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Rigid Pavement Design Calculator

Rigid Pavement Design: ESAL and Slab Thickness - AASHTO 1993

Part 1 works out the design ESALs from the truck fleet and axle loads; Part 2 designs the concrete slab thickness with the AASHTO 1993 rigid-pavement equation. One full design report covers both.

by Shahid Pervaiz: pervaiz.shahid@gmail.com

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

Part 1 — Design ESALs (AASHTO 1993 Appendix D; the slab thickness D and p_t here are temporary assumptions for the load equivalency factors)

§1 · Design Parameters

Slab Thickness D (in)

Terminal Serviceability p_t

Annual Growth Rate g (%)

% / year

Traffic Count Year

Construction Completion

Design Life (years)

years after opening

Pre-construction (years)

Growth to opening (1+g)^p

count year → opening

Growth Factor GF (design life)

Direction distribution factor DDF

Lane distribution factor LDF

Design lane factor DDF × LDF

§2 · Truck Fleet — Expandable

Add one row per truck type. Each truck can have multiple axle groups (single, tandem, triple). LEFs are interpolated live from AASHTO Tables D.10–D.18. Each truck's Adopted Factor starts synced to its computed Composite LEF; setting it higher implies truck loading and/or tyre pressure above the adopted standard/reference conditions.

§3 · Annual ESAL Summary (Year of Traffic Count)

Note: setting an Adopted value higher than the computed composite LEF implies truck loading and/or tyre pressure above the adopted standard/reference conditions.

Truck Type		Front Axle	Mid. Axle	Rear1 Axle	Rear2 Axle	Total	Adopted	AADT	Daily ESAL
Total Daily ESAL									—
Total Annual ESAL									—
Growth to opening year (1+g)^p									—
Growth Factor over the design life, GF									—
Design lane factor DDF × LDF									—
Design-lane ESALs over the design life, millions									—

§4 · Design ESALs

Design life (from opening)

—

Growth Factor GF

—

Annual ESALs (base year)

—

Cumulative Design ESALs (design lane)

—

The cumulative design ESALs go straight into W₁₈ of Part 2, with the traffic years and the truck breakdown for the full report.

§5 · Year-by-Year Accumulation

Year	Calendar	Annual ESALs	Cumulative, design lane from opening

§6 · LEF Quick Reference (D & p_t above)

Part 2 — Slab thickness design (AASHTO 1993 rigid pavement equation; p_i, p_t and ΔPSI are set here)

A Project Data

Traffic count year

Construction completion year

Projected design year

Design life (yr)

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

Measured elastic modulus Ec (psi)Use a tested, project-specific value when available.

Elastic modulus of concrete Ec (psi)

Measured flexural strength Sc (psi)Use a tested, project-specific value when available.

Modulus of rupture Sc (psi)

Subgrade k = M_R / 19.4 (pci)

Subbase type for loss of support (Table 2.7)

Loss of support LS

Composite k∞ from Figure 3.3 (pci, optional)

Roadbed modulus M_R = 2555·CBR^0.64 (psi)

Measured effective k (pci)Plate-bearing or back-calculated value, before the loss of support correction.

Design k corrected for LS, Figure 3.6 (pci)

Ec = 57,000√f'c · Sc ≈ 7.5√f'c (estimate; use measured strength when available) · M_R = 2555·CBR^0.64 (as the flexible tool) · k = M_R/19.4 without subbase (AASHTO 1993 Part II 3.2.1) · composite k∞ from Figure 3.3 · loss of support: Table 2.7 and Figure 3.6 · assumed: bedrock deeper than 10 ft (no Figure 3.4 correction) and one season (no Figure 3.5 averaging) — otherwise enter the measured effective k

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 from AASHTO 1993 Table 2.6 — hover the J box for the values by shoulder type and joint load transfer

E Design Slab Thickness (D)

Design D (trial, cm)

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 (≥ 15 cm) sit on its true increasing branch. (Trial D is entered in cm and converted to inches internally, since the AASHTO 1993 equation is calibrated in inches.)

F Provided Pavement Structure

Provided D (cm)

Lean concrete thickness (cm)

Granular subbase thickness (cm)

Subbase / lean-concrete thicknesses are shown in the cross-section and report; for subbase credit in the k-value read the composite k∞ from AASHTO Figure 3.3 for this subbase (Section C).

✓ Slab Thickness Check

Provided D (cm, section F)

Design D (cm, section E)

Provided vs design D

Required D (cm)

—

Provided D (cm)

—

Status

—

Composite subgrade support buildup

Subgrade reaction, k_sg

—

Composite k∞ (Fig. 3.3 / M_R÷19.4)

—

Loss of support, LS

—

= Design k, Fig. 3.6 (pci)

—

Concrete properties

Elastic modulus, Ec (psi)

—

Modulus of rupture, Sc (psi)

—

G Pavement Cross-Section — schematic, not to scale below subgrade line

Not saved to a file yet 📅 Date format ↑ Part 1: ESALs

Method & practical use

Understand the result.

Evaluate the AASHTO 1993 concrete-pavement equation and compare trial and required slab thickness.

How to use this tool

Select the geometry or design case and confirm the displayed units.
Replace sample inputs with the project values, then calculate or review the live result.
Check the method, assumptions and output; save or print the calculation with its input record.

Units & method

Slab depth displayed in cm, converted to inches internally; Sc and Ec in psi; k in pci; traffic in millions of ESALs.

The 1993 empirical equation is solved on its physically relevant branch. Enter project-specific flexural strength and effective foundation k where available. The optional CBR and layer-factor estimates are simplified assumptions, not the full AASHTO seasonal support procedure.

FHWA NHI-05-037, Appendix C (May 2006): AASHTO 1993 equations ↗

Worked examples

Illustrative inputs for checking the method; these are not project records.

8-inch slab equation check

Use ZR = −1.282, S0 = 0.35, ΔPSI = 2.0, pt = 2.5, Sc = 690 psi, Ec = 4,000,000 psi, k = 100 pci, J = 3.2 and Cd = 1.0. D = 8 in (20.32 cm) gives log₁₀W18 = 6.421672, or 2.640413 million ESALs.

10-inch slab equation check

Use ZR = −1.282, S0 = 0.35, ΔPSI = 2.0, pt = 2.5, Sc = 690 psi, Ec = 4,000,000 psi, k = 100 pci, J = 3.2 and Cd = 1.0. D = 10 in (25.40 cm) gives log₁₀W18 = 7.031208, or 10.745030 million ESALs.

Frequently asked questions

What does this tool calculate or track?

Evaluate the AASHTO 1993 concrete-pavement equation and compare trial and required slab thickness.

Which units and assumptions should I use?

Slab depth displayed in cm, converted to inches internally; Sc and Ec in psi; k in pci; traffic in millions of ESALs. The 1993 empirical equation is solved on its physically relevant branch. Enter project-specific flexural strength and effective foundation k where available. The optional CBR and layer-factor estimates are simplified assumptions, not the full AASHTO seasonal support procedure.

Can I save or share the result?

Use the save, export and print controls shown in this workspace. Where CSV export is available, the exported data can be opened in a spreadsheet. Browser print can save a PDF.

How to use the Rigid Pavement Design Calculator (AASHTO 1993)

Everything runs in your browser — nothing is uploaded. If you are new to the tool, follow these steps in order.

Enter your inputs and read the results

Work down the worksheet from section A. Results update as you type, so there is no Compute button to press.

A Project Data and B Design Data — traffic and design years, reliability, standard deviation and serviceability.
C Concrete & Composite Subgrade Support — concrete strength and modulus, subbase and subgrade support k.
D Traffic Input and E Design Slab Thickness — design ESAL, load transfer and drainage coefficients, and the slab thickness D required.
F Provided Pavement Structure and G Cross-Section — the slab and layers you adopt, checked against the requirement, with a schematic cross-section.

When you open the tool it already holds sample values, and a yellow bar says You are looking at sample data. The bar goes away as soon as you type your own values or load a saved project.

Bring in the ESAL from the ESAL Calculator

The design ESAL W₁₈ of Part 2 comes straight from Part 1 (cumulative design ESALs) and updates as you change the trucks or traffic data; the traffic years and the truck breakdown go into the full report. ↑ Part 1: ESALs goes back to the truck fleet.
Save Project keeps the imported ESAL data with the project, so the report still has it when you open the project again.

See how the data file looks

Press Export Inputs (.csv). It downloads every input on the worksheet as a CSV file that opens in Excel, one row per input:

Column	What to enter	Example
Field ID	The input's code — don't change it	`reliability`
Parameter	Name of the input, for reference	`Reliability level`
Value	The value to use	`90`

Enter your own data and import it

Change the values in the Value column and save the file as CSV. Then press Import Inputs (.csv) and choose the file.

Rows are matched by Field ID; rows with an unknown ID are skipped.
Only the inputs listed in the file are changed.

Save your project and open it later

Save Project (.json) saves every input on the worksheet in one .json project file. Load Project opens that file again, on any computer.

The note beside the Save button tells you whether you have unsaved changes or when you last saved. If you try to close or leave the page with unsaved changes, the browser asks you to confirm first.

Use the project file for backups and for sharing with colleagues. Don't edit it by hand.

This tool does not autosave. Save your project before closing the page.

Print, PDF and report

Save One Page Design Report in PDF prints the worksheet as a one-page design summary. To get a PDF, choose Save as PDF as the printer in the print dialog.
Generate Full Design Report in PDF opens a form for the report's cover and narrative: project, client, consultant, date, background text and optional uploads (cover page, location plan, typical cross section and soil investigation report). Every field has a default, so you can press Generate Report straight away. The report opens in a new tab with its own Print / Save as PDF button; allow pop-ups if nothing opens.

Choose the date format

Press 📅 Date format in the toolbar and choose how dates are shown and typed in every date box: DD/MM/YYYY, MM/DD/YYYY, YYYY-MM-DD, DD-MM-YYYY, DD.MM.YYYY or DD-Mon-YYYY. Type a date in that format, or click the 📅 in a date box to pick it from a calendar. A date that doesn't fit the format is outlined in red and not accepted.

The same format is used in the printout and in the generated report and its PDF. It changes only how dates look — your saved project and CSV files are not affected. Your choice is remembered in this browser for every tool on this site.

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