State-of-the-Art-Report: Corrosion and Corrosion Protection of Prestressed Concrete Bridges in Marine Environment

IRC SOR 18: Introduction - Key Formulas, Tables & Specifications

1. Pulse Velocity & Compressive Strength

• Compressive Strength (If) estimation from Pulse Velocity (V):

[ If = 4.776 \times V^{0.55} \quad \text{(V in km/s)} ]

• Pulse velocity (V) relates to Elastic Modulus (E) and Density (D):

[ V = K \sqrt{\frac{E}{D}} ]

where,
K = constant,
E = Modulus of Elasticity,
D = Density of concrete.

2. Minimum Pulse Velocity for Acceptance (Table 4.4)

3. Steel Influence Zone in UPV Measurements

[ \frac{a}{l} < \frac{1}{2} ]

• a = perpendicular distance from steel centerline to transducer edge
• l = shortest distance between transducers

If within steel influence, apply correction factor K to measured velocity.

4. Applications & Observations

• UPV technique detects concrete quality variations, cracks, and deterioration.
• 10% decrease in pulse velocity ≈ 20% decrease in dynamic modulus.
• Recommended to avoid steel influence in pulse path for accuracy.

flowchart LR
    A[Pulse Velocity Measurement] --> B{Steel Influence?}
    B -- No --> C[Use Measured Velocity]
    B -- Yes --> D[Apply Correction Factor K]
    C --> E[Estimate Compressive Strength & Elastic Modulus]
    D --> E

Summary: IRC SOR 18 introduces pulse velocity as a non-destructive method to assess concrete quality, strength, and damage, with key empirical formulas and acceptance criteria for prestressed and reinforced concrete structures.

IRC SOR 18: Case Studies of Corrosion Failures – Key Points

Though the code does not provide explicit formulas or tables under "Case Studies of Corrosion Failures," related sections and typical practices include:

Key Concepts & Specifications

• Stress Corrosion Cracking (SCC):
  Model stages (Clause 3.2) show prestressing steel degradation in ammonium nitrate environments.

• Electrochemical Monitoring:
  Use of reference electrodes for corrosion potential measurement:

  • Saturated Calomel Electrode (SCE)
  • Silver/Silver Chloride Electrode
  • Copper/Copper Sulphate Electrode

• Corrosion Measurement Techniques:

  • Open Circuit Potential (OCP)
  • Surface Potential Mapping
  • Guard-Ring Technique for localized corrosion
  • Impedance Spectroscopy (Nyquist plots for corrosion rate)

Typical Corrosion Rate Estimation Formula

[ i_{corr} = \frac{B}{R_p} ] Where:

• (i_{corr}) = corrosion current density (μA/cm²)
• (B) = Stern-Geary constant (typically 26 mV for steel)
• (R_p) = polarization resistance (Ω·cm²)

Common Corrosion Forms

• Uniform corrosion
• Pitting corrosion
• SCC
• Galvanic corrosion

Summary Table Example (from related sections)

flowchart LR
    A[Exposure to Corrosive Medium] --> B[Initiation of Corrosion]
    B --> C[Propagation: SCC or Pitting]
    C --> D[Crack Growth or Pit Expansion]
    D --> E[Structural Failure]

Recommendation: Use electrochemical methods (OCP, impedance) to monitor corrosion in prestressed concrete; analyze case studies for environmental and material factors influencing failure modes.

Forms of Corrosion (IRC SOR 18 context + general knowledge):

• Uniform Corrosion: Even metal loss over surface.
• Pitting Corrosion: Localized small pits, highly damaging.
• Crevice Corrosion: Occurs in shielded areas (joints, under deposits).
• Stress Corrosion Cracking (SCC): Cracks due to tensile stress + corrosive environment.
• Galvanic Corrosion: Between dissimilar metals in contact.
• Intergranular Corrosion: Along grain boundaries.
• Erosion Corrosion: Accelerated by fluid motion.

