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CIVI 321 > Durability > Flashcards

Durability Flashcards

1
Q

What is the objective of durability?

A

To design and build concrete structures that meet their
Expected Service Lives with Minimum Repair

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2
Q

What is deterioration?

A

Physical manifestation of failure of a material (e.g., cracking, spalling, delamination, pitting)
Decomposition of material (disintegration, weathering)

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3
Q

WHAT ARE THE CAUSE OF CONCRETE DETERIORATION?

A

PHYSICAL DETERIORATION
CHEMICAL DETERIORATION
REINFORCEMENT CORROSION

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4
Q

What causes PHYSICAL DETERIORATION?

A

Frost
Cracking
Fire
Abrasion

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5
Q

What causes CHEMICAL DETERIORATION?

A

Sulphate
AAR
Sea water
Leaching

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6
Q

What are the causes REINFORCEMENT CORROSION?

A

Chlorides
Carbonation

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7
Q

How much of steel produced annually in the world is used to repair corrosion prob?

A

40% (25% to 30% for corrosion within reinforced conrete)

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8
Q

What is corrosion?

A

it is a cycle caused by iron oxyde (rust) that expands the concrete –>cause stress–> causes failure —> causes spalling of concrete (écaillage) –>causes more rust (cycle goes back to expansion)

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9
Q

What is passivation?

A

thin oxide film on reinforcement

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10
Q

What causes de-passivation?

A

Entering of chlorides ION
Carbonation of concrete

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11
Q

How much can volume increase with rust?

A

Up to 6 times

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12
Q

How to differentiate carbonation from chloride infiltration?

A

Phenolphthalein test

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13
Q

Phenolphthalein test –>PINK

A

NOT CARBONATED/Chloride infiltration

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14
Q

Phenolphthalein test–> not pink

A

Carbonated

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15
Q

What is the diffusion coeff?

A

rate of chloride ingress

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16
Q

how to reduce diffusion coeff?

A

by reducing voids–>reducing permeability–>reducing water–>reducing diffusion coeff?

17
Q

What to use to reduce corrosion?

A

Epoxy coated bars (if defected in coat, it can accelerate the corrosion affect (concentrated in one pts))
Stainless Steel rebar ($$$)
FRP rebar (brittle)

18
Q

How to repair corrosion affected concrete?

A

Remove concrete–>corrosion inhibitors (adm) –> cover concrete –> coating–> impregnation
some cases, replace reinforcement/add new

19
Q

How much water expands as it freezes?

A

Expands up to 9% (tensile stress)

20
Q

What are the most common signs of freeze/thaw deterioration?

A

-Development of cracks sub-parallel to the surface
-Cracks throughout the concrete (delamination)
-Gaps around aggregates in the surface regions of concrete.

21
Q

How much freeze&froze cycle can concrete resists?

A

300 cycles before damages

22
Q

What is paste failure? (spalling)

A

Paste failure: Fracture surface consists of broken paste and occasionally undisturbed agg. faces

23
Q

What is agg. failure? (spalling)

A

spalled section contains a broken agg. at the bottom of fracture surface pit

24
Q

in sidewalks, where does D-cracking and scaling occurs bc of freeze-thaw?

A

expansion joints

25
Q

How to protect concrete from F-t?

A

keep concrete dry (not always possible)
Reduce amt of freezable water
Provide a relief for pressure (AEA)
Combination of above

26
Q

Where does the Alkali in AAR comes from?

A

from cement

27
Q

Where does the silica in ASR comes from?

A

Agg (silica mineral)

28
Q

ACR or ASR worst?

A

ACR is worst (alkali carbonate reaction)
Avoid it by using agg in Kingston (limestone)

29
Q

What are the field symptoms of ASR?

A

Longitudinal cracking
Cracks starts from the 1st layer of agg
Map cracking
White powder (silica gel extracted from concrete)

30
Q

How to prevent AAR (ASR & ACR)

A

use non reactive agg (100% for ACR)
selective aff
Limit alkali in cement & concrete
Lithium adm (earlier apply –> less damage)
use SCM (SF, FA, Slag)
Tight the concrete (confinement–>increase strength of struc; NOT permanent)

31
Q

How is the sulfate dangerous?

A

Sulfate is aggressive with water/moisture bc attack hydration product for cement

32
Q

Hydration products; what are the others?

A

Ettringite —> Monosulfate (stable phase of ettiringite)

33
Q

How is ettringite and monosulfate created?

A

C3A + gypsum+water =ettringite (unstable)
C3A+ettringite+water = monosulfate (stable)
Volume ett> volume mono (about 700times)

34
Q

How can monosulfate go back to ettringite?

A

CH+sodium sulfate= GYPSUM +sodium hydroxide
GYPSUM +monosulfate +Water= ettringite

35
Q

WHY is it a problem the conversion of ettringite to monosulfate?

A

Very large volume expansion and contraction

36
Q

How to prevent sulfate attacks?

A

prevent with type 20 and type 50 cement (low C3A)
adding SCM (CH to CSH; pozzolanic activity)

37
Q

How to prevent plastic and drying shrinkage?

A

Wet curing
Wind break
Shade concrete surface

38
Q

What causes Drying shrinkage?

A

By volume change (decrease) due to loss of moisture in combination with restraint of soil or structure (struc applies stress by stoping mvt)
Thermal effects(expansion)

39
Q

How to control shrinkage in sidewalks?

A

Seperation because of agg. that will restrain the slab
(limit cracking)

CIVI 321 (13 decks)

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