State-of-the-Art-Report: Corrosion and Corrosion Protection of Prestressed Concrete Bridges in Marine Environment
1996 Edition

IRC SOR 18: Overview and Essential Formulas

1. Pulse Velocity and Estimation of Compressive Strength

• Relationship between compressive strength (If) and pulse velocity (V in km/s):

[ If = 4.776 \times V^{0.55} ]

• Pulse velocity connected to elastic modulus (E) and concrete density (D):

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

where K is a constant.

2. Minimum Acceptable Pulse Velocity Values

3. Steel Influence in Ultrasonic Pulse Velocity (UPV) Testing

Steel influence factor defined as:

[ \frac{a}{l} < 0.5 ]

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

Corrections applied if steel influence is detected.

4. Applications and Observations

• UPV helps detect concrete quality variations and cracks.
• A 10% drop in pulse velocity indicates approximately 20% reduction in dynamic modulus.
• Avoiding steel influence improves measurement accuracy.

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

Summary: The report introduces pulse velocity as a non-destructive evaluation method to assess concrete integrity, strength, and damage in prestressed and reinforced concrete structures.

IRC SOR 18: Examination of Corrosion Failures

Though explicit formulas are not presented under this section, the report discusses:

Key Concepts

• Stress Corrosion Cracking (SCC): Modeling steel degradation in ammonium nitrate environments.
• Electrochemical Monitoring: Use of reference electrodes such as Saturated Calomel, Silver/Silver Chloride, and Copper/Copper Sulphate for corrosion potential measurement.
• Corrosion Measurement Methods: Open Circuit Potential (OCP), surface potential mapping, guard-ring technique, and impedance spectroscopy (Nyquist plots).

Corrosion Rate Estimation

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

• (i_{corr}) is corrosion current density,
• (B) is Stern-Geary constant (~26 mV for steel),
• (R_p) is polarization resistance.

Common Corrosion Types

• Uniform corrosion
• Pitting
• Stress corrosion cracking
• Galvanic corrosion

Summary Table

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

Recommendation: Employ electrochemical techniques such as OCP and impedance spectroscopy for monitoring corrosion in prestressed concrete and study case histories to understand environmental and material influences.

Classification of Corrosion Forms

• Uniform Corrosion: Even metal loss over the surface.
• Pitting Corrosion: Localized, small but deep pits causing stress concentration.
• Crevice Corrosion: Occurs in shielded areas like joints or deposits.
• Stress Corrosion Cracking (SCC): Cracking caused by tensile stress combined with corrosive environment.
• Galvanic Corrosion: Between different metals in electrical contact.
• Intergranular Corrosion: Along grain boundaries.
• Erosion Corrosion: Accelerated by fluid flow.

Factors Affecting Corrosion:

Corrosion Rate Formula (mm/year)

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

Where:

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

Stress Corrosion Cracking Process

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

Refer to sections on electrodes and instrumentation for monitoring and protection methods.

Monitoring Protocols (IRC SOR 18 Clause 6.3 and related)

Key Parameters for Monitoring:

• Corrosion Detection:

  • Prestressing and Non-prestressing Steel:
    • Open Circuit Potential (OCP): As per ASTM C 876-80; indicates likelihood of corrosion but not rate.
    • Surface Potential Mapping: Locates susceptible zones; combined with resistivity for accuracy.
    • Concrete Resistivity: Indicates concrete quality and deterioration; not directly correlated to corrosion rate.
    • Corrosion Cell Ratio: Derived from surface potential and resistivity to assess corrosion risk.
    • Electrical Resistance Sensors: Measure cross-sectional loss; sensitive primarily to uniform corrosion.
    • Polarization Resistance Method: Electrochemical approach for corrosion rate; challenging for field use.
    • Impedance Spectroscopy: Emerging AC technique for in-situ corrosion quantification.

• Crack Impact:

  • Cracks ≤ 0.1 mm show no corrosion.
  • Cracks from 0.1 to 2.5 mm indicate high corrosion susceptibility.

• Chloride Limits:

  • Maximum 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%).
  • Pitting initiates around 3200 ppm chloride in pore solution.

