Guidelines for Corrosion Prevention, Monitoring and Remedial Measures for Concrete Bridge Structures

IRC SP 80 - Scope: Key Specifications & Tables Summary

Scope Overview:

• Guidelines for corrosion control in concrete bridges.
• Applies to new and existing bridges after repair/rehabilitation.
• Covers design, detailing, materials, construction, and protective coatings.

Key Formulas & Limits

Concrete & Materials

• Use dense concrete with low water-cement ratio.
• Mineral admixtures (fly ash, silica fume, GGBS) improve durability.
• Cement content and curing critical for corrosion resistance.
• Aggregates per IS:383-1995 and IS:456-2000.
• Chemical admixtures must be compatible and controlled.

Protective Coatings (Example: Acrylic Elastomeric)

• Surface prep: clean, sound, free of laitance/oil.
• Coating applied after primer with 2-72 hours interval.
• Performance guarantee: minimum 5 years recommended.

Detailing & Construction

• Minimize expansion joints; prefer continuous decks.
• Waterproof membranes below deck wearing coat.
• Sloped pier caps to avoid water ponding.
• Use leak-proof joints and protect cable ducts.
• Bearings accessible for inspection/replacement.

flowchart TD
    A[Design Stage] --> B[Control Crack Width & Cover]
    B --> C[Material Selection]
    C --> D[Concrete Mix & Admixtures]
    D

IRC SP 80: Terminology and Definitions - Key Specifications & Tables

While the code does not provide a dedicated clause on Terminology and Definitions, relevant key parameters for corrosion control and repair are summarized below from related clauses:

1. Design Stage: Corrosion Control Parameters (Table 5.1)

2. Quality Control Tests for Coatings (Table 6.9)

3. Remedies for Concrete Defects (Table 6.10.2)

Causes and Mechanisms of Corrosion (IRC SP 80)

1. Corrosion Cell (Fig. 3.1) & Local Cell Theory:

   • Corrosion occurs due to electrochemical cells formed on steel surfaces.
   • Variations in metallurgy (cold working, impurities) create local anodic and cathodic areas on the same bar → "Local Cell Theory."
   • Corrosion current density (Amp/cm²) quantifies corrosion rate.
   • Metal loss can also be expressed as mils/year or mg/cm²/day (mdd).

2. Corrosion Products & Volume Expansion (Fig. 3.2b):

   • Iron oxides/hydroxides occupy larger volume than original steel → causes cracking and spalling of concrete cover.

3. Types of Corrosion:

   • Uniform corrosion: Even surface loss.
   • Localized corrosion: Pitting, crevice corrosion (at joints, bolts).
   • Galvanic corrosion: Between dissimilar metals (e.g., steel-aluminum).
   • Pitting corrosion: Localized holes due to surface heterogeneity.
   • Crevice corrosion: In confined spaces with dirt/salts.
   • Exfoliation, Stress corrosion cracking, Hydrogen embrittlement: Advanced forms affecting durability.

4. Corrosion Rate Formula (simplified):

[ \text{Corrosion rate} = \frac{K \times I_{\text{corr}} \times EW}{\rho \times A} ]

Where:

• (I_{\text{corr}}) = corrosion current (A)
• (EW) = equivalent weight of steel
• (\rho) = density of steel
• (A) = exposed area (cm²)
• (K) = constant depending on units

5. Design Control Measures (Table 5.1):

flowchart LR

Materials for Corrosion Protection (IRC SP 80 - Clause 5.5 & related)

Key Specifications & Tables:

1. Crack Width Control (Table 5.1)

• Crack width under sustained loads:
  • Severe exposure: ≤ 0.2 mm
  • Moderate exposure: ≤ 0.3 mm
• Achieved by controlling bar diameter and spacing (max 200 mm spacing).

2. Concrete Cover (Table 5.1)

3. Corrosion Control Methods (Table 5.3)

• Use dense, impermeable concrete with low water-cement ratio.
• Use mineral admixtures: fly ash, silica fume, GGBS to reduce permeability.
• Use sulphate resistant cement in sulphate environments.
• Use coatings (epoxy, chlorinated rubber) for aggressive chemicals.
• Use galvanized or epoxy-coated steel reinforcement.
• Grout prestressing tendons fully with zero bleeding grout.

