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DAMC > T4-x1: Repair Options and Problems with Patch Repairs > Flashcards

T4-x1: Repair Options and Problems with Patch Repairs Flashcards

(47 cards)

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1
Q

Give an overview of the basic repair options for reinforced concrete (x5)

A
  1. Do nothing
    - nothing needed
    - monitor
  2. Downgrade
    - limit loadings
    - load test
  3. Strengthen
  4. Preventative measures
    - surface protection
    - electrochemical methods
    - keep element dry
  5. Rebuild to new spec
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2
Q

[NAQ] whole-life strategy

A
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3
Q

What are the two components of GIS-based asset management systems?

A
  1. Routine inspections of key components
    - planned maintenance regime
  2. Life-cycle estimation of costs
    - permanent access systems
    - phasing of works
    - delayed intervention times
    - remote monitoring
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4
Q

What are three issues that can be found from a structural assessment

A
  1. Deterioration in structural performance
  2. Greater environmental loads
  3. Reworking to new codes and higher loads
    .
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5
Q

Give an overview of assessment techniques

A
  • Specialist analysis techniques (e.g. FE) may be used
  • Often assessing fatigue
  • Verification and calibration done using in-situ stress measurements and dynamic analysis
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6
Q

Name two things that assessment techniques might do

A
  • They might use specifically-developed departures from standards
  • They might allow for enhanced material properties
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7
Q

What does this image show, and why (x3)

A

A deteriorated condition
- reduced concrete area
- reduced reinforcement area
- reduced bond

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8
Q

What does this image show?

A

An idealised condition

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9
Q

Name four monitoring options (ie. different time scales)

A
  1. 24hr remote monitoring (real-time)
  2. 2-year general inspection
  3. 6-year principal inspection
  4. Targeted special inspection
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10
Q

What are three categories of probes used in concrete monitoring?

What are they detecting?

A
  1. Corrosion risk
    - half-cell
    - resistivity
    - corrosion rate
  2. Environment
    - temperature
    - RH (relative humidity)
    - precipitation
  3. Movement
    - structural
    - non-structural
    - event
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11
Q

What are five options for preventative maintenance and repair?

A
  1. Remove activators (chlorides, carbonation, water, sulfates etc)
  2. Replace weakened/cracked/delaminated material
  3. Clean and replace reinforcement
  4. Use (compatible) replacement materials
  5. Upgrade protection
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12
Q

For upgrading protection of concrete, what two things could be done?

Give two examples for each

A
  • Prevent ingress (coating, waterproofing)
  • Add extra cover (sprayed, recast)
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13
Q

What are two categories of upgraded/enhanced protection?

Electrochemical repair is one, what is the other

A
  1. Electrochemical repair
    - CP
    - ECE (electrochemical extraction)
    - ER (electrical resistance probes)
  2. Corrosion inhibitors
    - anodic
    - cathodic
    - mixed
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14
Q

Name four ‘activators’ for concrete degradation

A
  • Chlorides
  • Carbonation
  • Water
  • Sulfates
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15
Q

What are the aims (x2) of the patch repair process?

A
  • Remove carbonated concrete in contact with reinforcement
  • Remove all chloride above the corrosion threshold

ie. to remove all corrosion initiating contamination

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16
Q

[NAQ] overview of the patch repair process

A
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17
Q

For issues with patch repairs to do with carbonation, what are the factors (x8) that impact carbonation rate?

A
  • Temperature
  • Precipitation
  • External RH
  • Internal RH
  • Rural vs Urban
  • Cement content
  • W/C ratio
  • Curing
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18
Q

What is the relative humidity rate for

a) max. rate carbonation
b) max. rate corrosion
.

A

a) 50 - 70%
b) 80 - 95%

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19
Q

Summarise the carbonation process

Study These Flashcards
A
  • CO2 and H20 cause carbonation
  • Bars become active
  • Corrosion leads to cracking
20
Q

What can be done to treat carbonation (x2)?

