Guidelines for Design and Construction of Continuously Reinforced Concrete Pavement (CRCP)
2015 Edition

IRC 118 Overview - Essential Highlights

• Coverage: Includes design, construction, and upkeep of Continuously Reinforced Concrete Pavements.
• Objective: Guidance on CRCP systems with or without elastic joints.
• Pavement Structure: Consists of reinforced concrete slab, sub-base, and subgrade layers.
• Design Emphasis: Focus on thickness, reinforcement detailing, joint types, shoulder design, and distress prevention.
• Authority: Developed under the Highways Specifications and Standards Committee (H-3).

Standard Pavement Structure (per IRC 118)

Key Design Elements:

• Thickness Design: Based on anticipated traffic and subgrade strength.
• Reinforcement: Longitudinal steel to regulate cracking and ensure load transfer.
• Joints: Types and intervals to manage crack patterns.

Summary Table (Excerpt)

Refer to Clauses 6 and 7 for detailed design formulas and examples.

flowchart TD
    Pavement --> ConcreteSlab
    Pavement --> Subbase
    Pavement --> Subgrade
    ConcreteSlab --> ReinforcementDesign
    ConcreteSlab --> ThicknessDesign
    ReinforcementDesign --> JointsAndLapping

Note: For exact design tables and formulas, see Clauses 6, 7, and 12.

Comparison Between CRCP with Elastic Joints and Jointless CRCP (IRC 118)

Elastic Joint Specifications (Clause 9)

• Joint fillers: Elastic bituminous or polymer-based materials.
• Dowel bars: Diameter 25-30 mm, length ~500 mm, spaced at 300 mm intervals.
• Joint width: 10-20 mm to accommodate expansion/contraction.

Visual Summary

flowchart LR
    JointlessCRCP --> NaturalCracks
    NaturalCracks --> LoadTransferSteel
    JointlessCRCP --> LowerMaintenance
    
    ElasticJointCRCP --> JointIntervals
    JointIntervals --> LoadTransferDowelBars
    JointIntervals --> ElasticFiller
    ElasticJointCRCP --> RequiresMaintenance

This differentiation informs design and upkeep strategies per IRC 118.

Strengths and Weaknesses of CRCP as per IRC 118

Advantages:

• Eliminates the need for transverse joints, reducing maintenance and joint-associated problems.
• Extends pavement lifespan due to enhanced load distribution.
• Decreases noise generated from vehicle wheel impacts.
• Well-suited for high-volume heavy traffic corridors.
• Minimizes water ingress and subgrade erosion.

Limitations (Clause 3.2):

• Unsuitable for marine environments unless corrosion-resistant steel is used.
• Difficulties in repairing underground utilities due to continuous slab.
• Not cost-effective for low-traffic or short-distance roads.
• Manual construction is slow and costly; mechanized methods are preferable.

Summary Table:

flowchart LR
    Advantages --> NoTransverseJoints
    Advantages --> LongerLife
    Advantages --> HeavyTrafficSuitability
    Advantages --> NoiseReduction
    Disadvantages --> CorrosionRisk
    Disadvantages --> RepairChallenges
    Disadvantages --> UnsuitableForLightTraffic
    Disadvantages --> ManualConstructionCost

These points assist in making informed decisions about CRCP application.

Typical Distress Types in CRCP (IRC 118)

• Longitudinal Cracks: Result from shrinkage and temperature variations.
• Transverse Cracks: Managed by continuous reinforcement; crack spacing and width minimized.
• Punchouts: Localized slab failures near transverse cracks due to support loss or stress concentrations.
• Edge Breaks: Occur along pavement edges; mitigated by proper shoulder design.
• Joint Failures: At designated construction, longitudinal, terminal, and transition joints.

