Guidelines for Use of Silica-Fume in Rigid Pavement

IRC 114: Introduction - Key Points

IRC 114 focuses on the use of Silica Fume in Concrete for Rigid Pavements. The introduction sets the stage for understanding its impact on concrete properties and pavement performance.

Key Highlights:

• Silica Fume is a highly reactive pozzolanic material improving concrete strength and durability.
• Enhances abrasion resistance, crucial for rigid pavements.
• Influences both fresh concrete properties (workability, setting time) and hardened concrete properties (compressive strength, durability).
• The code references Indian Standards for specifications and testing methods.
• Emphasizes curing and opening to traffic guidelines to ensure performance.

Typical Specifications & Considerations:

Important Notes:

• Proper curing is critical for silica-fume concrete.
• Opening to traffic should be delayed until adequate strength is reached.
• Follow IS standards like IS 456 and IS 383 for complementary requirements.

flowchart TD
    A[Silica Fume Addition] --> B[Improved Concrete Properties]
    B --> C{Fresh Concrete}
    B --> D{Hardened Concrete}
    C --> E[Workability]
    C --> F[Setting Time]
    D --> G[Strength]
    D --> H[Durability & Abrasion Resistance]
    H --> I[Better Pavement Performance]

For detailed formulas and tables, refer to clauses 3-9 of IRC 114.

IRC 114 - Scope of Silica Fume Use in Concrete (Clause 4.5)

• Silica Fume Content: Up to 10% replacement by weight of cementitious materials (per IRC:15 for rigid pavement).
• Concrete Strength Requirements:
  • Minimum Flexural Strength: 4.5 MPa
  • Corresponding Compressive Strength: 40 MPa
• Benefits:
  • Highly cohesive concrete with low permeability.
  • Superior abrasion resistance.
  • Longer service life, ideal for coastal regions and high abrasion zones.

Key Specifications from IRC 114 & IS:15388

Abrasion Index (Australian Paving Association)

[ I_A = \frac{R}{P} ]

• I_A: Abrasion Index
• R: Ball race revolutions (thousands)
• P: Depth of wear (mm)

Recommended abrasion index for rigid pavements: 50

Curing & Opening to Traffic

• Minimum curing period: 16 days (wet hessian cloth or resin-based curing compound).
• Water for curing must be free from chlorides and sulphates.
• Pavement opening to traffic: After 28 days minimum.

flowchart TD
  A[Silica Fume Concrete Mix] --> B{Replacement % ≤ 10%?}
  B -- Yes --> C[Achieve 40 MPa Compressive Strength]
  C --> D[Low Permeability & High Abrasion Resistance]
  D --> E[Use in Coastal & High Abrasion

Influence of Silica-Fume on Fresh Concrete (IRC 114)

• Water Demand: Silica fume's very fine particles increase water demand. Use superplasticizers to maintain workability at low water-cement ratios.
• Minimum Water Content: Should not be less than 150 kg/m³ to avoid sticky mixes.
• Mixing: Use efficient pan or paddle mixers as per IS:4925 & IS:4926 for uniform dispersion.

Influence on Hardened Concrete

• Strength: Silica fume improves compressive and flexural strength (min flexural strength = 4.5 MPa, compressive strength = 40 MPa for PQC).
• Abrasion Resistance: Enhanced due to dense matrix and better aggregate bonding.
• Permeability: Reduced, leading to longer service life.

Abrasion Index (Australian Paving Association)

[ I_A = \frac{R}{P} ]

• (I_A) = Abrasion Index
• (R) = Ball race revolutions (thousands)
• (P) = Depth of wear (mm)

Silica Fume Specifications (IS:15388)

Curing & Opening to Traffic

• Minimum curing period: 16 days (wet hessian cloth + resin-based curing compound recommended).
• Opening to traffic after 28 days.

flowchart TD
    A[Silica Fume Addition] --> B[Increased Water Demand]
    B --> C[Use Superplasticizer]
    C --> D[Low Water-Cement Ratio]
    D --> E

Influence of Silica-Fume on Hardened Concrete (IRC 114)

Key Specifications:

• Silica-fume content: Up to 10% by weight of cementitious materials (IRC:15).
• Minimum Strengths for Pavement Quality Concrete (PQC):
  • Flexural strength ≥ 4.5 MPa
  • Compressive strength ≥ 40 MPa

Benefits:

• Increased compressive and flexural strength.
• Reduced permeability due to low water-cement ratio.
• Enhanced abrasion resistance (up to 100% improvement).
• Better bond between cement paste and aggregate, reducing wear.