Study These Flashcards
A
  • Apply an effective anti-carbonation coating to prevent non-active bar becoming active
  • Repair ‘perimeter’ to encompass all active and corroding bars
  • CO2 penetration reduced
21
Q

Name two sources of chloride ion contamination, at the mixing stage

Study These Flashcards
A
  • Admixtures (CaCl2 accelerator)
  • Aggregates from marine sources
22
Q

Name three sources of chloride ion contamination, at the in-service stage

Study These Flashcards
A
  • De-icing salt (e.g. bridges, car parks)
  • Maritime (e.g. in or within 5km of the sea)
  • Seawater-containing (e.g. swimming pools)
23
Q

[NAQ] half-cell mapping of a bridge

24
Q

For issues with patch repairs to do with chloride-contamination, what are the factors (x7) that impact chloride ion ingress?

Study These Flashcards
A
  • Temperature
  • Wetting/drying
  • CI concentration
  • Cement content
  • W/C ratio
  • Curing
  • Cement type
25
Summarise the chloride-ion ingress process Describe the threshold
- Chloride ions ingress, creating a 'chloride front' - **Bars become contaminated** with CI - In corrosion-free areas, cathodes form - Where **CI > 0.4%m** **corrosion sites (anodes) form** - This creates a '**corrosion current**' - Corrosion leads to cracking - Anodes increase in the corrosion current - Localised pitting on bar
26
Where is the half-cell reading going to be highest, for chloride-ion ingress?
In the middle, where **anodes increase in corrosion current** ie. at the anode sites
27
What can be done to treat chloride-ion ingress (x3)?
1. **Repair perimeter** to encompass all active and corroding bars with CI > 0.4% 2. **Coating** to prevent further chloride contamination 3. Have a **depth** sufficient to prevent back-diffusion
28
Where will the greatest half-cell potential readings be along a bar?
At the anode sites
29
What can happen in a failed patch repair (x2)?
- New delaminations - Spalling
30
Which image shows delamination, and which shows spalling?
Top = delamination Bottom = spalling
31
Name two features of cast-in chloride
- Constant CI-content - Risk increases with age
32
What increases the risk in cast-in chloride, and why?
**Carbonation** increases the risk - decomposes chloroaluminate complexes - **releases more free chloride ions**
33
[NAQ] risk-based case-in chloride
34
Name two categories (and subsequent types, x4) of repair systems?
1. **Electrochemical repair** - cathodic protection - **ECE** (electrochemical chloride extraction) - **Realkalisation** - **Electrochemical drying** (electro-osmosis) 2. **Corrosion inhibitors**
35
For structural upgrade, what (x3) can be improved/increased/ added to strengthen a structure?
1. **Structural bonding** - steel plate bonding - carbon, glass and aramid fibre 2. Increase **section size**/ reinforcement 3. Add **post-tensioning**
36
If replacing a structure, what can be done for max. effectiveness (x4)?
1. Have **improved spec** (to EC-2/ BS EN 206) 2. Have improved standards of working and site **quality control** 3. Have **lightweight, lift-in structures** - off-line fabrication, quickly installed 4. Have **easy inspection and maintenance provision**
37
What are five factors to consider in whole life factor modelling?
- Life to **first maintenance** - Life to **first failure** - Client requirements - Initial **costs** - Maintenance costs (e.g. access, labour)
38
What is a typical design life for: a) buildings b) roads and bridges
a) 60 years b) 120 years
39
What should a deterioration model consider (x3)?
1. The **deterioration processes** 2. Process retardation 3. **Options for repair**
40
Name four deterioration processes
- Carbonation - Chloride-ingress - Alkali-silica reaction - Erosion/attack
41
What will a piecemeal 'holding' repairs process have?
- Low cost when executed - High whole-life costs - Progressive weakening of structure
42
What will a (good) whole-life costed repair have?
- A plan that works in one large operation - Allows the structure to **deteriorate safely** (to design life) - **Miminised whole life expenditure** - **Minimised weakening** of structure
43
[NAQ] comparison of life-cycle costing for a 15-year and 60-year life
44
[NAQ] cost comparison of multiple vs. single repairs
NB. single is cheaper
45
What is another repair option, which requires no formwork?
Sprayed concrete
46
What is a solution to carbonation repair?
**Cut back** - **remove all active bar** and **precast** the concrete
47
What can occur if there is corrosion around a repair?
Incipient anode corrosion

DAMC (25 decks)

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