Key Formula for Transverse Reinforcement Percentage (Pt):

[ P_t = \frac{Y_c \times W \times F}{2 \times f_s} \times 100 ]

Where:

• (P_t) = Percentage of transverse steel
• (Y_c) = Concrete unit weight (kN/m³)
• (W) = Pavement width (m)
• (F) = Base friction factor
• (f_s) = Permissible steel stress (75% of yield strength)

Friction Factors for Various Base Materials

Specifications:

• Maximum transverse bar spacing: 610 mm
• Minimum distance from transverse construction joints: 500 mm
• Shoulders should be full-depth concrete or tied jointed concrete to alleviate edge stresses and punchouts.

flowchart LR
    ShrinkageAndTemp --> LongitudinalCracks
    LongitudinalCracks --> TransverseReinforcementControlsCracks
    TransverseReinforcementControlsCracks --> Punchouts
    EdgeStress --> EdgeBreaks
    Joints --> JointFailures

This knowledge aids in designing durable CRCP pavements.

Typical Pavement Layering for CRCP According to IRC 118

• Subgrade:

  • Minimum thickness: 500 mm
  • Compaction: ≥ 97% Maximum Dry Density (IS 2720-Part 8)
  • Soaked CBR: ≥ 10% at 97% MDD
  • Uniform moisture and compaction critical for consistent support.

• Base Course:

  • Positioned below concrete slab; also called upper subbase.
  • Materials include:
    • Dry Lean Concrete (DLC), or
    • Dense Bituminous Layer (preferred to control erosion)
  • Granular or cement-treated bases possible but require stringent quality control.
  • A bituminous overlay on granular or cement-treated layers is recommended to reduce erosion.
  • Application of 5 mm non-woven geotextile on bituminous base enhances performance.

• Concrete Pavement Thickness:

  • Usually ranges from 250 mm to 300 mm depending on traffic.
  • Additional 10-15 mm added for wear and surface texture.
  • Thickness design follows IRC:58 without reductions for CRCP.

graph TD
    Subgrade --> BaseCourse
    BaseCourse --> ConcreteSlab
    BaseCourse --> ErosionControlLayer
    ErosionControlLayer --> ConcreteSlab

This stratification ensures structural strength and longevity.

Thickness Design Guidance for CRCP (IRC 118)

• Reference: IRC:58 is the governing standard for pavement thickness in India.
• Typical Thickness: Between 250 mm and 300 mm, adjusted for traffic intensity.
• Allowance: Add 10-15 mm thickness for surface wear and texturing.
• Notes:
  • CRCP thickness should not be reduced compared to jointed pavements.
  • Base course design is vital, preferably Dry Lean Concrete or dense bituminous layers to prevent erosion.
  • The use of a 5 mm non-woven geotextile over bituminous base layers may improve performance.

Summary Table

flowchart TD
    TrafficVolume --> ThicknessDecision
    ThicknessDecision -->|Low to Medium| Thickness250
    ThicknessDecision -->|High| Thickness300
    Thickness250 & Thickness300 --> AddWearAllowance
    AddWearAllowance --> FinalThickness
    FinalThickness --> BaseCourseDesign
    BaseCourseDesign --> OptionalGeotextile

This framework ensures a durable pavement base aligned with IRC norms.

Longitudinal Reinforcement Design as per IRC 118 Clauses 7.0 and 7.1.3

• Pavement Thickness (h): 300 mm (using M-40 grade concrete)
• Pavement Width (b): 7.0 m with a longitudinal joint
• Steel Percentage (ρ): 0.7%
• Steel Grade: Fe 500

Formula for Longitudinal Steel Area (As):

[ A_s = \rho \times b \times h ]

Where:

• (A_s) = Reinforcement area in mm²
• (\rho) = Steel ratio (decimal form, e.g., 0.007 for 0.7%)
• (b) = Pavement width in mm
• (h) = Pavement thickness in mm

Example Calculation:

[ A_s = 0.007 \times 7000 \times 300 = 14700 \text{ mm}^2 ]

Design Requirements:

• Employ Fe 500 grade steel bars.
• Place reinforcement longitudinally.
• Follow IRC:58 for thickness and joint design.
• Lap length and concrete cover as per IRC 118.

