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Repair technique
- Do Nothing: Structure has no defects, Maintain current inspection regime
- Regular Inspection: Structure has minor defects, Set periods for future inspection and low level maintenance if required
- Repair/Maintenance: Structure poses no immediate threat but requires action, Propose repair/maintenance options together with costs and time frames
- Immediate Action: Structure poses an immediate concern to safety, Close structure or impose restrictions (such as maximum load), Prepare repair options and costs for immediate action
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Repair options
- Patch Repair; 5-10 years, low cost
- Cathodic Protection Embedded; 20-30 years, medium-high cost
- Cathodic Protection Sacrificial; 10-15 years, medium cost
- Cathodic Prevention; 20-40 years, medium cost
- Desalination; 10-15 years, medium cost
- Silane coating; 15-20 years, low to medium cost
- Patch +Silanes, 15-25 years, medium-high cost
- see pp 4-6 of Week 9 lecture notes
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Patch repair concrete
- Identify area; Delamination survey, Potential Map, Chloride Profiles
- Breakout concrete; Hydroblasting, Mechanical removal
- Prepare surface; remove all contaminated, square edges
- Select repair material/appropriate product. e.g. cementious or paint
- Apply & cure
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Incipient Anodes patch repair
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Patch repair steel
- A Steel patch applied to corroded steel section Welded over corroded area
- Can be small section or whole circumference of pile
- Wrapping usually applied following application
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Cathodic Protection
- Electrochemical protection
- Impressed Current Cathodic Protection (ICCP) Sacrificial Anode; st5eel CP uses seawater as electrolyte
- Hybrid CP
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Impressed Current Cathodic Protection (ICCP)
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Sacrificial Anode
- Use a more reactive metal
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Hybrid CP
- Initially impressed current.
- Once corrosion stops it then acts as a sacrificial anode.
- No a currently industry standard system. Research underway.
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Cathodic Prevention
- Identical to ICCP
- Installed during construction
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Desalination
- aka Electrochemical Chloride Extraction
- Temporary anode to surface
- Chloride ions repulsed by steel (cathode) and drawn out of concrete to anode
- Pulsed on and off
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Re-alkalisation
- For carbonated concrete
- Restores steel high pH; OH- generated at bar, OH- ingresses from surface
- Temporary anode
- Electrolyte media
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Silanes
- Hydrophobic
- No water = no chlorides
- Oxygen reacts with Si in cement to bond to concrete
- Spray, paint or as foam
- Commerical coatings
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Inhibitors
- Nitrate based; inhibit anodic reaction, must get concentration correct
- Organic; amine based, monomolecular film, polar
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Crack Injection; small
- Generally 0 to 0.3mm
- Epoxy grout; no flowing water, good seal, no flexure
- Polyurethane; flowing water, less durable, some flexure
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Crack Injection; large
- Generally 0.5 to 5mm
- As crack size increases move from epoxy to cementious
- Patch repair may be better
- Epoxy grouts, Polyurethanes, Polymer modified cements, Flowing cements
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Fibre Reinforced Plastic (FRP)
- Structural strengthening
- Composite material
- Polymer; Epoxy, Polyester, Vinylester
- Fibre; glass, carbon
- For columns, beams or decks
- Glued to surface, recently used on Westgate Bridge
- Issues; Anchoring, Unravel at end, UV degradation, Glue
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Concrete Cladding
- Jacket the defect
- May repair first
- Apply; formwork & pumping, shotcrete
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Life Cycle Evaluation of Repairs/Maintenance
- Damage (vertical), time (horiziontal)
- Durability assessment defines damage curve & point on it.
- Horizontal baseline of serviceability required
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Asset Management Strategies
- Graph one-hit repairs or multiple repairs
- Deterioration (vertical, negative), time (horiziontal)
- Horizontal baselines of cracking, severe loss of section, failure
- Vertical baseline of Design Life
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Life Cycle Costing
- Relative repair cost (vertical), repair option (horizontal)
- Can graph alternative life cycles next to each other
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