4. Galvanizing Zinc Coating (Table 6.1)

Additional Recommendations:

• Use waterproofing membranes below deck wearing coat.
• Provide sloped pier caps to avoid water ponding.
• Use integral structures to minimize joints.
• Avoid chloride contamination on galvanized bars.
• Use chemical admixtures compatible with cement.
• Ensure good curing to improve corrosion resistance by 12x.

flowchart TD
    A[Design Stage] --> B[Control Crack Width ≤ 0.2 mm]
    A --> C[Provide Adequate Cover (40-50 mm)]
    A --> D[Use Dense Concrete with Low w/c Ratio]
    D --> E[Add Mineral Admixtures (Fly Ash, GGBS)]
    A

Design Considerations for Corrosion Prevention (IRC SP 80, Clause 5.5 & related)

Key Parameters & Requirements (Table 5.1 summary)

Design & Detailing Guidelines

• Crack control: Use well-distributed steel with spacing ≤ 200 mm; control bar diameters and spacing to limit crack width.
• Minimize expansion joints: Prefer continuous decks to reduce water ingress.
• Pre-cast construction: Preferred for quality control.
• Integral structures: Reduce joints and leakage.
• Slope pier caps and provide waterproof membranes under decks.
• Protect cables and ducts with grouting and HDPE sheathing.
• Provide drainage to avoid water accumulation on components.

Concrete & Materials

• Use dense concrete with low water-cement ratio (w/c) and adequate cement content.
• Incorporate mineral admixtures like fly ash, silica fumes, GGBS to reduce permeability and chloride diffusion.
• Proper curing improves corrosion resistance significantly.
• Use coated or galvanized steel for additional protection.
• Avoid harmful water impurities.

Crack Width Formula (IRC 21 Appendix-I, simplified)

[ w = \beta \times \varepsilon_{sm} \times d ]

• (w) = crack width (mm)
• (\beta) = coefficient depending on bar arrangement
• (\varepsilon_{sm}) = average strain in reinforcement
• (d) = effective cover depth

Summary Flowchart of Corrosion Prevention Design

flowchart TD
    A[Design Stage] --> B{Control Crack Width}
    B -->|Yes| C[Limit crack width ≤ 0.2-0.3 mm]
    B -->|No| D[Use distributed reinforcement ≤ 200

Protective Coatings & Surface Treatments (IRC SP 80 Highlights)

1. Acrylic Elastomeric Coating (Clause 1.5)

• Dry Film Thickness (DFT): 200-225 microns (min. 2 coats)
• Consumption: 400-450 gm/m² (2 coats)
• Primer:
  • Single component acrylic resin dispersion
  • Coverage: 75-100 gm/m²
  • Air curing ~60 min
• Properties:
  • CO₂ diffusion resistance: Equivalent air layer thickness > 50 m (DIN 53122 Part-I)
  • Water vapor diffusion resistance: Equivalent air layer thickness < 4 m
  • Waterproofing: ≥ 50% flux reduction
• Application: Surface must be clean, free from laitance, oil, grease; pinholes filled with polymer mortar.
• Coating: 2 coats, 2-72 h interval, wet film thickness measured by gauge.

2. Epoxy Polyurethane Painting System (Clause 6.5.2)

• Coats: 4 coats (Primer, Middle, Top - epoxy; Finish - polyurethane)
• Typical DFT:

• Surface: Clean, matured concrete (≥28 days)
• Curing: As per manufacturer's specs, 24 h between coats

3. Quality Control Tests (Clause 6.7)

4

Corrosion Monitoring & Assessment - IRC SP 80 Key Points

1. Design Stage Corrosion Control (Table 5.1)

• Crack width control limits ingress of corrosive agents.
• Adequate cover protects reinforcement from environmental exposure.

2. Corrosion Risk Assessment by Resistivity Mapping (Clause 7.2, Table 7.2)

• Systematic resistivity surveys over grid points identify corrosion-prone zones.
• Lower resistivity indicates higher corrosion risk due to moisture and ionic presence.

Summary Diagram: Corrosion Risk vs Resistivity

graph LR
    A[> 20,000 ohm-cm] -->|Negligible| B[Low Corrosion Risk]
    C[10,000 - 20,000 ohm-cm] -->|Low| B
    D[5,000 - 10,000 ohm-cm] -->|High| E[High Corrosion Risk]
    F[< 5,000 ohm-cm] -->|Very High| G[Very High Corrosion Risk]

Use these parameters and resistivity mapping to design, monitor, and assess corrosion in concrete bridge structures effectively.