Summary Table

flowchart LR
    PavementWidth --> SteelAreaCalc
    PavementThickness --> SteelAreaCalc
    SteelAreaCalc --> SteelPercentage
    SteelPercentage --> SteelAreaFormula
    SteelAreaFormula --> SelectSteelGrade

This method ensures adequate longitudinal reinforcement for CRCP durability.

Shoulder Design Considerations in IRC 118 (Clause 8)

Shoulders play a critical role in supporting CRCP edges and minimizing punchouts.

• Types of Shoulders:

  • Full-depth concrete shoulders: Extensions of the main slab, common in US practice.
  • Tied jointed concrete shoulders: Plain or reinforced concrete with closely spaced transverse joints and tie rods linking to the main slab.

• Functions:

  • Reduce edge stresses on CRCP slabs.
  • Prevent large-scale punchouts.
  • Enhance structural support and safety along pavement edges.

• Construction Guidelines:

  • Full-depth shoulders offer the best edge stress reduction.
  • Transverse joint spacing in shoulders is shorter than in the mainline to reduce cracking.
  • Tie rods must connect shoulder slabs to the main pavement.

Shoulder Types Summary

Refer to Clauses 7 and 9 for detailed reinforcement and jointing specifications.

flowchart LR
    CRCP --> FullDepthShoulder
    CRCP --> TiedJointedShoulder
    TiedJointedShoulder --> ShortJoints
    TiedJointedShoulder --> TieRods
    FullDepthShoulder --> EdgeStressReduction
    TiedJointedShoulder --> EdgeStressReduction

Proper shoulder design enhances longevity and reduces maintenance.

IRC 118 Jointing Requirements for Continuously Reinforced Concrete Pavements

1. Longitudinal Joints (Clause 9.2)

• Continuous longitudinal reinforcement bars spanning the pavement width.
• Additional 2 m long bars positioned at transverse construction joints to maintain continuity.
• Longitudinal bars are tied to transverse bars using chairs.

2. Expansion Joints (Clause 9.4.1.1)

• Installed to accommodate thermal movements.
• Typically located at terminal and transition joints.
• Filled with compressible materials and sealed with joint sealants.

3. Transverse Construction Joints (Clause 9.1)

• Required when paving operations pause for over 30 minutes.
• Prepared using stop-end forms.
• Joints are grooved and sealed.
• Additional longitudinal bars of 2 m length placed between main bars.
• Transverse bars installed across the joint.

4. Transverse Reinforcement (Clauses 7.2 & Table 7.2)

[ P_t = \frac{Y_c \times W_s \times F}{2 f_s} \times 100 ]

Where:

• (P_t) = Percentage transverse steel
• (Y_c) = Concrete unit weight (kN/m³)
• (W_s) = Pavement width (m)
• (F) = Friction coefficient
• (f_s) = Allowable steel stress (75% of yield)

Maximum spacing: 610 mm

Minimum distance from transverse joints: 500 mm

5. Friction Coefficients for Base Layers

6. Shoulders

• Full-depth concrete or tied jointed plain/reinforced concrete.
• Connected to main slab with tie rods.
• Assist in reducing edge stresses and enhancing load transfer.

Lapping Requirements for Longitudinal Steel (IRC 118)

• Lap Length (L_lap):

[ L_{lap} = 35 \times d ]

Where d is the bar diameter.

• Important Rules:

  • Bars generally do not exceed 12 m, necessitating laps.
  • Laps must be staggered; no more than one-third of laps should occur in a single zone.
  • Minimum spacing between lap locations: 1.2 m to avoid weak planes.
  • Welding of TMT bars is discouraged; lap splicing is preferred.

• Rationale: Based on US research, 33 times bar diameter ensures sufficient bond; IRC 118 adopts a conservative 35 times multiplier.

