Guidelines for Use of Silica-Fume in Rigid Pavement
2013 Edition

IRC 114 Overview - Essential Insights

This code centers on the integration of silica-fume in rigid pavement concrete. The overview explains its role in boosting concrete's performance and pavement longevity.

Highlights:

• Silica-fume is a highly reactive pozzolan that improves strength and durability.
• Increases abrasion resistance, critical for rigid pavement applications.
• Affects both fresh concrete characteristics (such as workability and setting time) and hardened concrete properties (like compressive strength and durability).
• References Indian Standards for detailed specifications and testing.
• Stresses proper curing and guidelines for opening to traffic.

Typical Specification Parameters:

Important Notes:

• Adequate curing is essential for silica-fume concrete.
• Delay opening to traffic until sufficient strength is achieved.
• Follow IS standards such as IS 456 and IS 383 for complementary requirements.

flowchart TD
    A[Addition of Silica Fume] --> 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[Enhanced Pavement Performance]

Refer to clauses 3 to 9 in IRC 114 for detailed formulas and data tables.

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

• Replacement Level: Up to 10% by weight of cementitious materials as per IRC:15.
• Strength Criteria:
  • Minimum flexural strength: 4.5 MPa
  • Corresponding compressive strength: 40 MPa
• Advantages:
  • Produces cohesive concrete with low permeability.
  • Offers superior abrasion resistance.
  • Extends service life, especially suitable for coastal and high wear zones.

Specifications from IRC 114 and IS 15388

Abrasion Index (Australian Paving Association)

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

Where:

• (I_A) is the Abrasion Index
• (R) represents ball race revolutions in thousands
• (P) is the depth of wear in millimeters

Recommended abrasion index for rigid pavements is 50.

Curing and Traffic Opening

• Minimum curing period: 16 days using wet hessian cloth or resin-based curing compounds.
• Curing water must be free from chlorides and sulphates.
• Pavements should be opened to traffic only after a minimum of 28 days curing.

flowchart TD
  A[Concrete Mix with Silica Fume] --> B{Is Replacement ≤ 10%?}
  B -- Yes --> C[Achieve 40 MPa Compressive Strength]
  C --> D[Low Permeability and High Abrasion Resistance]
  D --> E[Suitable for Coastal and High Abrasion Areas]

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

• Water Requirement: Due to fine particle size, silica-fume increases water demand. Use of superplasticizers helps maintain workability at low water-cement ratios.
• Minimum Water Content: Should not be below 150 kg/m³ to prevent overly sticky mixes.
• Mixing Procedures: Employ efficient pan or paddle mixers conforming to IS:4925 and IS:4926 for uniform dispersion.

Hardened Concrete Effects

• Strength Gains: Enhances compressive and flexural strength (minimum flexural strength 4.5 MPa and compressive strength 40 MPa for pavement-quality concrete).
• Abrasion Resistance: Improved due to denser matrix and stronger aggregate-paste bond.
• Permeability: Considerably reduced, extending pavement lifespan.

Abrasion Index (Australian Paving Association)

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

Silica-Fume Requirements (IS 15388)

Curing and Traffic Opening

• Minimum curing period: 16 days (wet hessian cloth combined with resin-based curing compound recommended).
• Traffic opening after 28 days minimum.

flowchart TD
    A[Silica-Fume Addition] --> B[Higher Water Demand]
    B --> C[Use of Superplasticizer]
    C --> D[Low Water-Cement Ratio Maintained]
    D --> E[Enhanced Concrete Performance]

Effects on Hardened Concrete (IRC 114 Details)

Specifications:

• Silica-fume dosage up to 10% by cementitious material weight.
• Minimum flexural strength: 4.5 MPa.
• Minimum compressive strength: 40 MPa.

Advantages:

• Boosts both compressive and flexural strength.
• Reduces permeability through a low water-cement ratio.
• Significantly improves abrasion resistance (up to 100% increase).
• Enhances bond strength between cement paste and aggregates, minimizing wear.

Abrasion Index (Australian Paving Association)

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

• Recommended minimum abrasion index for rigid pavements: 50, suitable for heavy pedestrian traffic and high-wear zones.

Chemical and Physical Requirements of Silica-Fume (IS 15388)

Curing and Traffic Opening

• Minimum curing duration: 16 days using wet hessian cloth plus curing compound.
• Opening to traffic only after 28 days.

graph LR
A[Silica-Fume Addition (≤10%)] --> B[Lower Water-Cement Ratio]
B --> C[Increased Strength & Durability]
C --> D[Improved Abrasion Resistance]
C --> E[Reduced Permeability]
D --> F[Extended Pavement Lifespan]

Summary: Incorporating silica-fume up to 10% yields high-strength, low-permeability concrete with outstanding abrasion resistance, ideal for rigid pavements.

Abrasion Resistance Overview from IRC 114:

• Silica-fume can replace up to 10% of cementitious materials.
• Strength criteria include flexural strength ≥ 4.5 MPa and compressive strength ≥ 40 MPa.
• Abrasion Index (IA) is calculated as:

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

where R is ball race revolutions (thousands) and P is depth of wear (mm).

• Recommended abrasion index values:

• Benefits:

  • Abrasion resistance can improve by over 100% with 10% silica-fume.
  • Produces dense, cohesive concrete with low permeability.
  • Suitable for high-wear locations such as toll plazas, sharp curves, and airfield pavements.

• Curing Recommendations:

  • Minimum 16 days curing.
  • Use resin-based aluminized reflective curing compounds along with wet hessian cloth or manual moist curing.

