(2) repair of concrete_structures_case_studies
TRANSCRIPT
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REPAIR OF CONCRETE STRUCTURES
CASE STUDIES
DR SYED EHTESHAM HUSSAIN
CONCRETE TECHNOLOGY CONSULTANTS
(CONTEC)
KHOBAR
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CONCRETE DURABILITY PROBLEMS
IN THE GULF REGION
1. SEVERE EXPOSURE CONDITIONS
- High concentrations of chloride & sulfate ions in soil
- High salinity in seawater
- High temperature & temperature fluctuations
- High humidity
CONTEC - EVALUATION, STRUCTURAL ASSESSMENT, REHAB DESIGN, FAILURE ANALYSIS, NDT
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CONCRETE DURABILITY PROBLEMS
IN THE GULF REGION
2. POOR QUALITY MATERIALS
- Absorptive & dusty aggregates
- Contamination in sand and coarse aggregates
- Poorly graded sand
- High salinity in water
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CONCRETE DURABILITY PROBLEMS
IN THE GULF REGION
3. USE OF OLD (INAPPROPRIATE) SPECS.
- Type V cement or OPC (No mineral admixtures)
- High water-cement ratio
- Inadequate curing/curing period
- Low cover to reinforcement
- Poor workmanship
- Fast construction & lack of proper quality control
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PRESENT IMPROVED SPECIFICATIONS
- Type I cement (C3A > 8%)
- Mineral admixtures (silica fume, fly ash and slag)
- Low w/c ratio (< 0.40)
- High cover (75 mm)
- Additional protection
- QC techniques for durability
RESULTED IN IMPROVED SERVICE LIFE
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EFFECT OF EXPOSURE CONDITIONS
AND CONCRETE QUALITY ON LIFE
LIFE (YEARS)
CON
CO
NC
RE
TE
QU
AL
ITY
INC
RE
AS
ING
SE
VE
RITY
OF
EX
PO
SU
RE
10 20 30 40 50
NORMAL
ARABIAN GULF
NORMAL
70s-80s
PRESENT
ADDITIONAL PROTECTION
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COMMON REINFORCEMENT CORROSION PROBLEMS
1. Marine structures
2. Strcs. in contact with soil & groundwater
3. Strcs. exposed to excessive condensation
4. Bridge decks
5. Strcs. exposed to deposition of sand/dust
6. Deterioration due to design defects
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MARINE STRUCTURES
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STRCS. IN CONTACT WITH SOIL
& GROUNDWATER
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STRCS. EXPOSED TO EXCESSIVE CONDENSATION
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BRIDGE DECKS
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STRCS. EXPOSED TO DEPOSITION OF SAND/DUST
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DETERIORATION DUE TO
DESIGN DEFECTS
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PIPE OPENING IN WALL
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CABLE DUCT
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COMMON REPAIR TECHNIQUES
1. DO NOTHING
2. COATINGS
3. PATCH REPAIR
4. REPLACEMENT OF CHLORIDE CONTAMINATED CONCRETE
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COMMON REPAIR TECHNIQUES
5. RE-SKINNING – reconstruction of cover concrete
6. RE-CONSTRUCTION
7. CATHODIC PROTECTION
8. STRENGTHENING
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DO NOTHING
• STRUCTURE LEFT UNREPAIRED
• LOW LEVEL OF DETERIORATION
• LEVEL OF DETERIORATION IS STRUCTURALLY ACCEPTABLE
• REMAINING SERVICE LIFE IS LIMITED
• STRUCTURE CAN OPERATE UNDER REDUCED LOADS
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COATINGS
• BARRIER TO INGRESS OF CHLORIDES
• PROLONG SERVICE LIFE
• NO DETERIORATION
• CHLORIDE CONMTAMINATION LEVELS ARE LOW
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COATINGS
COMMONLY USED COATINGS
• ACRYLIC BASED CEMENTITIOUS COATINGS
• EPOXIES
• PULYURETHANE
• PENETRANTS (SILANES & SILOXANES)
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PATCH REPAIR
• UNSOUND CONCRETE REPLACED WITH REPAIR CONCRETE
• REPAIRED AND ADJACENT AREAS GENERALLY COATED
• CHLORIDE CONTAMINATED CONCRETE IS NOT REMOVED
• INCIPIENT ANODE CORROSION
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PATCH REPAIR
• GALVANIC ANODES IN UN-REPAIRED AREAS
• LOW INITIAL COST
• NEEDS TO BE REPEATED AT REGULAR INTERVALS
• LIFE CYCLE COST MAY BE HIGH
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RE-SKINNING
• ENTIRE COVER IS REPLACED WITH REPAIR CONCRETE
• COATED TO PROLONG LIFE
• CHLORIDE TESTING REQUIRED
• NO INCIPIENT ANODE CORROSION
• HIGH INITIAL COST
• LONG-TERM SOLUTION
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REPLACEMENT
• STRUCTURE OR ITS PART RECONSTRUCTED USING DURABLE CONCRETE
• EXTENSIVE DETERIORATION
• THIN SECTIONS – SLABS AND COLUMNS
• HIGH INITIAL COST
• LONG-TERM SOLUTION
