 79

C3A

Front 80

Which two different methods are used to determine cement fineness?

Back 80

1. Blaine air permeability test

2. Wagner turbidemeter test

Front 81

ASTM C150 requires that the initial setting time of cement be atleast _____ minutes Vicat or _____ minutes Gillmore.

Back 81

45 Vicat

60 Gillmore

Front 82

ASTM C150 requires that the FINAL setting time of cement be no longer than _____ minutes Vicat and ______ minutes Gillmore.

Back 82

1. 375 minutes Vicate

2. 600 minutes Gillmore

Front 83

What concrete properties are affected significantly by the gradation of fine aggregates?

4 answers

Back 83

1. Water demand

2. Bleeding

3. Workability

4. Finishability

Front 84

Define Autoclave expansion

Back 84

Rapid method of determining if cement is unsound. Autoclave expansion is limited to 80%

Front 85

Name 5 of the effects of a higher W/CM ratio of the concrete produced.

Back 85

1. Lower strength

2. Concrete will be MORE permeable

3. Concrete will be less resistant to abrasion

4. Concrete MAY be less durable

5. Concrete will be less sulfate resistant

Front 86

Name 5 items that affect consistency

Back 86

1. Amount of water

2. Air content

3. Concrete temperature

4. Admixtures

5. Shape, texture and gradation of aggregates

Front 87

When the base metal is below 32 f. The metal shall be preheated to atleast ______ or above. And to be maintained at this minimum temperature during welding

Back 87

70 degrees F.

Front 88

Which electrodes must be used with ASTM A706 bars

Back 88

E80XX

Front 89

If bars of different grades are welded together which electrodes must be used?

Back 89

Electrodes matching the lower strength bars.

Front 90

Define type II cement

Back 90

Used in concrete where:

1. Moderate sulfate resistance

2. Reduced heat of hydration is desired

Front 91

What problems can occur because of excessive fineness in aggregates

Back 91

1. Concrete can be sticky

2. Concrete can be prone to plastic shrinkage cracking

3. Concrete strength can be lowered

Front 92

List 2 precautions that should be observed of welding galvanized steel.

Back 92

1. Provide adequate ventilation to dissipate noxious fumes during welding

2. Avoid zinc penetration into welds

Front 93

Welds should be free of

Back 93

Overlap

Front 94

Describe autoclave expansion

Back 94

A rapid method of determining if cement is unsound

Front 95

What preheat temperature is required for CE'S over .75%

Back 95

100 degrees farenheit

Front 96

No. 7 to no. 11 bars must be preheated if the carbon equivalent is _______ or higher?

Back 96

.46%

Front 97

In the event of low concrete cylinder strengths the average of 3 cores must be ______ with no single core less than ______ of specified concrete strength.

Back 97

85% & 75%

Front 98

How many drum revolutions for truck mixed concrete are required to fully mix concrete?

Back 98

70-100 revolutions

Front 99

How many revolutions must truck mixed concrete revolve after adding water?

Back 99

30 revolutions

Front 100

Water reducers reduce the water demand from ______ to ______.

Back 100

5-10%

Front 101

Name three uses for high range water reducers?

Back 101

1. Reduce water

2. Accelerate strength gain

3. Lower heat needed for curing.

Front 102

What is the maximum under-cutting for welding reinforcing bars?

Back 102

1/32 of an inch maximum except at raised bar deformation where 1/16 " is allowed.

Front 103

Which electrodes are satisfactory for welding grade 60 rebars to ASTM A36 steel?

Back 103

E90XX electrodes

Front 104

Which electrodes must be used with grade 40 bars?

Back 104

E70XX

Front 105

List 3 advantages for using 4x8 cylinders opposed to 6x12 inch?

Back 105

1. Reduced size and weight

2. Reduced storage capacity needed.

3. Lower capacity testing machine is needed.

Front 106

Welding should not be done when the ambient temperature is lower than ______.

Back 106

0 degrees F.

Front 107

What is the tolerance for comparing measured strand load and elongation with the calculated theoretical strand load and elongation?

Back 107

5%

Front 108

To reduce or eliminate the potential for efflorescence consider the following 5 things?

Back 108

1. Use low alkali cement,

total alkali content should be limited to less than .35% of NA2O.