Factors Influencing Corrosion:

Key Formula: Corrosion Rate (mm/year)

[ \text{Corrosion Rate} = \frac{K \times W}{\rho \times A \times T} ]

Where:

• (K = 8.76 \times 10^4) (constant for mm/year)
• (W =) Weight loss (mg)
• (\rho =) Density (g/cm³)
• (A =) Area (cm²)
• (T =) Time (hours)

Diagram: Stress Corrosion Cracking Process (Clause 3.2)

flowchart LR
    A[Applied Tensile Stress] --> B[Micro-crack Initiation]
    B --> C[Crack Propagation]
    C --> D[Sudden Fracture]
    E[Corrosive Environment] --> B
    E --> C

For detailed monitoring and protective methods, see clauses 4.x and sections on electrodes and instrumentation.

Monitoring Aspects per IRC SOR 18 (Clause 6.3 & related)

Key Monitoring Parameters for Prestressed Concrete:

• Corrosion Monitoring:

  • Non-prestressing and Prestressing Steel:
    • Open Circuit Potential (OCP): ASTM C 876-80 standard; potential ranges indicate corrosion probability but not corrosion rate.
    • Surface Potential Measurements: Identify vulnerable regions; must be combined with resistivity.
    • Concrete Resistivity: Quality control; monitors concrete deterioration; no direct corrosion rate correlation.
    • Corrosion Cell Ratio: Ratio from surface potential & resistivity; indicates corrosion probability.
    • Electrical Resistance Probe: Measures cross-sectional loss; sensitive to uniform corrosion, not pitting.
    • Polarisation Resistance Technique: Electrochemical corrosion rate; field application challenges.
    • Impedance Technique: Emerging AC impedance spectroscopy for in-situ corrosion quantification.

• Crack Width and Corrosion:

  • Cracks ≤ 0.1 mm: No corrosion observed.
  • Cracks 0.1 to 2.5 mm: Severe corrosion likely.

• Chloride Thresholds:

  • Max chloride in cement: 0.06% by weight.
  • Threshold varies with water-cement ratio (e.g., 0.4 w/c → 0.26%, 0.28 w/c → 0.17% chloride).
  • Pitting may start at ~3200 ppm chloride in pore solution.

• Concrete Cover Quality:

  • Permeability coefficient max: 10⁻¹² m/s (DNV standard).
  • Cover thickness measured by covermeter/profometer (max cover measurable ~120 mm).

• Crack Depth Measurement:

  • By coring or NDT methods like Ultrasonic Pulse Velocity.

Summary Table: Corrosion Monitoring Techniques

Protective Aspects per IRC SOR 18

1. Protective Barrier System Categories (Table 5.1)

2. Protective Coatings Highlights

• Neoprene (Clause 1.75): Two-part coatings, thickness 0.25–1.75 cm; excellent water, chemical, oil resistance; acid resistant.
• Polysulfide: Excellent ozone, sunlight, oxidation resistance; poor heat/abrasion resistance.
• Coal tar epoxy: Tough, good chemical and abrasion resistance; suitable for immersion.
• Polysulfide-epoxy: Combines flexibility and adhesion; good chemical resistance.

3. Concrete Sealers (Clause 5.4.4)

• Sealers reduce water ingress by filling pores or lining with water repellents.
• Types: silicone resins, acrylics, epoxies, polyurethanes, alkaline silicates.
• Used mainly for corrosion protection of embedded steel, especially in bridge decks.
• Typical thickness: varies; often combined with surface layers like 12 mm roastic asphalt.

Summary

• Select protective systems based on chemical severity, thickness, and exposure type.
• Use sealers for waterproofing to prevent steel corrosion.
• Refer Table 5

The IRC SOR 18 code does not provide explicit formulas or tables under the "Summary and Conclusion" section. However, based on the overall context of corrosion in prestressing steel and concrete, here are key points and typical specifications relevant to corrosion monitoring and protection:

Key Concepts from IRC SOR 18

• Stress Corrosion Cracking (SCC) stages are modeled to understand prestressing steel deterioration.
• Use of reference electrodes (Saturated Calomel, Silver/Silver Chloride, Copper/Copper Sulphate) for potential measurements.
• Open Circuit Potential (OCP) and surface potential methods for corrosion detection.
• Electrical circuits and instrumentation like FPR Meter, AC Corrosion Monitor, and Impedance Instrumentation are used for on-site corrosion monitoring.
• Equivalent circuits and Nyquist plots help interpret corrosion behavior.