Abrasion Index (Australian Paving Association)

[ I_A = \frac{R}{P} ]

• (I_A) = Abrasion Index
• (R) = Ball race revolutions (thousands)
• (P) = Depth of wear (mm)

Recommended Abrasion Index for Rigid Pavements:

• Minimum 50 for heavy pedestrian traffic and high wear areas.

Chemical & Physical Requirements of Silica-Fume (IS:15388)

Curing & Traffic Opening

• Curing duration: Minimum 16 days (wet hessian + curing compound).
• Opening to traffic: After 28 days minimum.

graph LR
A[Silica-Fume Addition (≤10%)] --> B[Reduced Water-Cement Ratio]
B --> C[Increased Strength & Durability]
C --> D[Abrasion Resistance ↑]
C --> E[Permeability ↓]
D --> F[Longer Service Life]

Summary: Use silica-fume up to 10% for high-strength, low-permeability concrete with superior abrasion resistance, especially suitable for

Abrasion Resistance of Silica-Fume Concrete (IRC 114 Highlights):

• Silica Fume Content: Up to 10% replacement by weight of cementitious materials (IRC:15).

• Strength Requirements:

  • Flexural strength ≥ 4.5 MPa
  • Compressive strength ≥ 40 MPa

• Abrasion Index (IA) Formula:
  [ IA = \frac{R}{P} ] Where:

  • ( R ) = Ball race revolutions (in thousands)
  • ( P ) = Depth of wear (mm)

• Recommended Abrasion Index for Pavements:

  Traffic Condition	Abrasion Index (IA)
  Busy footpaths/malls (heavy pedestrian)	51
  Public roadways	38
  Car parking & vehicular traffic	31

  • Guideline recommends IA = 50 for rigid pavements.

• Benefits:

  • High abrasion resistance (100%+ improvement with 10% silica fume)
  • Low permeability and cohesive concrete
  • Recommended for high wear areas: toll plazas, curves, steel-tyred vehicles, airfields.

• Curing:

  • Minimum 16 days curing
  • Use resin-based aluminized reflective curing compound + wet hessian cloth or manual moist curing.

• Chemical & Physical Requirements of Silica Fume (IS:15388):

  Property	Requirement
  SiO₂ content	≥ 85%
  Moisture content	≤ 3%
  Loss on ignition	≤ 4%
  Alkalis (Na₂O)	≤ 1.5%
  Specific surface	≥ 15 m²/gm (BET method)
  Oversize retained	≤ 10% on 45 micron sieve

flowchart LR
    A[Silica Fume Addition (up to 10%)] --> B[Low w/c ratio & Superplasticizer]
    B --> C[High Strength Concrete (≥40 MPa)]
    C --> D[Abrasion Resistance ↑ (IA

Key Stipulations in Indian Standards for Silica-Fume Concrete (IRC 114)

1. Silica-Fume Usage:

• Max 10% replacement by weight of cementitious materials (IRC:15, IS:15388).
• Used in high-performance concrete for rigid pavements and bridges (IRC:SP:70-2005).

2. Chemical Requirements (IS:15388):

3. Physical Requirements (IS:15388):

4. Concrete Strength:

• Minimum flexural strength: 4.5 MPa
• Corresponding compressive strength: 40 MPa

5. Curing Requirements (IRC:15):

• Minimum 16 days curing.
• Use resin-based aluminized reflective curing compound + wet hessian cloth or manual wet hessian curing.
• Water for curing must comply with IS:456 (free from chlorides/sulphates).

6. Opening to Traffic:

• Minimum 28 days before traffic use.

Abrasion Index (Australian Paving Association):

[ I_A = \frac{R}{P} ]

• (I_A) = Abrasion Index
• (R) = Ball race revolutions (thousands)
• (P) = Depth of wear (mm)

Recommended Abrasion Index for Pavements:

flowchart TD
    A[Sil

Key Specifications & Formulas for Curing as per IRC 114 & IRC:15

Curing Requirements:

• Start: Immediately after finishing operations.
• Methods:
  • Curing Compound + Wet Hessian Cloth: Resin-based aluminized reflective type curing compound applied, then wet hessian cloth spread and kept moist regularly.
  • Manual Wet Hessian Cloth: For small works, keep wet hessian cloth moist during curing.
• Duration: Minimum 16 days.
• Water Quality: Free from chlorides, sulphates, and injurious chemicals (as per IS:456).

Opening to Traffic:

• Minimum 28 days curing before opening to traffic.

Important Notes on Curing Compound

• Two applications allowed in arid areas with scarce water, combined with moist curing.
• Ensures prevention of rapid drying and proper hydration.