Summary Table

flowchart LR
    BarLengthCheck --> ProvideLapSplice
    ProvideLapSplice --> CalculateLapLength
    CalculateLapLength --> StaggerLaps
    StaggerLaps --> LimitLapsAtLocation
    LimitLapsAtLocation --> MaintainSpacing
    MaintainSpacing --> AvoidWelding

This ensures structural continuity and bond integrity.

Construction Practices for CRCP (IRC 118 Clause 11.4)

• Restrictions on Vehicle Movement:

  • Dumpers and transit mixers must not travel directly over base course due to reinforcement.

• Concrete Delivery:

  • Employ conveyor belts or large transit mixers with side loading.
  • Side-tipping dumpers allowed if sufficient space is available.

• Paving Operations:

  • Similar to unreinforced concrete pavements, barring the above restrictions.
  • Refer to IRC:15 for comprehensive paving guidelines.

• Additional Notes:

  • Ensure reinforcement is properly aligned and tensioned prior to concrete placement.
  • Follow standard curing and compaction procedures.

flowchart LR
    MixPreparation --> TransportToSite
    TransportToSite --> SufficientSideSpace?
    SufficientSideSpace? -->|Yes| SideTippingDumpers
    SufficientSideSpace? -->|No| ConveyorOrLargeMixers
    SideTippingDumpers & ConveyorOrLargeMixers --> Paving
    Paving --> CompactionAndCuring

Refer to Clauses 6 and 7 for reinforcement and thickness design.

Illustrative Steel Design Example per IRC 118 (Clause 12)

While IRC 118 does not provide explicit example formulas in this section, the design follows principles from Clauses 7.1.3 and 12.1:

Core Formula for Longitudinal Steel Area (As):

[ A_s = \frac{M}{0.87 f_y z} ]

Where:

• (M) = Bending moment from traffic and temperature stresses
• (f_y) = Steel yield strength (typically 415 MPa)
• (z) = Lever arm (~0.95 times effective depth)

Steel Percentage Limits:

• Minimum: 0.12% (0.0012)
• Maximum: 1.5% (0.015)

Typical Design Steps:

1. Calculate moments.
2. Compute required steel area using the formula.
3. Verify steel percentage is within limits.
4. Choose bar sizes and spacing accordingly.
5. Ensure lapping and anchorage as per Clause 10.

Typical Values Table:

flowchart TD
    CalculateMoments --> DetermineSteelArea
    DetermineSteelArea --> CheckSteelLimits
    CheckSteelLimits -->|Within Limits| SelectBarsAndSpacing
    CheckSteelLimits -->|Outside Limits| ReviseDesign
    SelectBarsAndSpacing --> DetailLappingAnchorage

This framework ensures correct longitudinal reinforcement for CRCP longevity.

Summary of Key References and Formulas in IRC 118

1. Transverse Reinforcement Design (Clause 7.2)

• Transverse Steel Percentage (P_t):

[ P_t = \frac{Y_c \times W \times F}{2 \times f_s} \times 100 ]

Where:

• (Y_c) = Concrete unit weight (kN/m³)

• (W) = Pavement width (m)

• (F) = Friction factor of base layer

• (f_s) = Allowable steel stress (75% of yield strength)

• Bar Spacing: Maximum 610 mm

• Distance from Transverse Joints: Minimum 500 mm

2. Friction Factors for Base Materials

3. Shoulder Types

• Full-depth concrete shoulders matching main slab
• Tied jointed plain or reinforced concrete shoulders with short transverse joints
• Shoulders connected to main pavement with tie rods

4. Joint Categories

• Construction joints
• Longitudinal joints
• Terminal and transition joints

flowchart LR
    BaseLayer -->|Friction Factor| TransverseReinforcementDesign
    TransverseReinforcementDesign --> SteelPercentageCalculation
    SteelPercentageCalculation --> SpacingAndLocation
    SpacingAndLocation --> ShoulderDesign
    ShoulderDesign --> JointDesign

For in-depth longitudinal steel design and examples, consult Clause 12 and page 20 of IRC 118.