Remedial and Strengthening Measures — IRC SP 80 Summary

1. Corrosion Control (Clause 5.5, Table 5.1)

• Crack Width Limits:
  • Severe exposure: ≤ 0.2 mm
  • Moderate exposure: ≤ 0.3 mm
• Clear Cover for Reinforcement (mm):
  • Moderate: 40
  • Severe: 50
  • Wetting & Drying zone: 75

2. Remedies for Concrete Defects (Clause 6.10.2)

3. Remedies for Corrosion of Steel (Clause 6.10.3)

• Preserving Passivity: Increase cover, replace carbonated concrete, electrochemical re-alkalization.
• Increasing Resistivity: Surface treatments to control moisture.
• Cathodic Control: Limit oxygen, apply coatings.
• Cathodic Protection: Apply electrical potential.
• Anodic Control: Coatings, inhibitors on reinforcement.

Key Formula for Crack Width Control (IRC 21-2000)

[ w_k = \beta \times \epsilon_{sm} \times d_{eff} ]

Where:

• (w_k) = Crack width
• (\epsilon_{sm}) = Average strain in reinforcement
• (d_{eff}) = Effective depth
• (\beta) = Coefficient depending on exposure and loading

Diagram: Remedial Measures Flow

flowchart TD
    A[Identify Problem] --> B{Type of Defect}
    B --> C[Concrete Defects]
    B --> D[Steel Corrosion]
    C --> E[Impregnation/Coating]
    C --> F[Crack Sealing]
    C --> G[Concrete Restoration]
    C

IRC SP 80: Quality Control & Testing Procedures Summary

1. Tests on Coating Systems (Table 6.7)

2. Key Tests on Fusion Bonded Epoxy Coating (Clause 6.3)

3. General Quality Control Notes

• Manufacturer certificates per ASTM/IS standards must be furnished.
• Use Elcometer for dry film thickness and uniformity.
• Adhesion tests as per IS:13620

Handling and Storage of Pre-stressing Materials (IRC SP 80 & related IRC/IS codes)

Key Specifications & Practices:

• Minimum Clear Cover for Pre-stressing Steel:

  • 75 mm minimum clear cover measured from outside of sheathing to concrete surface.
  • Minimum clear spacing between cables: 50 mm or duct diameter, whichever is greater.
    (IRC:18-2000 Clause 16.1, 16.3)

• Grouping of Cables:

  • Avoid grouping; if unavoidable, only vertical grouping up to 2 cables permitted.
  • No grouping in severe exposure conditions.
    (IRC:18-2000 Clause 16.4)

• Sheathing:

  • Use corrugated HDPE ducts for corrosion resistance and chloride/sulphate barrier.
  • Metallic ducts may be manufactured onsite to reduce storage corrosion risks.
  • Apply washable water-soluble oil or Vapour Phase Inhibitors (VPI) on outer surfaces for temporary corrosion protection.

• Storage & Handling:

  • Store pre-stressing steel (strands/wires, anchorages, ducts, couplers) in clean, dry, covered areas.
  • Wrap steel with gunny/plastic covers to avoid moisture and contaminants.
  • Avoid contact with sulphur or other corrosive materials during transport.
  • Temporary corrosion protection via phosphate/lubricant layers and soluble oils; reapply if needed.
  • VPI chemicals (e.g., beta-naphthal dinitro benzene) can be blown into sheathing ducts for protection.

• Curing:

  • Concrete with pre-stressing steel should be cured for at least 14 days to ensure durability.

Corrosion Control Summary Table (Extract):

Key Specifications & Formulas for Anchorage and Sheathing Protection (IRC SP 80)

1. Clear Cover for Reinforcement & Pre-stressing Steel

Cover may be reduced by 5 mm for factory-made precast products with quality assurance.

2. Grouping of Cables

• Avoid grouping; if unavoidable, only vertical grouping of max 2 cables allowed.
• No grouping in severe exposure.
• Use high capacity strands to minimize grouping.
• IRC:18-2000 Clause 16.4

3. Sheathing Material

• Use Corrugated HDPE ducts for watertight, abrasion-resistant protection.
• Metallic ducts may be site-fabricated to avoid long storage corrosion.
• Outer surface coated with washable water-soluble oil or Vapour Phase Inhibitor (VPI) powder.
• Ducts must be continuous, free from pinholes.
• HDPE preferred for flexibility and low embrittlement; polypropylene for thermal stability.