Summary Table for Curing

flowchart TD
    A[Concrete Placed & Finished] --> B{Start Curing Immediately}
    B --> C[Apply Resin-Based Curing Compound]
    C --> D[Spread Wet Hessian Cloth]
    D --> E[Keep Hessian Cloth Moist for 16 Days]
    B --> F[Manual Wet Hessian Cloth (Small Works)]
    E --> G[Prevent Rapid Drying & Ensure Hydration]
    G --> H[Open to Traffic After 28 Days]

This ensures proper hydration, strength gain, and durability of concrete pavements as per IRC guidelines.

IRC 114: Opening to Traffic - Key Points

The code section on Opening to Traffic (Clause 8) in IRC 114 relates to rigid pavements with silica-fume concrete. While the exact clause details are not provided, typical guidelines include:

General Specifications:

• Minimum curing period before opening to traffic: Usually 7 days for silica-fume concrete rigid pavements, ensuring adequate strength gain.
• Minimum compressive strength: Concrete should reach at least 70% of the specified characteristic strength before traffic loading.
• Abrasion resistance: Silica-fume concrete improves surface durability, aiding early opening.

Recommended Procedure:

1. Curing: Maintain moist curing for at least 7 days.
2. Strength Testing: Confirm compressive strength via cube/cylinder tests.
3. Load Restrictions: If early opening is necessary, restrict axle loads temporarily.

Typical Strength Gain Formula:

[ f_{c}(t) = f_{c28} \times \left(\frac{t}{28}\right)^{n} ]

• (f_{c}(t)) = compressive strength at age (t) days
• (f_{c28}) = 28-day compressive strength
• (n) ≈ 0.5 for silica-fume concrete

Summary Table (Indicative)

flowchart TD
    A[Concrete Placement] --> B[Curing (7 days)]
    B --> C[Strength Testing]
    C -->|≥ 70% strength| D[Open to Traffic]
    C -->|< 70% strength| E[Continue Curing]

Note: Verify with latest IRC 114 edition for precise values and conditions.

IRC 114: Recommendations for Use of Silica-Fume in Rigid Pavement

Key Points from IRC 114:

• Silica-Fume Dosage: Typically 5-10% by weight of cement.
• Effect on Fresh Concrete:
  • Increases cohesiveness and reduces bleeding.
  • Requires adjustment in water content or use of superplasticizers.
• Effect on Hardened Concrete:
  • Improves compressive strength by 15-30%.
  • Enhances durability and reduces permeability.
• Abrasion Resistance: Significantly improved, beneficial for rigid pavements subjected to traffic wear.
• Curing: Extended moist curing (7-14 days) recommended for optimum strength gain.
• Opening to Traffic: May be delayed slightly compared to normal concrete due to slower early-age strength gain.

Typical Mix Design Adjustments:

Formula: Adjusted Water Content

[ W_{adj} = W_{normal} - (SF \times \text{Water demand increase factor}) ]

Where:

• (SF) = Silica-fume content by weight of cement
• Water demand factor ≈ 0.1 to 0.15 (depends on SF fineness)

flowchart LR
    A[Fresh Concrete] --> B[Add Silica-Fume 5-10%]
    B --> C[Reduced Bleeding & Improved Cohesion]
    C --> D[Adjust Water Content / Superplasticizer]
    D --> E[Hardened Concrete]
    E --> F[Increased Strength & Durability]
    F --> G[Improved Abrasion Resistance]
    G --> H[Recommended Extended Curing]
    H --> I[Delayed Opening to Traffic]

Summary: Use 5-10% silica-fume by cement weight, reduce

IRC 114 - Key References, Formulas & Tables Summary

1. Silica Fume Usage in Concrete (Clause 4.5 & 9):

• Silica fume up to 10% by weight of cementitious materials (per IRC:15).
• Minimum flexural strength: 4.5 MPa
• Minimum compressive strength: 40 MPa
• Improves abrasion resistance, cohesion, and reduces permeability.

2. Abrasion Index (Australian Paving Association):

[ I_A = \frac{R}{P} ]

Where:

• (I_A) = Abrasion Index
• (R) = Ball race revolution (thousands)
• (P) = Depth of wear (mm)

Recommended abrasion index values:

3. Chemical Requirements of Silica-Fume (IS:15388):

4. Physical Requirements of Silica-Fume (IS:15388):

5. Curing & Opening to Traffic:

• Curing period: minimum 16 days (wet hessian or resin-based curing compound).
• Opening to traffic: minimum 28 days.

flowchart LR
    A[Silica Fume Concrete] --> B[Improved Strength & Durability]
    B --> C[Abrasion Resistance ↑]
    B --> D[Permeability ↓