Guidelines for the Structural Evaluation of Rigid Pavement by Falling Weight Deflectometer (without CD)

IRC 117: Introduction - Key Specifications & Formulas

Overview

• IRC 117 covers evaluation of rigid pavements using Falling Weight Deflectometer (FWD) and Load Transfer Efficiency (LTE).
• LTE assesses joint condition by comparing deflections on loaded and unloaded slabs.
• FWD test evaluates pavement slab strength and subgrade modulus.

Key Formulas

Load Transfer Efficiency (LTE):

[ LTE = \frac{\text{Deflection of unloaded slab}}{\text{Deflection of loaded slab}} \times 100% ]

Typical LTE Values (From Appendix IV)

High LTE (>95%) indicates good joint condition.

FWD Evaluation Parameters (Appendix V)

Summary Diagram: LTE & FWD Testing Workflow

flowchart TD
    A[FWD Test Setup] --> B[Apply Load via Loading Plate]
    B --> C[Measure Deflections at 0, 300, 600, 900 mm]
    C --> D[Calculate LTE using Loaded & Unloaded Deflections]
    C --> E[Calculate Modulus of Subgrade & Concrete]
    D --> F[Assess Joint Condition]
    E --> G[Assess Pavement Strength]

References

Key Formulas & Specifications for FWD Testing & Calibration (IRC 117):

1. Calibration of FWD (Clause 5.5)

• FWD must be calibrated as per IRC:115-2014 for reproducible results.
• Calibration includes verifying load and deflection sensors accuracy.

2. Load Transfer Efficiency (LTE) Calculation (Appendix IV)

[ \text{LTE} = \frac{\text{Unloaded Slab Deflection}}{\text{Loaded Slab Deflection}} \times 100% ]

• Typical LTE values from tests on Delhi-Mathura Road range 97% to 99.5%, indicating good joint condition.
• Loading plate diameter = 300 mm
• Sensor spacing = 200 mm

3. Pavement Evaluation Process (Clause 6.3 & Appendix V)

Stepwise evaluation of subgrade modulus (k), concrete modulus (E), and flexural strength (f):

• Measure deflections at 0, 300, 600, 900 mm from load center.
• Calculate Area of Deflection Basin (A):

[ A = 6 \times [D_0 + 2(D_1 + D_2 + D_3)]^2 ]

Where:

• (D_0, D_1, D_2, D_3) = deflections at 0, 300, 600, 900 mm (mm)

• Calculate Radius of Relative Stiffness (l):

[ l = \sqrt[4]{\frac{E h^3}{12k(1-\mu^2)}} ]

Where:

• (E) = Elastic modulus of concrete (MPa)
• (h) = Pavement thickness (mm)
• (k) = Modulus of subgrade reaction (MPa/m)
• (\mu) = Poisson's ratio of concrete (typically 0.15)

4. Example (Appendix III):

Pavement Deflection Measurement & Analysis (IRC 117 Key Points)

1. Load Transfer Efficiency (LTE) at Transverse Joints

Measured by FWD with:

• Loading plate diameter = 300 mm
• Sensors spaced 200 mm apart
• LTE formula:
  [ LTE = \frac{\text{Unloaded slab deflection}}{\text{Loaded slab deflection}} \times 100% ]
• Typical LTE values from tests: ~97% to 99% (good condition)

2. Deflection Basin Area (A) Calculation

[ A = 6 \times \left[ D_0 + 2(D_1 + D_2 + D_3) \right]^2 ]
Where:

• (D_0, D_1, D_2, D_3) = Deflections at 0, 300, 600, 900 mm from load center (mm)

3. Radius of Relative Stiffness (l)

• Derived from charts or formulas (excel sheet available)
• Used to characterize pavement stiffness

4. Subgrade Modulus (k) (MPa/m) & Elastic Modulus of Concrete (E_c) (MPa)

For Winkler foundation (liquid type):
[ k = \text{Function of normalized deflections and } l ]

Elastic modulus of concrete:
[ E_c = 1000 \times h^3 \times \frac{P}{l^4} \times \frac{1 - \mu_c^2}{k} ]
Where:

• (h) = slab thickness (mm)
• (P) = applied load (kN)
• (\mu_c) = Poisson’s ratio of concrete (~0.15)
• (l) = radius of relative stiffness (mm)