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CATHODIC PROTECTION
• PATCH REPAIR OF UNSOUND CONCRETE
• DIRECT CURRENT PASSED BETWEEN INSTALLED ANODE AND REBARS
• CHLORIDES MOVE AWAY FROM THE REBARS
• ALKALINITY INCREASES AROUND REBARS
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CATHODIC PROTECTION
• CHLORIDE REMOVAL IS NOT REQUIRED
• LONG-TERM SOLUTION – LIFE OVER 40 YEARS
• NEEDS REGULAR MONITORING
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SELECTION OF REPAIR STRATEGY
FACTORS
• CAUSES OF DETERIORATION
• LEVEL OF DETERIORATION
• SEVERITY OF EXPOSURE CONDITIONS
• LEVEL OF CHLORIDE CONTAMINATION
• REQUIRED SERVICE LIFE
• FUTURE MAINTENANCE REQUIREMENTS
• INITIAL AND LIFE CYCLE COST
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SELECTION OF REPAIR TECHNIQUES
PRACTICAL EXAMPLES
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CASE 1 - LOW DEGREE OF DETERIORATION & LONG SERVICE LIFE
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CASE 1
• NO OR LOW DEGREE DETERIORATION
• MARINE EXPOSURE – HIGH RISK OF CHLORIDE CONTAMINATION
• LOW CHLORIDE CONTAMINATION IN CONCRETE
• REQUIRED SERVICE LIFE - LONG
APPROPRIATE REPAIR
COATING
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CASE 2 – LOCAL DETERIORATION
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CASE 2
• ISOLATED DETERIORATION
• LOCAL CAUSES (CONSTRUCTION DEFECTS, LEAKAGE etc.)
• MILD EXPOSURE CONDITIONS – LOW RISK OF CHLORIDE CONTAMINATION
• LOW CHLORIDE CONTAMINATION IN CONCRETE
APPROPRIATE REPAIR
PATCH REPAIR
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CASE 3 – EXTENSIVE DETERIORATION & LONG SERVICE LIFE
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CASE 3
• EXTENSIVE DETERIORATION
• SEVERE EXPOSURE CONDITIONS – HIGH RISK OF CHLORIDE CONTAMINATION
• HIGH CHLORIDE CONTAMINATION IN CONCRETE
• REQUIRED SERVICE LIFE - LONG
APPROPRIATE REPAIR
RE-SKINNING PLUS COATING
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CASE 4 – SEVERE EXPOSURE & LONG LIFE
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CASE 4
• LOW TO MODERATE DETERIORATION
• SEVERE EXPOSURE CONDITIONS – HIGH RISK OF CHLORIDE CONTAMINATION
• HIGH CHLORIDE CONTAMINATION IN CONCRETE
• REQUIRED SERVICE LIFE - LONG
APPROPRIATE REPAIR
CATHODIC PROTECTION
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CASE 5 – EXTENSIVE DETERIORATION& SHORT SERVICE LIFE
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CASE 5
• LOW TO MODERATE DETERIORATION
• SEVERE EXPOSURE CONDITIONS – HIGH RISK OF CHLORIDE CONTAMINATION
• HIGH CHLORIDE CONTAMINATION IN CONCRETE
• REQUIRED SERVICE LIFE - SHORT
APPROPRIATE REPAIR
PATCH REPAIR
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CASE 6 – SMALL SECTIONS
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CASE 6
• EXTENSIVE DETERIORATION
• THIN SECTIONS – SLABS, COLUMNS
• SEVERE EXPOSURE CONDITIONS – HIGH RISK OF CHLORIDE CONTAMINATION
• HIGH CHLORIDE CONTAMINATION IN CONCRETE
APPROPRIATE REPAIR
REPLACEMENT
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CONCLUDING REMARKS
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1. PREMATURE CONCRETE DETERIORATION
OBSERVED DUE TO
- AGGRESSIVE EXPOSURE CONDITIONS
- POOR QUALITY MATERIALS
- USE OF INAPPROPRIATE SPECIFICATIONS
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2. IMPROVEMENT IN SPECIFICATIONS IN
RECENT YEARS HAS IMPROVED THE SERVICE
LIFE OF STRUCTURES
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3. STRUCTURES SUSCEPTIBLE TO REINFORCEMENT CORROSION
INCLUDE
- Marine Strcs
- Strcs. In Contact With Soil/GW
- Strcs. Exposed To Condensation
- Strcs. With Accumulation of Dust
- Other Structures Exposed to Aggressive Conditions
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4. FACTORS TO BE CONSIDERED TO SELECT A
REPAIR STRATEGY
• Causes and Extent of Deterioration
• Severity of Exposure Conditions
• Level of Chloride Contamination
• Required Service Life
• Future Maintenance Requirements
• Initial and Life Cycle Cost
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5. PATCH REPAIR
• Provides Short Term Solution at Low Initial Cost
• Needs Repair at Regular Intervals
• Life Cycle Cost may be High
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6. RE-SKINNING
• Provides Long Term Solution
• High Initial Cost
• Suitable Where Deterioration is Extensive
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7. CATHODIC PROTECTION
• Provides Long Term Solution
• High Initial Cost
• Suitable Where Deterioration is Low, Chloride
Contamination is High and Exposure Conditions are
Severe