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CIVI 321 > Durability > Flashcards

Durability Flashcards

1
Q

What is deterioration?

A
  • Physical Manifestation of failure of a material (craking, spalling, delamination, pitting)
  • Decomposition of material (disintegration, weathering)
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2
Q

What are the causes of deterioration?

A
  • Interaction with environment (external)

- Interaction between constituents (internal)

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3
Q

What are the three types of concrete deterioration?

A
  • Physical Det.
  • Chemical Det.
  • Reinforcement Corrosion
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4
Q

What causes physical deteriorations?

A
  • Frost
  • Cracking
  • Fire
  • Abrasion
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5
Q

What causes chemical deteriorations?

A
  • Sulphate
  • Sea Water
  • Leaching
  • AAR
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6
Q

What causes reinforcement corrosion?

A
  • Carbonation

- Chlorides

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7
Q

What is corrosion?

A

Conversion of IRON to IRON OXIDE (rust)

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8
Q

What are the consequences of corrosion?

A
  1. rust
  2. expansion
  3. stress
  4. cracking
  5. spalling
  6. more rust
  7. less steel to take the load
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9
Q

What does it mean when reinforcement are passivated?

A

Covered by thin oxide film

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10
Q

What are the most common causes of depassivation?

A
  • Ingress of chloride ions

- Carbonation of concrete

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11
Q

To fight corrosion, what are they using?

A
  • Epoxy coated bars
  • Stainless steel rebar
  • FRP rebar
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12
Q

What are the steps to repair concrete deterioration?

A
  • Concept
  • Surface preparation
  • Cleaning Reinforcement
  • Corrosion Inhibitor
  • Bond Coat
  • Polymer Mortar (coarse)
  • Polymer Mortar (fine)
  • Anti-Carbonation Coat
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13
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
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14
Q

What are the signs of Freeze/Thaw Damage?

A
  • Spalling
  • Paste Failure: Fracture surface consist of broken paste and occasionally undisturbed aggregate faces.
  • Aggregate failure: spalled section contains a broken aggregate at the bottom of fracture surface pit
  • Paste Fractures due to aggregate expansion
  • D-Cracking and Scalling: Often occurs at expansion joints
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15
Q

How to protect concrete?

A
  • Keep concrete dry (not always possible)
  • Reduce the amount of freezable water (by reducing capillary porosity, feasible)
  • Provide a relief for pressure (air entrainment)
  • Combination of the above
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16
Q

Explain air entrainment.

A
  • Network of air bubbles
  • Using a chemical admixture mixed with concrete
  • Size usually 10um to 100um
  • Dosage, type of cement, compatibility with other admixtures used can influence volume and spacing of air bubbles
17
Q

What is an Alkali-Aggregate Reaction in concrete?

A

AAR correspond to chemical reactions between alkalis (Na2O & K2O) in the concrete pore fluid and some mineral phases in the aggregates.

18
Q

Alkalis are supplied to the concrete pore fluid from sources such as?

A
  • Cement
  • Chemical Additives
  • Aggregates (medium to long-term)
  • Supplementary cementing materials
  • Sea Water
  • De-icing Salts
19
Q

Explain Alkali-Silica Reaction (ASR)

A

Alkali hydroxide+Reactive silica gel = Alkali Silica Gel

Alkali silica gel filling microcracks+Moisture = expansion

20
Q

Time for distress due to AAR

A
  • less than 5 to more than 25 years
  • Type and reactivity level of the aggregate
  • Alkali content and design of the concrete mixture
  • Exposure conditions
21
Q

What are the field symptoms of ASR?

A
  • ASR induced longitudinal Cracking in soffit of bridge deck
  • Longitudinal cracking in RC column
22
Q

What are the field symptoms of AAR?

A
  • Map cracking pattern

- Oriented cracking bridge columns

23
Q

Preventive measures against AAR?

A
  • Use a non-reactive aggregate
  • Selective quarrying & aggregate beneficiation
  • Limit the alkali content of the concrete mixture: use a low-alkali cement or limit alkali content of concrete
  • Use an adequate proportion of supplementary cementing material (SCMs)
24
Q

What is meant by Hydrates?

A

Chemical reactions between cement and water

Cement+Water = Hydration products (CSH, CH)+Heat

25
Q

How to reduce sulfate attack?

A
  • Type 2: Moderate Sulfate Resistance (Lower C3A, 7.5%)
  • Type 5: High Sulfate Resistance (Lower C3A, 3.5%)
  • Addition of SCMs
26
Q

What is the purpose of SCMs?

A
  • Enhancement to mechanical properties and durability
  • Refinement of porosity
  • Densification of aggregate-cement paste interface
27
Q

Explain Plastic and Drying Shrinkage.

A
  • Very rapid loss of moisture while concrete still plastic
28
Q

What are the factors that control Plastic and Drying shrinkage?

A
  • Concrete and air temperature
  • Relative Humidity
  • Wind Velocity
29
Q

What solution can be done to prevent plastic and drying shrinkage?

A
  • Keep water-cement ratio low

- Prevent rapid moisture loss: wet curing, wind break and shade concrete surface

30
Q

What are the thermal effects on concrete?

A
  • Thermal exp/contraction
  • Uneven thermal loads
  • Restraint to volume change
  • Early thermal cracking of concrete
  • Thermal movement in existing cracks

CIVI 321 (7 decks)

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