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CE materials > Exam 2 Vocab > Flashcards

Exam 2 Vocab Flashcards

1
Q

What does paste consist of

A

Air, water, cementitious materials

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2
Q

What does mortar consist of?

A

Paste and fine agg.

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3
Q

What does concrete consist of?

A

Coarse agg., and mortar (air, water, cement materials, and Fine agg.)

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4
Q

What is workability

A

How easy or difficult it is to place in forms, consolidate and to finish.

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5
Q

What does an air entraining agent do.

A

Adds microscopic air bubbles, protects concrete from freeze thaw, increases slump (more stiff)

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6
Q

A larger w/c ratio means what

A

It has more water and has less compressive strength

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7
Q

Concrete with more of its volume coarse agg will have a higher or lower bulk volume fraction (b/b0)

A

Higher

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8
Q

Advantages of concrete over steel

A

More readily available, cheaper

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9
Q

Disadvantages of concrete?

A

Low tensile strength(needs reinforcement for tension), Low ductility (cannot withstand large deformations before failure), Instability in volume (expands and shrinks), Low strength to weight ratio

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10
Q

What is Portland cement composed of

A

Ground clinker and gypsum

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11
Q

C3S

A

Tricalcium silicate, Primary strength in portland cement, moderate rate in strength gain, gives off high heat

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12
Q

C2S

A

Dicalcium silicate, gives some strength, Slow rate of strength gain, gives off low heat

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13
Q

C3A

A

Tricalcium aluminate, “bad guy”, Gives no strength, Very fast rxn, Gives off very high heat

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14
Q

C4FA

A

Iron, turns grey, no strength

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15
Q

Gypsum

A

Primary prevent C3A from reacting, gives no strength

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16
Q

Type 1 cement

A

General use anywhere that theres not specific requirements. Ex. highways, inland bridges, floors and buildings

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17
Q

Type III cement

A

Same as Type one but finer so it reacts faster (sets faster). Uses - Precast concrete, cold weather paving, paving to minimize traffic stoppage

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18
Q

Type IV

A

Reduced amounts of C3S and C3A, Low heat and slow strength gain, Moderate resistance to sulfate. Used for Mass concrete pours (dams, large concrete)

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19
Q

Type V

A

Lower amounts of C3A than Type 4, High!! resistance to sulfate attacks, used on ocean

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20
Q

Type II

A

Reduced C3A, Moderate resistance to sulfate. Low heat from rxns, used in high sulfate soils

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21
Q

What are the five most important compounds in portland cement

A

C3S, C2S, Iron, C3A, Gypsum

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22
Q

Important rxn products

A

CSH (calcium silicate hydrate), CH (Calcium hydroxide, Sulfoaluminates (all bad)

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23
Q

CSH

A

Calcium silicate hydrate, “glue” primary strength of hydrated cement

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24
Q

CH

A

Calcium hydroxide, flat hexagon crystals, water soluble, High pH

25
Q

Ettringite

A

Hexagon needle like shape, reduced workability. Too much of this causes “False set”

26
Q

Monosulfoaluminates (MSA)

A

Cluster of irregular plates “rosettes” Vulnerable to sulfate attacks

27
Q

What is causes by too little gypsum

A

Flash Set, Sets too fast creates alot of heat

28
Q

What is caused by too much gypsum

A

Setting delayed too long

29
Q

Stage 1 of hydration

A

First contact of cement and water, initial hydration products form around C3S and the process slows

30
Q

Stage 2 of hydration

A

Cement remains workable for hours. concrete is places in forms and consolidated (vibrated)

31
Q

Stage 3 of hydration

A

CSH begins forming around C3S, ettringite forms “initial set” water can not longer easily reach C3S, DIFFUSION CONTROLLED

32
Q

Stage 4 of hydration

A

CSH continues to get thicker around C3S and rxns become slowS

33
Q

Stage 5 pf hydration

A

Hydration nearly complete

34
Q

What kind of water can be used in concrete

A

If its good enough to drink it can be used

35
Q

Air entraining admixtures

A

Freeze thaw resistance, used in saturated concrete, bubbles in concretes, increased air content, reduced strength

36
Q

Water reducing admixtures (as water reducer) Given ( Same cement, less water)

A

Same slump, lower w/c, f’c increases

37
Q

What does set retarding admixtures do?

A

Slows down set times to remain workable for longer

38
Q

What do mineral admixtures do?

A

Replace cement with waste products such as pozzolans. reduces cement used and improve durability

39
Q

Types of pozzolans

A

Fly ash, silica fumes.

40
Q

Mineral admixtures effect on hardened concrete

A

reduces porosity, and has higher strength later on

41
Q

Why is silica fumes added to concrete?

A

Creates more CSH to increase compressive strength and reduces porosity

42
Q

What is durability

A

the ability to resist weathering, chemical attack, and abrasion

43
Q

What are deterioration mechanisms of concrete

A

ASR, chemical attacks (sulfate, seawater, acids), corrosion from rebar, freeze and thawing

44
Q

What does a high w/c ratio do to permability

A

increases, more capillary pores

45
Q

What does a sulfate attack do?

A

rxn of MSA, expansion causes cracking

46
Q

How to control sulfate attack?

A

Use low C3A cement, add pozzolan or slag, use a lower w/c to reduce permeability

47
Q

What does ASR do? and how to avoid it?

A

forms a gel that expands in the concrete. Use a blend of agg. to reduce amount of reactive silica

48
Q

Limit distance concrete can fall,

A

3 to 5 feet

49
Q

What is Rheology

A

The science of flowability

50
Q

What is Thixotrophy

A

A property of becoming fluid when shaken and returning to a semisolid when standing

51
Q

Factors to concrete segregation

A

Larger agg., mixes is way to wet or way to dry

52
Q

What is bleeding

A

Upward movement of water after the concrete is consolidated, has a negative effect of strength and ductility

53
Q

How to reduce bleeding

A

Increase fineness, increase hydration (air entrained), reduce water content

54
Q

What does too much coarse agg cause

A

A harsh mix (less workability)

55
Q

What does too much fine agg cause?

A

Oversanded mix, permable, more workable

56
Q

What is initial set

A

Begining of stiffening can no longer be molded

57
Q

What is final set

A

When the cement has hardened some and can sustain load

58
Q

What is false set

A

Formation of ettringite soon after mixing but can still be restored to a fluid

59
Q

What is flash set

A

Occurs from C3A forming large amounts of MSA. Sets too fast cannot be reversed

CE materials (6 decks)

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