• Concrete Cover:

  • Max permeability coefficient: 10⁻¹² m/s (DNV standard).
  • Cover thickness measured via covermeter or profometer (max ~120 mm).

• Crack Depth Measurement:

  • Via coring or non-destructive methods like Ultrasonic Pulse Velocity.

Summary Table of Monitoring Methods

For detailed monitoring techniques, see clauses 6.x and instrumentation sections.

Protection Strategies as per IRC SOR 18

1. Protective Barrier System Types (Reference Table 5.1)

2. Noteworthy Protective Coatings

• Neoprene: Two-component coatings, thickness 0.25–1.75 cm; excellent resistance to water, chemicals, oils, and acids.
• Polysulfide: Outstanding ozone, sunlight, and oxidation resistance; poor against heat and abrasion.
• Coal Tar Epoxy: Durable with good chemical and abrasion resistance; suitable for immersion.
• Polysulfide-Epoxy: Combines flexibility and adhesion with chemical resistance.

3. Concrete Sealers (Clause 5.4.4)

• Sealers reduce water penetration by filling pores or applying water-repellent liners.
• Types include silicone resins, acrylics, epoxies, polyurethanes, and alkaline silicates.
• Mainly used to protect embedded steel, especially in bridge decks.
• Often combined with surface layers such as 12 mm thick roastic asphalt.

Summary

• Protective systems should be selected based on chemical exposure severity, required thickness, and environmental conditions.
• Sealers are critical for waterproofing to prevent steel corrosion.
• Refer to Table 5.1 for detailed system selection guidance.

While IRC SOR 18 does not present direct formulas or tables in the concluding section, the overall document emphasizes:

Essential Insights

• Modeling of stress corrosion cracking stages to understand prestressing steel degradation.
• Use of reference electrodes (Saturated Calomel, Silver/Silver Chloride, Copper/Copper Sulphate) for corrosion potential measurement.
• Corrosion detection via Open Circuit Potential (OCP) and surface potential techniques.
• Application of electrical instrumentation such as FPR Meters, AC Corrosion Monitors, and impedance devices for field corrosion monitoring.
• Interpretation tools including equivalent circuits and Nyquist plots.

Typical Monitoring Parameters

Recommendations

• Routine potential measurements with standard electrodes.
• Employ electrochemical impedance spectroscopy for detailed corrosion analysis.
• Protective measures include coatings, cathodic protection, and corrosion inhibitors.
• Continuous monitoring is vital in aggressive environments such as ammonium nitrate exposure.

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 Spectroscopy]
    E --> G[OCP & Surface Potential]
    F --> H[Nyquist Plots & Rp]
    D --> I[Protection Strategies]
    I --> J[Coatings]
    I --> K[Cathodic Protection]
    I --> L[Inhibitors]

This synthesis aligns with the comprehensive corrosion monitoring and protection methods detailed in IRC SOR 18.

Prospects for Advanced Research as per IRC SOR 18

Research & Development Proposals (Clause 7.1)

Key Equipment and Methods

• Electrical resistance probes, vibrating wire strain gauges, FFT analyzers.
• Corrosion monitoring via impedance spectroscopy and open circuit potential measurements.
• Protective systems including chemical inhibitors, powder epoxy coatings, and vacuum pressure impregnation (VPI) wraps.
• Repair materials standardized for PSC and RCC.
• Data analysis correlating field measurements with design for residual life estimation.

Scheduling

• Tasks organized using PERT charts showing procurement, installation, measurement, analysis, and reporting phases.

gantt
title R&D Proposal 1 Timeline
dateFormat MM
section Equipment Procurement & Installation
Procurement          :done, 1, 6
Installation         :done, 7, 6
Monitoring           :active, 13, 6
Analysis             : 19, 12
Reporting            : 31, 6

This structured research approach facilitates systematic improvements in corrosion monitoring, protection, and repair technologies tailored for marine bridge durability.

IRC SOR 18 - R&D Proposal 1: Corrosion Monitoring Instrumentation

Key Specifications & Tasks

• Objective: Monitor corrosion behavior of prestressing steel and reinforcement in PSC and RCC bridges.
• Instruments include:
  • Electrical resistance probes for corrosion rate measurement.
  • Gamma radiography for internal condition assessment.
  • Deflection and slope measurements using precision levels and gilt meters.
  • Strain gauges (mechanical and vibrating wire types).
  • Vibration frequency monitoring via FFT analyzers.
  • Concrete specimen testing.

