REPAIR OF CONCRETE STRUCTURES

CASE STUDIES

DR SYED EHTESHAM HUSSAIN

CONCRETE TECHNOLOGY CONSULTANTS

(CONTEC)

KHOBAR

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

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

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

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

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

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

MARINE STRUCTURES

STRCS. IN CONTACT WITH SOIL

& GROUNDWATER

STRCS. EXPOSED TO EXCESSIVE CONDENSATION

BRIDGE DECKS

STRCS. EXPOSED TO DEPOSITION OF SAND/DUST

DETERIORATION DUE TO

DESIGN DEFECTS

PIPE OPENING IN WALL

CABLE DUCT

COMMON REPAIR TECHNIQUES

1. DO NOTHING

2. COATINGS

3. PATCH REPAIR

4. REPLACEMENT OF CHLORIDE CONTAMINATED CONCRETE

COMMON REPAIR TECHNIQUES

5. RE-SKINNING – reconstruction of cover concrete

6. RE-CONSTRUCTION

7. CATHODIC PROTECTION

8. STRENGTHENING

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

COATINGS

• BARRIER TO INGRESS OF CHLORIDES

• PROLONG SERVICE LIFE

• NO DETERIORATION

• CHLORIDE CONMTAMINATION LEVELS ARE LOW

COATINGS

COMMONLY USED COATINGS

• ACRYLIC BASED CEMENTITIOUS COATINGS

• EPOXIES

• PULYURETHANE

• PENETRANTS (SILANES & SILOXANES)

PATCH REPAIR

• UNSOUND CONCRETE REPLACED WITH REPAIR CONCRETE

• REPAIRED AND ADJACENT AREAS GENERALLY COATED

• CHLORIDE CONTAMINATED CONCRETE IS NOT REMOVED

• INCIPIENT ANODE CORROSION

PATCH REPAIR

• GALVANIC ANODES IN UN-REPAIRED AREAS

• LOW INITIAL COST

• NEEDS TO BE REPEATED AT REGULAR INTERVALS

• LIFE CYCLE COST MAY BE HIGH

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

REPLACEMENT

• STRUCTURE OR ITS PART RECONSTRUCTED USING DURABLE CONCRETE

• EXTENSIVE DETERIORATION

• THIN SECTIONS – SLABS AND COLUMNS

• HIGH INITIAL COST

• LONG-TERM SOLUTION

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

CATHODIC PROTECTION

• CHLORIDE REMOVAL IS NOT REQUIRED

• LONG-TERM SOLUTION – LIFE OVER 40 YEARS

• NEEDS REGULAR MONITORING

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

SELECTION OF REPAIR TECHNIQUES

PRACTICAL EXAMPLES

CASE 1 - LOW DEGREE OF DETERIORATION & LONG SERVICE LIFE

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

CASE 2 – LOCAL DETERIORATION

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

CASE 3 – EXTENSIVE DETERIORATION & LONG SERVICE LIFE

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

CASE 4 – SEVERE EXPOSURE & LONG LIFE

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

CASE 5 – EXTENSIVE DETERIORATION& SHORT SERVICE LIFE

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

CASE 6 – SMALL SECTIONS

CASE 6

• EXTENSIVE DETERIORATION

• THIN SECTIONS – SLABS, COLUMNS

• SEVERE EXPOSURE CONDITIONS – HIGH RISK OF CHLORIDE CONTAMINATION

• HIGH CHLORIDE CONTAMINATION IN CONCRETE

APPROPRIATE REPAIR

REPLACEMENT

CONCLUDING REMARKS

1. PREMATURE CONCRETE DETERIORATION

OBSERVED DUE TO

- AGGRESSIVE EXPOSURE CONDITIONS

- POOR QUALITY MATERIALS

- USE OF INAPPROPRIATE SPECIFICATIONS

2. IMPROVEMENT IN SPECIFICATIONS IN

RECENT YEARS HAS IMPROVED THE SERVICE

LIFE OF STRUCTURES

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

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

5. PATCH REPAIR

• Provides Short Term Solution at Low Initial Cost

• Needs Repair at Regular Intervals

• Life Cycle Cost may be High

6. RE-SKINNING

• Provides Long Term Solution

• High Initial Cost

• Suitable Where Deterioration is Extensive

7. CATHODIC PROTECTION

• Provides Long Term Solution

• High Initial Cost

• Suitable Where Deterioration is Low, Chloride

Contamination is High and Exposure Conditions are

Severe