Typical Corrosion Monitoring Parameters

Summary Recommendations

• Regular potential measurements using standard electrodes.
• Use of electrochemical impedance spectroscopy for detailed corrosion assessment.
• Protective measures include coatings, cathodic protection, and corrosion inhibitors.
• Continuous monitoring critical in aggressive environments (e.g., ammonium nitrate medium).

flowchart LR
    A[Prestressing Steel] --> B[Exposure to Aggressive Medium]
    B --> C[Stress Corrosion Cracking]
    C --> D[Corrosion Monitoring]
    D --> E[Electrode Measurements]
    D --> F[Electrochemical Impedance]
    E --> G[OCP & Surface Potential]
    F --> H[Nyquist Plot & Rp]
    D --> I[Protective Measures]
    I --> J[Coatings]
    I --> K[Cathodic Protection]
    I --> L[Inhibitors]

This summary aligns with the detailed monitoring and protective strategies outlined in the IRC S

Scope for Further Research in IRC SOR 18 focuses on advanced R&D proposals targeting corrosion and protection of prestressed concrete bridges in marine environments. Key elements include:

R&D Proposals Overview (Clause 7.1)

Key Specifications and Tools

• Instrumentation: Electrical resistance probes, vibrating wire strain gauges, FFT analyzers.
• Corrosion Monitoring: Impedance spectroscopy, open circuit potential measurements.
• Protective Systems: Chemical inhibitors, powder epoxy coatings, VPI wrappers.
• Repair Materials: Epoxies, polymers standardized for PSC and RCC.
• Data Analysis: Correlation of field measurements with design data for residual life estimation.

Time Management

• Tasks are organized via PERT charts (Figs. 7.1 to 7.4) detailing procurement, installation, measurement, analysis, and reporting phases.

gantt
    title R&D Proposal 1 Timeline
    dateFormat  MM
    section Task 1: Equipment Procurement & Fixing
    Procurement          :done, 1, 6
    Fixing Probes        :done, 7, 6
    Measurements         :active, 13, 6
    Analysis             : 19, 12
    Report               : 31, 6

This structured R&D approach ensures systematic development of corrosion monitoring, protection, and repair techniques aligned with marine bridge durability challenges.

IRC SOR 18 - R&D Proposal No. 1: Instrumentation for Monitoring Corrosion

Key Specifications & Tasks

• Objective: Monitor corrosion of prestressing steel/reinforcement in PSC and RCC bridges.
• Instrumentation includes:
  • Electrical resistance probes for corrosion rate.
  • Gamma radiography for internal inspection.
  • Deflection & slope measurements (precision level, Gilt meter).
  • Strain gauges (mechanical/vibrating wire).
  • Vibration frequency measurement with FFT analyzer.
  • Concrete specimen testing.

Action Plan (Summary)

Electrochemical Corrosion Monitoring (Key Formula)

• Equivalent Circuit:

  • ( R ) = concrete resistance
  • ( C_a ) = double layer capacitance
  • ( R_t ) = charge transfer resistance

• Impedance:
  [ |Z| = R + \frac{1}{j\omega C_a} + R_t ] where ( \omega = 2\pi f ), ( j = \sqrt{-1} )

• Corrosion current (Stern-Geary Equation):
  [ i_{corr} = \frac{B}{R_t} ] where ( B ) is a constant depending on anodic and cathodic Tafel slopes.