2. Never use unwashed sand containing soluble alkali sulfates.

3. Use clean mixing water. Free from harmful amounts of acids, alkali, organic materials, minerals and salts.

4. Additions of 5-10% silica fume can produce large decreases in permeability and alkali content in the pore structure.

5. Reduce concrete permeability. Use concrete with low water absorption.

Front 109

List 5 reasons for preforming pulse velocity tests of concrete?

Back 109

1. Asses uniformity and relative quality of concrete.

2. Indicate presence of voids or cracks

3. Estimate depth of cracks.

4. Indicate changes in the properties of concrete.

5. Estimate the severity of deterioration or cracking of concrete.

Front 110

What methods are used to control friction losses at hold down, and hold up devices? 4 methods as followed

Back 110

1. Stress strands at both ends of bed.

2. Use rollers at each hold-down and hold-up.

3. Depress or raised strands starting at the central hold-down or hold-up in the casting bed, and proceed symmetrically about this location.

4. Apply vibration the strands as they are being stressed.

Front 111

What is secondary efflorescence?

Back 111

Secondary efflorescence is due to an outside source of water

ie, rain, or condensation saturating the water the concrete and pulling the calcium hydroxide to the surface to react with carbon dioxide. It is not possible to make a clear distinction between primary and secondary efflorescence, because the transition between the two is not clear cut.

Front 112

Which 8 factors increase concretes ability to resist water penetration?

Back 112

1. Low W/CM ratio

2. Use of silica fume

3. Adequate curing

4. Well graded mix

5. Good compaction

6. Minimized cracking

7. Good joints

8. Coatings

Front 113

What 2 key factors can a producer influence to minimize efflorescence?

Back 113

1. Reduce concrete permeability

2. Use a concrete with low water absorption specifically 5-6 % by weight or 12-14% by volume.

Front 114

Which 3 properties of stainless steel differ from those of carbon or other steels?

Back 114

1. Thermal conductivity is much lower so they are more susceptible to local over heating or distortion when they are welded.

2. Thermal expansion is higher and this tends to increse distortion and result in higher stresses on the weld during cooling.

3. Resist oxidation until heated temperatures around their melting points in the presence of air.

Front 115

List 2 methods for developing correlation curves?

Back 115

1. Plot the data and draw by eye a best fit line.

2. Preform a linear regression analysis.

Front 116

What are the two methods of installing deflected strands?

Back 116

1. Stress the strands in their final posistion.

2. Partially stress the strands in a straight posistion or partly deflected posistion and then raise or lower the strands to their final posistion.

Front 117

Define the optimum sand ratio.

Back 117

For a given set of materials and for a given W/CM ratio, the optimum sand ratio is the percent of sand of the total aggregate weight at which the water content and the cement content are at a minimum.

Front 118

What 4 conditions must be present for efflorescence to occur?

Back 118

1. Soluble substances must be in 1 or more of the materials.

2. Moisture must be present to dissolve the substances

3. Evaporation, hydrostatic, or osmotic pressure must cause the solution to move towards the surface.

4. The solution must evaporate to leave these substances behind as efflorescence.

Front 119

Relatively insoluble efflorescence deposits may indicate which 2 problems?

Back 119

1. Problems related to too much moisture movement into the concrete.

2. Unfavorable curing conditions.

Front 120

What 3 ways can efflorescence be identified?

Back 120

1. Petrographic analysis

2. Chemical analysis

3. X-RAY diffraction analysis

Front 121

What is primary efflorescence?

Back 121

A substance on the surface of concrete that appears as a whitish deposit and is caused by calcium hydroxide produced by the hydration reaction between cement and water dissolving in the mixing water. And migrating to the surface of the fresh concrete where it reacts with carbon dioxide in the air to form water insoluble calcium carbonate.

Front 122

What is the recommended sequence of depressing or rasing strands when strands are partly tensioned before they are deflected.

Back 122

Preferably depressed at all hold down or hold up locations simultaneously. If that is not feasible, depress or raise at center hold down or hold up then depress or raise at other locations symmetrically along the bed.

Front 123

Describe a role of thumb that is useful in adjustment of lightweight concrete trial mixes?

Back 123

A change in cement content of 1 PCY required a change in the dry loose volume of aggregate of about .01 cubic foot in the opposite direction.

Front 124

What is meant by preheat temperature?

Back 124

It is the temperature to which steel must be heated prior to welding these temperatures depend on the bar size and carbon equivalence and are specified in AWS.4-92