5. Concrete Strength from Elastic Modulus

[ f_{ck} = \left(\frac{E_c}{5000}\right)^{0.5} \quad \text{(MPa)} ]

Flexural strength:
[ f_{mr} = 0.7 \times f_{ck}^{0.5} \quad \text

Axle Load Spectrum & Effects (IRC 117)

Key Points from IRC 117 (Clauses 4.2 & 5.2):

• Axle Load Classes:

  • Single axle: 10 kN increments
  • Tandem axle: 20 kN increments
  • Tridem axle: 30 kN increments

• Legal axle load limits (India):

  • Single axle: 10.2 tonnes (~100 kN)
  • Tandem axle: 18 tonnes (~180 kN)
  • Tridem axle: 24 tonnes (~240 kN)

• Axle Load Spectrum Table (Example for Single Axle):

• Cumulative Number of Axles (Fatigue Damage):

[ C = 365 \times A \times \frac{(1 + r)^n - 1}{r} ]

Where:

• (C) = cumulative axles till evaluation

• (A) = initial axles/day

• (r) = annual growth rate (decimal)

• (n) = years since construction

• Fatigue Damage Analysis: Axle loads are categorized by weight intervals (Table 1) and repetitions are used to estimate pavement fatigue life.

Effects on Pavement:

• Heavy axle loads cause:

  • High flexural stresses → fatigue cracking
  • High subgrade pressure → permanent deformation

• Buses/light vehicles are excluded from fatigue damage calculations.

Summary Diagram:

flowchart LR
    A[Axle Load Survey] --> B[Load Categorization: Single, Tandem, Tridem]
    B --> C[Tabulation of Axle Load Spectrum]
    C --> D[Calculate Cumulative Axle Repetitions (C)]
    D --> E[Fatigue Damage Analysis]
    E --> F[Pavement Remaining Life Estimation]

Use IRC:58-2011 for detailed axle load intervals and IRC:117 for fatigue damage evaluation methodology.

IRC 117 - FWD Load Application & Deflection Data Acquisition

Key Formulas:

1. Deflection Basin Area (A):
   [ A = 6 \times \left( D_0 + 2(D_1 + D_2 + D_3) \right)^2 ]
   Where:

• (D_0, D_1, D_2, D_3) = Deflections at 0, 300, 600, 900 mm from load center (mm)

2. Load Transfer Efficiency (LTE %):
   [ LTE = \frac{\text{Unloaded Slab Deflection}}{\text{Loaded Slab Deflection}} \times 100 ]

Typical Data from IRC 117 (FWD Plate Dia = 300 mm):

Evaluation Procedure (Clause 6.3):

• Measure deflections at 0, 300, 600, 900 mm from load center.
• Use deflections and load to compute:
  • Modulus of Subgrade Reaction (k) for Winkler foundation.
  • Elastic Modulus of Concrete (E).
  • Flexural Strength (f_r) of pavement slab.

Example Output for 300 mm Thick Slab, Load = 50 kN:

Pavement Evaluation Process (IRC 117)

Key Components:

• Falling Weight Deflectometer (FWD):
  Used to measure pavement deflections under load to assess structural capacity.

• Load Transfer Efficiency (LTE):
  Evaluates joint performance by comparing deflections on loaded and unloaded slabs.

Load Transfer Efficiency (LTE) Formula:

[ \text{LTE} = \frac{\text{Deflection of Unloaded Slab}}{\text{Deflection of Loaded Slab}} \times 100% ]

Sample LTE Data (Target Impact Load 5500 kg):

High LTE (>95%) indicates good joint condition.

Pavement Strength & Subgrade Modulus Evaluation (Appendix V):

Inputs from FWD:

• Deflections at 0, 300, 600, 900 mm from load center
• Load (P), loading plate radius (a)
• Slab thickness (h)
• Poisson's ratios: Concrete = 0.15, Subgrade = 0.45

Outputs:

Summary Flowchart of Pavement Evaluation:

flowchart TD
    A[FWD Test Setup] --> B[Measure Deflections]
    B --> C[Calculate LTE]
    B --> D[Calculate Modulus of Subgrade & Concrete]
    C --> E{LTE > 95%?}

IRC 117 - Surface Temperature Measurement During Testing

Key Points from Clause 6.2:

• Preferred Method: Record pavement temperature from embedded temperature holes during FWD testing (research projects).
• Practical Method: Measure surface temperature at each test location using an infrared (IR) thermometer during production-level testing.
• FWD Equipment:
  • If equipped with IR thermometer, FWD automatically records surface temperature.
  • If not, use a handheld IR thermometer and manually record temperature.
• Temperature Limit: Suspend testing if pavement surface temperature exceeds 40°C to ensure data reliability.

Summary Table for Surface Temperature Measurement

Practical Notes:

• Surface temperature affects pavement stiffness and deflection.
• Accurate temperature measurement ensures valid FWD test results.
• Use consistent measurement technique and timing to minimize variability.

flowchart TD
    A[FWD Test Start] --> B{Is FWD equipped with IR thermometer?}
    B -- Yes --> C[Auto record surface temperature]
    B -- No --> D[Operator measures temperature with handheld IR thermometer]
    C & D --> E{Is surface temp > 40°C?}
    E -- Yes --> F[Suspend testing]
    E -- No --> G[Continue testing]

This approach aligns with IRC 117 recommendations for reliable pavement evaluation during FWD testing.

IRC 117: Detection and Filling of Voids Underneath Rigid Pavement

Key Points from IRC 117

• Detection of Voids:

  • Perform regular inspections every 3 to 5 years or when cracks (longitudinal, transverse, corner) appear.
  • Use Falling Weight Deflectometer (FWD) or Ground Penetrating Radar (GPR) to detect voids beneath the pavement.

• Cause of Voids:

  • Permanent settlement/deformation of granular layers and subgrade under heavy axle loads.
  • Voids increase stresses causing cracking due to curling and temperature gradients.

• Filling Voids (Appendix I):

  • Use cementitious grouting to fill detected voids.
  • Grouting also used for retrofitting dowel bars/tie bars.

General Method for Cement Grouting (from Appendix I)

1. Drill holes at void locations identified by FWD/GPR.
2. Inject cement grout under pressure to fill voids.
3. Monitor grout volume and pressure to ensure complete filling.
4. Cure grout before opening pavement to traffic.

Important Specifications

Summary Diagram

flowchart TD
    A[Detection of Voids] -->|FWD/GPR| B[Locate Voids]
    B --> C[Drill Injection Holes]
    C --> D[Inject Cement Grout]
    D --> E[Void Filling & Compaction]
    E --> F[Pavement Rehabilitation]

Recommendation: Follow IRC 117 Section 8 and Appendix I strictly for detection and grouting procedures to extend pavement life and prevent cracking.

Load Transfer Efficiency (LTE) of Transverse Joints - IRC 117

Key Formula:

[ \boxed{ \text{LTE} = 100 \times \frac{D_2}{D_1} } ]

• (D_1): Deflection on the loaded side of the joint.
• (D_2): Deflection on the unloaded side of the joint.

If deflection sensors are spaced 300 mm apart, LTE can be adjusted as: [ \text{LTE} = 100 \times B \times \frac{D_2}{D_1} ] where (B) is a correction factor (typically 1 for 300 mm spacing).

Critical Conditions:

• Transverse joints: LTE < 50% indicates critical condition.
• Longitudinal joints: LTE < 40% indicates critical condition.
• Below these, retrofitting with dowel/tie bars as per IRC:SP:83 is recommended.

Measurement:

• Use Falling Weight Deflectometer (FWD) with sensors on both sides of the joint.
• Compare deflections under standard impact loads (e.g., 5500 kg, 7600 kg, 11000 kg).

Sample LTE Data (from CRRI on NH-2):

Notes:

• LTE close to 100% means excellent load transfer.
• LTE decreases with joint deterioration.
• Early detection of voids and joint deterioration via FWD is essential for maintenance.

flowchart LR
    A[FWD Load Applied] --> B[Measure Deflection D1 on Loaded Side]
    A --> C[Measure Deflection D2 on Unloaded Side]
    B & C --> D[Calculate LTE = 100 * (D2/D1)]
    D --> E{LTE < Critical Value?}
    E -- Yes --> F[Retrofit Joint (Dowel/Tie Bars)]

IRC 117: Frequency of Structural Evaluation Tests for Rigid Pavements

• Test Interval: Structural evaluation tests (e.g., Falling Weight Deflectometer - FWD) should be repeated every 3 to 5 years to monitor pavement health and enable timely maintenance.

• Load Transfer Efficiency (LTE):

  • LTE values between 1.05 and 1.15 are typical; adopt 1.05 as a conservative value.
  • Low LTE indicates need for retrofitting dowel bars and tie bars before severe deterioration.

• Testing Across Cracks: Tests must include sensors across cracks to check if cracks extend full depth and assess load transfer.

• Deflection Measurement Setup: Sensors spaced at 300 mm intervals at joints (see Fig.7 in IRC 117) for accurate deflection profiles.

• Data Recording: Use the format similar to CRRI’s NH-2 FWD test results (Appendix IV).

Summary Table: Frequency of Structural Evaluation

flowchart TD
    A[Start] --> B[Conduct FWD Test]
    B --> C{LTE Value}
    C -->|>=1.05| D[Monitor & Repeat in 3-5 years]
    C -->|<1.05| E[Retrofit dowel & tie bars]
    E --> D

This ensures proactive maintenance and prolongs pavement life as per IRC 117 guidelines.

Retrofitting of Dowel and Tie Bars (IRC 117 & IRC:SP:83-2008)

Key Specifications & Process:

• Crack Mapping: Essential before retrofitting; survey crack type, length, width, and condition.
• Load Transfer Efficiency (LTE): Measured by Falling Weight Deflectometer (FWD). LTE < 1.05–1.15 indicates need for retrofitting.
• Dowel/Tie Bar Retrofit: Refer to IRC:SP:83-2008 Chapter 11 for special techniques.

Important Formulas & Concepts:

1. Load Transfer Efficiency (LTE): [ LTE = \frac{\text{Unloaded Slab Deflection}}{\text{Loaded Slab Deflection}} \times 100% ]

   • Typical LTE values > 90% indicate good load transfer.
   • Tables from Appendix-IV show LTE ~ 97-99% for healthy joints.

2. Grouting Process for Voids (Clause 1.2):

   • Drill 12-15 mm dia holes at 1 m spacing.
   • Inject grout at 0.35 N/mm² pressure until voids are filled.
   • Use vacuum for air removal if needed.
   • Seal holes with epoxy mortar.

3. FWD Testing Parameters (Appendix-V):

   • Poisson’s ratio: Concrete = 0.15, Subgrade = 0.45
   • Calculate modulus of subgrade reaction (k), elastic modulus (E), and flexural strength (f_r) from deflection basin data.

Summary Table: LTE from FWD Testing (Example)

Mermaid Diagram: Retrofit Process Flow

flowchart TD
    A[Crack Mapping & Survey] --> B[FWD Testing & LTE Calculation]
    B --> C{LTE < 1.05

Fatigue Behaviour of Cement Concrete (IRC 117 referencing IRC 58-2011)

Key Formulas:

1. Fatigue Life (N) vs Stress Ratio (SR):

• For SR < 0.45,
  [ N = \text{unlimited} ]

• For 0.45 ≤ SR ≤ 0.55,
  [ N = 4.2577 \times SR^{-3.268} ]

Where,
[ SR = \frac{\text{Load Stress}}{\text{Modulus of Rupture of Concrete}} ]

2. Cumulative Fatigue Damage (CFD):

[ CFD = \sum_{i=1}^k \frac{n_i}{N_i} ]

• (n_i) = number of load repetitions in interval (i)
• (N_i) = fatigue life for stress ratio in interval (i)

Note: CFD for bottom-up cracking is significant between 10 AM - 4 PM (due to wheel load + positive temperature gradient). For top-down cracking, CFD is significant between 0 AM - 6 AM (temperature effects dominate).

Axle Load Spectrum (Table excerpt from IRC 58-2011):

Loads below these intervals contribute less to fatigue.