• Chemical and Physical Standards (IS 15388):

flowchart LR
    A[Add Silica Fume (up to 10%)] --> B[Maintain Low Water-Cement Ratio with Superplasticizer]
    B --> C[Achieve High Strength (>40 MPa)]
    C --> D[Significant Increase in Abrasion Resistance]

Indian Standards Requirements for Silica-Fume Concrete (Based on IRC 114)

1. Silica-Fume Usage Limits:

• Maximum 10% replacement of cementitious materials (IRC:15, IS:15388).
• Applied in high-performance concrete for rigid pavements and bridge decks.

2. Chemical Specifications (IS 15388):

3. Physical Properties (IS 15388):

4. Concrete Strength Requirements:

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

5. Curing Guidelines (IRC:15):

• Minimum curing period of 16 days.
• Use of resin-based aluminized reflective curing compounds combined with wet hessian cloth or manual wet curing.
• Curing water must comply with IS:456, free from chlorides and sulphates.

6. Traffic Opening:

• Minimum 28-day curing before allowing traffic.

Abrasion Index (Australian Paving Association):

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

flowchart TD
  A[Silica-Fume Concrete] --> B[Meets Chemical & Physical IS Standards]
  B --> C[High Strength & Durability]
  C --> D[Suitable for Traffic Loads]

Curing Specifications as per IRC 114 and IRC:15

Curing Protocol:

• Initiation: Begin immediately after finishing the concrete surface.
• Approved Methods:
  1. Application of a resin-based aluminized reflective curing compound followed by spreading wet hessian cloth maintained moist throughout curing.
  2. For smaller projects, manual application and maintenance of wet hessian cloth moisture.
• Duration: Minimum 16 days.
• Water Quality: Use curing water free from harmful chemicals such as chlorides and sulphates, conforming to IS 456.

Opening to Traffic:

• Traffic should not be allowed before 28 days of curing.

Notes on Curing Compound Usage

• In arid regions with water scarcity, two applications of curing compound combined with moist hessian curing are permissible.
• Proper curing prevents rapid moisture loss and ensures adequate hydration.

Summary Table

flowchart TD
    A[Concrete Placement & Finishing] --> B[Start Curing Immediately]
    B --> C[Apply Resin-Based Curing Compound]
    C --> D[Spread Wet Hessian Cloth]
    D --> E[Maintain Moisture for 16 Days]
    B --> F[Manual Wet Hessian for Small Works]
    E --> G[Prevent Drying & Ensure Hydration]
    G --> H[Open to Traffic After 28 Days]

This curing regimen ensures proper hydration, strength development, and durability of silica-fume concrete pavements.

IRC 114 Guidance on Opening Rigid Pavements to Traffic

This section addresses traffic opening for rigid pavements made with silica-fume concrete.

General Recommendations:

• Minimum curing before traffic: Generally 7 days moist curing is necessary to attain sufficient strength.
• Strength requirement: Concrete should reach at least 70% of specified design compressive strength before loading.
• Abrasion resistance: Improved by silica-fume, facilitating earlier traffic opening.

Suggested Procedure:

1. Maintain moist curing for minimum 7 days.
2. Conduct compressive strength testing (cube or cylinder).
3. If early opening is unavoidable, implement temporary axle load restrictions.

Strength Gain Estimation Formula:

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

• (f_c(t)) is compressive strength at age t days
• (f_{c28}) is 28-day compressive strength
• (n) is approximately 0.5 for silica-fume concrete

Summary Table

flowchart TD
    A[Concrete Placement] --> B[Curing for 7 Days]
    B --> C[Strength Testing]
    C -->|≥ 70% Strength| D[Permit Traffic Opening]
    C -->|< 70% Strength| E[Continue Curing]

Note: Verify current IRC 114 edition for precise parameters and procedures.

Recommendations in IRC 114 for Silica-Fume Usage

Key Highlights:

• Dosage: Typically between 5% to 10% by cement weight.
• Fresh Concrete Effects:
  • Increases cohesiveness and decreases bleeding.
  • Requires adjustments in water content or use of superplasticizers.
• Hardened Concrete Benefits:
  • Raises compressive strength by 15% to 30%.
  • Enhances durability and lowers permeability.
• Abrasion Resistance: Significantly increased, ideal for pavements exposed to heavy traffic wear.
• Curing: Extended moist curing (7 to 14 days) is advised for optimal strength.
• Traffic Opening: May need to be postponed slightly compared to conventional concrete due to slower early strength gain.

Typical Mix Design Adjustments:

Adjusted Water Content Formula

[ W_{adj} = W_{normal} - (SF \times \text{Water Demand Factor}) ]

Where:

• (SF) is silica-fume content by cement weight
• Water demand factor ranges between 0.1 to 0.15 depending on silica-fume fineness

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

Summary: Silica-fume addition between 5% and 10% improves strength and abrasion resistance but requires mix adjustments and longer curing.

Summary of Key References, Formulas, and Tables in IRC 114

1. Silica-Fume Usage (Clauses 4.5 & 9):

• Up to 10% replacement of cementitious materials.
• Minimum flexural strength: 4.5 MPa.
• Minimum compressive strength: 40 MPa.
• Enhances abrasion resistance and reduces permeability.

2. Abrasion Index Formula (Australian Paving Association):

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

Where:

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

Recommended abrasion index values:

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

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

5. Curing and Traffic Opening:

• Minimum curing duration: 16 days (wet hessian or resin-based curing).
• Minimum traffic opening period: 28 days.

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