Action Plan Summary

Electrochemical Monitoring Formulae

• Equivalent circuit elements:

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

• Impedance expression:

[ |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} ]

with (B) being a constant based on the anodic and cathodic Tafel slopes.

Notes:

• AC impedance spectroscopy is effective for detecting low corrosion rates and differentiating corrosion mechanisms.
• Electrical resistance probes provide direct corrosion rate by metal loss measurement.
• Gamma radiography enables internal defect detection without structural damage.

flowchart TD
    A[Procure Equipment] --> B[Install Probes]
    B --> C[Conduct Corrosion Measurements]
    C --> D[Perform Data Analysis]
    D --> E[Prepare Reports]

References: Stern & Geary

IRC SOR 18 - R&D Proposal 2: Corrosion Protection for Prestressing Steel

Objectives and Activities:

• Develop economical corrosion protection methods for prestressing steel.
• Activities:
  • Procurement of chemicals and equipment.
  • Fabrication of anchorage beds.
  • Evaluation of passivation systems for steel in cable ducts.
  • Assessment of inhibitor admixtures in grouting materials.
  • Protective lacquer coatings at manufacturing stage.
  • Vacuum Pressure Impregnation (VPI) wrapping for storage and transit protection.
  • Studies on powder epoxy coatings of prestressing steel.

Timeline Summary (Months)

Important Details:

• Prestressing steel is cold-drawn, stress-relieved eutectoid steel of 1.5-8 mm diameter.
• Highly vulnerable to corrosion due to high strength and cold work.
• Susceptible to pitting, stress corrosion cracking, and hydrogen embrittlement.
• Protection methods:
  • Inhibitor admixtures neutralize chloride effects in grout.
  • Inhibited cement slurries increase durability by 25-35 times, even in cracked concrete.
  • Powder epoxy coatings provide barrier protection but may cause galvanic corrosion if compromised.
  • Passivating cement slurries are preferred for chemical resistance and reduced galvanic effects.
  • VPI wrapping safeguards during storage and transportation.

R&D Proposal 3: Development and Standardization of Repair and Rehabilitation Methods

Primary Goals

• Establish cost-effective, standardized repair methods for prestressed and reinforced concrete structures.

Work Plan and Schedule

Key Points

• Repair materials must be compatible and durable.
• Separate standardization for PSC and RC structures due to their differing properties.
• Model specimens essential for controlled evaluation.
• Both concrete and steel repair techniques assessed.
• Data analysis critical to refine methods.

Additional Notes

• Electrical resistivity testing helps assess concrete porosity impacting repair choices.
• Surface coating evaluation ensures durability and adhesion.

R&D Proposal 4: Quantifying Corrosion Rate and Estimating Remaining Service Life

Main Tasks

• Collect design and loading data; identify critical sections.
• Design prototype models; evaluate deflection, vibration, and strain.
• Conduct accelerated electrochemical corrosion tests to assess structural capacity reduction.
• Perform corrosion surveys on in-service bridges using impedance spectroscopy.
• Monitor deflection, vibration, and strain on actual structures; correlate with design data.
• Validate findings by correlating laboratory and field data.

Important Equations

1. Corrosion rate from electrical resistance probes:

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

• (K): probe-specific constant
• (\Delta R): change in electrical resistance
• (A): probe cross-sectional area
• (t): time interval

2. Residual life estimation:

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

Monitoring Techniques

• Impedance spectroscopy for corrosion quantification.
• Strain and vibration sensors including vibrating wire gauges and FFT analyzers.
• Electrochemical methods such as open circuit potential and Nyquist plot analysis.

Timeline

flowchart TD
    A[Collect Design Data] --> B[Design Prototype Models]
    B --> C[Accelerated Corrosion Testing]
    C --> D[Corrosion Survey on Actual Bridge]
    D --> E[Deflection, Vibration, and Strain Monitoring]
    E --> F[Data Correlation and Residual Life Estimation]

References: