Rigid Pavement Design Calculator

Roads — Slab Thickness Design Worksheet

by Shahid Pervaiz · pervaiz.shahid@gmail.com

METHOD AASHTO Guide for Design of
Pavement Structures, 1993
EQUATION Rigid Pavement — Empirical Slab Thickness Model

A Project Data

Construction completion year

Projected design year

Design life (yr)

Base year ADT (veh/day)

B Design Data

Standard axle load (kips)

Reliability level R (%)

Std. normal deviate Z_R

Overall standard deviation S₀

Initial serviceability P₀

Terminal serviceability Pₜ

Serviceability loss ΔPSI

Soaked CBR of subgrade (%)

Drainage coefficient C_d

Concrete strength f'c (psi)

C Concrete & Composite Subgrade Support

Elastic modulus of concrete Ec (psi)

Modulus of rupture Sc (psi)

Subgrade reaction k_sg (pci)

Subbase multiplier f_sb

Lean concrete multiplier f_lean

Composite k k_comp = k_sg·f_sb·f_lean (pci)

Ec = 57,000√f'c · Sc = 7.5√f'c (adopt 700 psi minimum) · k_sg = 20×CBR when CBR > 10%

D Traffic Input for Slab Design

Design ESAL, W₁₈ (million)

Joint load-transfer coeff. J

log₁₀(W₁₈) — left side

left side = log₁₀(W₁₈ × 10⁶) · J is restricted to 3.6–4.2 (doweled joints w/ AC shoulder)

E Design Slab Thickness (D)

Design D (trial, in)

Right side of equation, using Design D

Left side vs. right side

Enter a trial slab thickness and adjust it until the right side matches the left side (log₁₀W₁₈) — this is the Design D checked against the thickness provided below. Note: the equation has a mathematical singularity at small D; realistic slabs (≥ 6 in) sit on its true increasing branch.

F Provided Pavement Structure

Provided D (in)

Lean concrete thickness (cm)

Granular subbase thickness (cm)

Subbase / lean-concrete thicknesses are the reference values behind the f_sb / f_lean multipliers in Section C — edit them here to match what's actually being built.

Required D

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Provided D

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Status

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Composite subgrade support buildup

Subgrade reaction, k_sg

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× Subbase multiplier, f_sb

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× Lean concrete multiplier, f_lean

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= Composite k, k_comp (pci)

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Concrete properties

Elastic modulus, Ec (psi)

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Modulus of rupture, Sc (psi)

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