T3-5: Prognosis for the Structure Flashcards

1
Q

What are five key things to determine in the evaluation of a concrete structure?

A
  • Deterioration mechanisms
  • Causes of deterioration
  • Likely future performance
  • Repair possibilities
  • Extent of repair
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2
Q

What does the assessment of carbonation entail (x2)?

A
  • Assessment of residual life
  • Carbonation and cover depth analysis
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3
Q

What does this equation represent?

A

Carbonation depth

NB. equation assumes that the rate of advance of the carbonation front is diffusion controlled

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4
Q

[NAQ] example carbonation predictions

A
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5
Q

[NAQ] carbonation depth vs age of structure graph

A
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6
Q

Why are histograms of carbonation and cover depth frequency superimposed?

A

Because any overlap can be assessed, and a probability of corrosion estimated

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7
Q

Does higher rainfall lead to more/less/no difference in terms of carbonation rate?

A

Less
- e.g. outside surface of structures
- excessive moisture (saturation) blocks pores; slowing carbonation
- if very dry, also leads to slower carbonation; not enough moisture for chemical reactions to occur

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8
Q

Describe the programme of the assessment of chloride profiles (x6 steps)

A
  1. Best-fit curve through points
  2. Establish surface chloride concentration
  3. Establish background chloride concentration
  4. Establish chloride diffusion coefficient
  5. Calculate chloride profiles at different ages
  6. Determine when initiation concentration reaches reinforcement
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9
Q

What does this equation represent?

A

It is the chloride diffusion modelled in accordance with Flick’s 2nd law

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10
Q

[NAQ] graph(s) showing chloride content results/ chloride prediction

A
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11
Q

What method is used to measure corrosion rate?

A

Linear polarisation resistance
- measures corrosion rates by analysing the relationship between the potential and current generated between electrodes in a corrosive environment
- embedded probes in the concrete
- demountable devices

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12
Q

[NAQ] sketches showing process of measuring corrosion rate

A
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13
Q

For modelling corrosion rate from linear polarisation resistance, what needs to be assumed?

A

A typical corrosion current, based on prevailing environmental conditions

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14
Q

Name different sensors/ methods used for monitoring a structure (x11)

A
  • Embedded half-cells
  • Resistivity probes
  • Corrosion probes
  • Linear polarisation
  • Precipitation detectors
  • Internal relative humidity (RH) probes
  • Temperature sensors
  • Impact/deflection sensors
  • Crack movement
  • Tilt/lean sensors
  • Video surveillance
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15
Q

What problem can occur that can make at-risk areas not visible?

A

Half-joint issues

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16
Q

Describe half-joint issues

A
  • Arise from moisture accumulation, and corrosion of reinforcement, leading to concrete deterioration
  • Concealed bearing
  • At-risk areas not visible
  • Corrosion risk masked by uncorroded steel
  • Sampling is complicated by congested reinforcement layout
  • Joint area becomes a salt trap
  • Deteriorated state needs to be reassessed
17
Q

Which of these bridge deck support arrangements (half-joints) is likely to cause the biggest and smallest maintenance challenge?

A

Most = A:
- No physical access for inspection or maintenance of the bearing shelf
- High risk of hidden deterioration

Least = D:
- Clear access to bearings and half-joint zones

18
Q

Name different types (x8) of issues with half joint inspection

A
  • Poor inspectability
  • Movement joint failure
  • Salt water build up
  • Coastal exposure
  • Corrosion risk
  • Winter maintenance
  • Concrete protection
  • Corrosion fuels
19
Q

What is a hidden defect in asphaltic plug joints?

A

May conceal substantial leakage beneath

20
Q

What are half-joint issues/ hidden defects, shown by I-R optic endoscope viewers (x2)?

A
  • Salt water build-up
  • Active corrosion
21
Q

As well as I-R fibre-optic endoscope viewers, what are three other inspection methods

A
  1. Long, directional cores (Ferroscan/radar)
    - half-cell “down the hole” surveys
  2. EMR corrosion excitation surveys
  3. Sonic pulses (shown)
    - e.g. the Doktor equipment
    - acoustic emission
    - embedded monitoring probes
    - re-analysis in corroded weakened state
22
Q

Name one thing that can be done to minimise risk of half-joint issues

A

Install a surface protection system to stop chloride from getting into the concrete

23
Q

[NAQ] post-tensioned bridge beams sketches, showing leakage path, gap in duct and trapped air pocket

24
Q

Name different types (x8) of issues with duct inspection

A
  • Poor inspectability
  • Movement joint failure
  • Salt water build up
  • Coastal exposure
  • Corrosion risk
  • Winter maintenance
  • Concrete protection
  • Corrosion fuels
25
Q

What methods (x3) are used for location of ducts?

A
  • Impulse radar
  • X-ray
  • Metal detectors (rarely successful)
26
Q

What is done to access and expose ducts?

A

Coring/breakout

27
Q

What method (x3) are used for testing inside ducts

A
  • Visual/endoscope (if poorly grouted)
  • Air pressure test (compressibility of air in voids)
  • X-ray

NB. testing inside ducts is done, as well as testing at anchorages

28
Q

Describe the different scopes (x3) of concrete repair works

A
  • Cosmetic
  • Structural
  • Strengthening
29
Q

Name four types of concrete repair works

A
  • ‘Concrete repair’
  • Crack injection
  • Surface protection systems
  • Bonded reinforcement (steel, carbon-fibre etc)
30
Q

What are two types of fibre strengthening application methods?

A
  • Fabric wrap
  • Pultruded plates
31
Q

Name two performance requirements of fibre strengthening?

A
  • Adhesive failure
  • Damage/deterioration