4. Protection of Tendons

• Unbonded tendons: Use anti-corrosive grease meeting:

Moisture Control in Concrete (IRC SP 80 & related IRC codes):

Key Methods (Clause 1.1)

• Impregnation: Penetrating liquids block concrete pores.
• Surface Coating: Crack bridging or non-bridging coatings.
• Crack Sealing/Filling: Prevent moisture ingress.
• Conversion of Cracks to Joints: Controls crack propagation.
• External Cladding: Physical barrier.
• Membranes: Waterproof surface layers.

Design Stage (Clause 5.5, IRC 21-2000)

Material Specifications

• Aggregates: Clean, natural, max 20 mm size.
• Water: Limits on organics (200 mg/l), sulphates (400 mg/l), chlorides (500 mg/l RCC).
• Reinforcement: Grades S-240, S-415, S-500; coated bars recommended.
• Sheathing: Corrugated HDPE ducts to block chlorides/sulphates.

Construction Stage

• Curing: Minimum 14 days; steam curing recommended.
• Handling: Protect prestressing materials from moisture.

Formula for Crack Width Control (IRC 21-2000 Appendix-1)

[ \text{Average strain} \leq 0 \quad \Rightarrow \quad \text{Crack width} \leq 0.2 \text{ mm (severe)} \quad \text{or} \quad

Environmental Exposure & Durability: Key Formulas & Specifications (IRC SP 80)

1. Crack Width Limits (Clause 5.5, IRC:21-2000)

• Maximum crack width under sustained loads:
  • Severe exposure: 0.2 mm
  • Moderate exposure: 0.3 mm

2. Clear Cover for Reinforcement (IRC:21-2000 Clause 303.4.3)

• Pre-stressing steel cover: Minimum 75 mm from sheathing
• Cable spacing: Minimum 50 mm or duct diameter (whichever is greater)

3. Concrete Mix & Materials

4. Protective Coatings

• Acrylic Elastomeric Coating (Clause 6.5.1)
  • Dry Film Thickness (DFT): **

IRC SP 80: Case Studies & Typical Crack Patterns — Key Points

Crack Width Limits (Clause 5.5, Table 5.1)

• Severe Exposure: Max crack width = 0.2 mm
• Moderate Exposure: Max crack width = 0.3 mm
• Crack width under sustained loads should comply with specified formulas ensuring average strain is negative.

Clear Cover for Reinforcement (Table 5.1)

Typical Crack Types (Clause 7.3)

• Plastic settlement/shrinkage cracks: Within hours after setting; cause bond loss.
• Thermal contraction cracks: Weeks after; due to heat in thick elements.
• Drying shrinkage cracks: Weeks to years; moisture loss.
• Corrosion cracks: Months to years; at corners/edges, leading to concrete deterioration.
• Alkali-aggregate cracks: Months to years; internal bursting due to alkali reaction.
• Frost damage, sulphate attack, salt weathering: Long-term degradation mechanisms.

Crack Pattern Assessment & Remedies

• Visual inspection critical: look for spalling, rust stains, deformation.
• Remedies include crack sealing, surface coatings, impregnation, and structural strengthening (Table 6.8 & 6.9).
• For corrosion cracks, maintain crack width limits and adequate cover.

Formula for Crack Width Control (per IRC 21-2000 Appendix 1)

[ w = \beta \times \epsilon_{sm} \times d_{eff} ]

• (w) = crack width (mm)
• (\beta) = coefficient depending on bar arrangement
• (\epsilon_{sm}) = mean strain in reinforcement under sustained load
• (d_{eff}) = effective cover or distance to tension face (mm)

graph TB
A[Crack Causes] --> B[Plastic Settlement]
A --> C[Thermal Contraction]
A --> D[Drying Shrinkage]
A --> E[Corrosion]
A --> F[Alkali-Aggregate]
A --> G[Frost Damage]
A --> H[Sulphate Attack]
A --> I[

IRC SP 80: References and Standards Summary

Key Specifications for Corrosion Control (Clause 5.5 & related)

Quality Control Tests for Coating Systems (Clause 6.7, Table 6.9)

Additional Design & Material Notes

• Crack Control: Use well-distributed reinforcement with spacing ≤ 200 mm to limit crack width