CIVE1173 repair techniques

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CIVE1173 repair techniques
2013-06-22 23:03:16
Service Life Modelling Repair Technique

Week 8 lecture notes summary. Exam
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  1. Lifecycle Modelling
  2. 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
  3. 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
  4. 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
  5. Incipient Anodes patch repair
  6. 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
  7. Cathodic Protection
    • Electrochemical protection
    • Impressed Current Cathodic Protection (ICCP) Sacrificial Anode; st5eel CP uses seawater as electrolyte
    • Hybrid CP
  8. Impressed Current Cathodic Protection (ICCP)
  9. Sacrificial Anode
    • Use a more reactive metal
  10. Hybrid CP
    • Initially impressed current. 
    • Once corrosion stops it then acts as a sacrificial anode.
    • No a currently industry standard system. Research underway.
  11. Cathodic Prevention
    • Identical to ICCP
    • Installed during construction
  12. 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
  13. Re-alkalisation
    • For carbonated concrete
    • Restores steel high pH; OH- generated at bar, OH- ingresses from surface
    • Temporary anode
    • Electrolyte media
  14. Silanes
    • Hydrophobic
    • No water = no chlorides
    • Oxygen reacts with Si in cement to bond to concrete
    • Spray, paint or as foam
    • Commerical coatings
  15. Inhibitors
    • Nitrate based; inhibit anodic reaction, must get concentration correct
    • Organic; amine based, monomolecular film, polar
  16. Crack Injection; small
    • Generally 0 to 0.3mm
    • Epoxy grout; no flowing water, good seal, no flexure
    • Polyurethane; flowing water, less durable, some flexure
  17. 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
  18. 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
  19. Concrete Cladding
    • Jacket the defect
    • May repair first
    • Apply; formwork & pumping, shotcrete
  20. Life Cycle Evaluation of Repairs/Maintenance
    • Damage (vertical), time (horiziontal)
    • Durability assessment defines damage curve & point on it. 
    • Horizontal baseline of serviceability required
  21. 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
  22. Life Cycle Costing
    • Relative repair cost (vertical), repair option (horizontal)
    • Can graph alternative life cycles next to each other