Notes:

• AC impedance spectroscopy is effective for measuring low corrosion rates and distinguishing corrosion mechanisms.
• Electrical resistance probes give direct corrosion rate by measuring metal loss.
• Gamma radiography helps detect internal defects without damaging the structure.

flowchart TD
    A[Procurement of Equipment] --> B[Installation of Probes]
    B --> C[Corrosion Measurements]
    C --> D[Data Analysis]
    D --> E[Report Preparation]

References: Stern & Ge

Key Details from IRC SOR 18 on R&D Proposal No. 2: Corrosion Protection Systems for Prestressing Steel

Objectives & Tasks:

• Identify cost-effective corrosion protection for prestressing steel.
• Tasks include:
  • Procurement of chemicals and equipment
  • Fabrication of anchorage bed
  • Study of passivating systems for steel in cable ducts
  • Evaluation of inhibitor admixtures during grouting
  • Protective lacquer coatings at manufacturer’s end
  • VPI (Vacuum Pressure Impregnation) wrappers for storage/transit
  • Powder epoxy coating studies on prestressing steel

Time Frame Summary (Months):

Important Specifications & Findings:

• Prestressing Steel Characteristics:

  • Cold-drawn, stress-relieved eutectoid steel, diameter 1.5-8 mm.
  • Highly sensitive to corrosion due to high strength and cold-drawn surface.
  • Vulnerable to pitting, stress corrosion cracking, hydrogen embrittlement.

• Corrosion Protection Methods:

  • Inhibitor admixtures in grout neutralize chloride effects.
  • Inhibited cement slurry coating increases durability by 25-35 times even in cracked concrete.
  • Powder epoxy coatings provide barrier protection but may cause galvanic corrosion if defective.
  • Passivating cement slurry preferred over powder epoxy for chemical resistance and reduced galvanic corrosion.
  • VPI wrapping protects during storage

R&D Proposal No. 3: Repair and Rehabilitation Methods (IRC SOR 18)

This proposal aims to evolve and standardize cost-effective repair and rehabilitation methods for PSC and RC structures.

Key Tasks & Timeline (months)

Important Specifications & Notes:

• Materials: Epoxies, polymers, and other repair materials must be procured and tested for compatibility and durability.
• Standardization: Steps for repair must be standardized separately for PSC and RC structures considering their specific behaviors.
• Model Specimens: Design and casting of models are essential for evaluating repair methods under controlled conditions.
• Evaluation: Both concrete and steel repair systems are evaluated for effectiveness.
• Data Analysis: Critical to refine repair methods based on test results.
• Report: Final documentation for dissemination and implementation.

Additional Useful Information from IS Context:

• Electrical Resistivity Testing: Used to assess concrete quality and porosity, which influences repair strategy.
• Coating Evaluation: Surface

R&D Proposal No. 4: Corrosion Rate Quantification & Residual Life Estimation (IRC SOR 18)

Key Tasks & Specifications:

• Task 1: Collect design data; identify worst loading/location.
• Task 2-4: Prototype model design; study deflection, vibration, strain; include accelerated electrochemical corrosion to assess load capacity changes.
• Task 5: Corrosion survey on actual bridge using impedance spectroscopy or equivalent for corrosion quantification.
• Task 6: Monitor deflection/vibration/strain on actual bridge; correlate with design data.
• Task 7: Correlate tasks 5 & 6 for validation.

Important Formulas & Concepts:

1. Corrosion Rate (CR) from Electrical Resistance Probe:

[ CR = \frac{K \times \Delta R}{A \times t} ]

• (K) = constant depending on probe material
• (\Delta R) = change in resistance
• (A) = cross-sectional area
• (t) = time

2. Residual Life Estimation:

[ \text{Residual Life} = \frac{\text{Allowable Loss of Steel Thickness}}{\text{Corrosion Rate}} ]

Monitoring Techniques:

• Impedance Spectroscopy: Measures electrochemical impedance to quantify corrosion damage.
• Strain & Vibration Sensors: Mechanical/vibrating wire strain gauges, FFT analyzers for structural behavior.
• Electrochemical Methods: Open circuit potential, Nyquist plots for corrosion kinetics.

Time Frame Overview (Months):

flowchart TD
    A[Collect Design Data] --> B[Prototype Model Design]
    B --> C[Accelerated Electrochemical Corrosion]
    C --> D[Corrosion Survey on Actual Bridge]
    D --> E[Monitor Deflection/Vibration/Strain]
    E --> F[Correlation & Residual Life Estimation]

References: