Overlay Design for Rigid Pavements

Overlay Design for Rigid Pavements

Overlay Design for Rigid Pavements

Step 1: Pavement Condition Survey

Perform visual inspection and non-destructive testing to assess the condition of the pavement.

Step 2: Data Collection

Collect data such as historical construction details, traffic loads, and axle load surveys.

Step 3: Deflection Analysis Using Falling Weight Deflectometer (FWD)

Perform FWD tests at radial distances to collect deflection data for various points. The following formulas are used:

Area Parameter (A) of the Deflection Basin

\[ A = 6 \left( \frac{D_1}{D_0} + \frac{D_2}{D_0} + \frac{D_3}{D_0} \right) \]

Where:

  • A = Area parameter of the deflection basin
  • D_0 = Deflection at the center of the loading plate (0 mm from the center)
  • D_1 = Deflection at 300 mm from the center
  • D_2 = Deflection at 600 mm from the center
  • D_3 = Deflection at 900 mm from the center

Radius of Relative Stiffness (l)

The radius of relative stiffness (l) can be evaluated from charts in the guidelines.

Step 4: Evaluation of Pavement Distresses

Modulus of Subgrade Reaction (k-value)

\[ k_i = \frac{P \cdot l^2}{D_i} \]

Where:

  • k_i = Modulus of subgrade reaction (MPa/m)
  • P = Load applied (kN)
  • l = Radius of relative stiffness (mm)
  • D_i = Measured deflections at various radial distances

Elastic Modulus of Concrete (Ec)

\[ E_c = \frac{12 \cdot (1 - \mu_c^2) \cdot k \cdot l^3}{h^3} \]

Where:

  • E_c = Elastic modulus of concrete (MPa)
  • \mu_c = Poisson's ratio of concrete
  • k = Modulus of subgrade reaction (MPa/m)
  • l = Radius of relative stiffness (mm)
  • h = Thickness of concrete layer (mm)

Compressive Strength of Concrete (fc)

\[ f_c = \left( \frac{E_c}{5000} \right)^{0.5} \]

Flexural Strength of Concrete (fmr)

\[ f_{mr} = 0.7 \cdot (f_c)^{0.5} \]

Step 5: Calculation of Remaining Life (Fatigue Life)

To calculate the fatigue life, use the following equation from IRC:58-2011:

\[ N = 4.2577 \cdot 10^3 \cdot \left( \frac{1}{SR^{3.268}} \right) \quad \text{for} \ 0.45 \leq SR \leq 0.55 \]

or

\[ \log N = 0.9718 - 0.0828 \cdot SR \quad \text{for} \ SR > 0.55 \]

Cumulative Fatigue Damage (CFD)

\[ CFD = \sum \frac{n_i}{N_i} \]

Step 6: Design of Overlay

The overlay thickness is determined based on traffic loads, remaining life, and pavement distress calculations.

Step 7: Rehabilitation of Joints and Cracks

Filling of Voids

Voids are filled using cement grout.

Load Transfer Efficiency (LTE)

Load transfer efficiency at joints is calculated using the following formula:

\[ LTE = 100 \cdot \left( \frac{D_2}{D_1} \right) \]

Step 8: Final Overlay Placement

After repairs, the overlay is placed (either concrete or asphalt).

Step 9: Post-Construction Monitoring

Periodic monitoring of the overlay is essential.

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