Traffic Growth Formula for Cumulative Axles:

[ C = 365 \times A \times \frac{(1 + r)^n - 1}{r} ]

• (C) = cumulative number of axles at evaluation time
• (A) = initial daily axles
• (r) = annual growth rate (decimal)
• (n) = years after construction

Practical Notes:

• Use modulus of rupture from FWD tests for accurate SR calculation.
• Sum of fatigue damage from bottom-up and top-down cracking must be **< 1

Grouting Process for Voids (IRC 117 - Clause 1.2)

Key Specifications:

• Hole diameter: 12–15 mm
• Hole spacing: 1 m square grid
• Injection pressure: 0.35 N/mm²
• Grout material: Cement-based or polymer-modified grout as per site conditions
• Curing: As per grout manufacturer recommendations or minimum 24-48 hours typical

Additional Notes:

• Void detection via FWD (Falling Weight Deflectometer) or GPR (Ground Penetrating Radar) is recommended before grouting.
• Retrofit of dowel/tie bars covered in IRC:SP:83-2008 (Chapter 11).

flowchart TD
    A[Drill Holes 12-15 mm dia @1m²] --> B[Blow Compressed Air]
    B --> C[Plug Holes & Clean Surface]
    C --> D[Inject Grout @ 0.35 N/mm²]
    D --> E{Grout Flow Stops or Flows Out Adjacent Hole?}
    E -- No --> D
    E -- Yes --> F[Roughen & Fill Holes with Epoxy Mortar]
    F --> G[Cure Grout]
    G --> H[Open Traffic]

This process ensures effective filling of voids under rigid pavements, restoring slab support and extending pavement life.

IRC 117: Pavement Condition Data Sheet - Key Points

1. Pavement Condition Data Sheet (Appendix II)

• Records crack types and sizes:
  • Transverse cracks < 1.5 m and > 1.5 m
  • Longitudinal full-depth cracks
  • Pavement edge pop-outs (mm)
  • Condition of joints
  • Roadside drain condition (NE/PF/F)
• Includes survey details: Section, Road Name, Date (Clause 6.1)

2. Falling Weight Deflectometer (FWD) Test (Appendix III & V)

• Used to determine:
  • Subgrade modulus (k, MPa/m)
  • Elastic modulus of concrete slab (E, MPa)
  • Flexural strength of concrete (MPa)
• Inputs:
  • Load (P, kN)
  • Radius of loading plate (a, mm)
  • Slab thickness (h, mm)
  • Deflections at 0, 300, 600, 900 mm from load center (mm)
  • Poisson’s ratio: Concrete (0.15), Subgrade (0.45)

3. Key Formulas & Parameters

• Radius of relative stiffness:
  [ l = \left(\frac{Eh^3}{12k(1-\mu^2)}\right)^{0.25} ]
• Modulus of Subgrade Reaction (k) and Elastic Modulus (E) are derived via iterative methods or Excel sheets based on deflection basin.
• Flexural strength ( f_r ) calculated from slab strength data.

4. Load Transfer Efficiency (LTE) (Appendix IV)

• LTE (%) = (\frac{\text{Deflection of Unloaded Slab}}{\text{Deflection of Loaded Slab}} \times 100)
• Typical LTE values from tests range 97% - 100%, indicating good joint condition.

Summary Table Example (FWD Test)

Key Formulas & Specifications for Subgrade and Concrete Properties (IRC 117):

1. Deflection Basin Area (A):
   [ A = 6 \times [D_0 + 2(D_1 + D_2 + D_3)]^2 ]
   Where:

• (D_0, D_1, D_2, D_3) = Deflections at 0, 300, 600, and 900 mm respectively (mm).

2. Radius of Relative Stiffness (l):
   Obtained from charts or Excel sheet based on deflection basin area and slab thickness (h).

3. Modulus of Subgrade Reaction (k):
   Calculated using normalized deflections (d_i) from charts/equations, average taken as (k) (MPa/m).
   Note: Use 50% of FWD-determined (k) for design.

4. Elastic Modulus of Concrete (Ec):
   [ E_c = 1000 \times \frac{h^3 \times k}{l^3 \times (1 - \mu_c^2)} ]
   Where:

• (h) = slab thickness (mm)
• (k) = subgrade modulus (MPa/m)
• (l) = radius of relative stiffness (mm)
• (\mu_c) = Poisson's ratio for concrete (typically 0.15)

5. Concrete Cube Strength (fck):
   [ f_{ck} = \left(\frac{E_c}{5000}\right)^{0.5} ]

6. Flexural Strength (fmr):
   [ f_{mr} = 0.7 \times f_{ck}^{0.5} ]

Example Summary (From Appendix III):