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Austroads Rigid Pavement Design: Concrete Base Thickness, Joints & Reinforcement

Step 1: pick the heavy vehicles and their axle group loads → design traffic in heavy vehicle axle groups (HVAG). Step 2: subgrade, subbase, concrete and reliability → base thickness from flexural fatigue and erosion (PCP, JRCP, CRCP, SFCP). Step 3: dowels, tie bars and reinforcement.

Version: 2026-10-29 09:40Reference: Austroads AGPT02-26, Chapters 7, 9 & 10 and Section 12.9Author: Shahid Pervaiz
👋 You are looking at sample data so you can see what this tool does. Change any value, or click New Project to start your own.

Project

Axle loads & design traffic

Traffic growth and design lane

How do you want to describe the heavy traffic?

Add one row per vehicle type (and load state, e.g. laden and empty as two rows). Enter the two-way daily number of that vehicle in the opening year and the load on each axle group. The axle groups start with the typical layout of each Austroads class (Figure 7.1) at the Standard Load — change them to your survey or legal loads. Light vehicles (classes 1–2) are ignored by the method (Section 7.2).

#Vehicle (Austroads class) & descriptionTwo-way per dayAxle groups & loadsGroupsESA / vehicle (damage factor)ESA / day (two-way)
Legal axle load limits:
Axle group codes (Austroads Section 7.2, Tables 7.7–7.8)
CodeAxle groupTypical useStandard load = 1 ESA
SASTSingle axle, single tyres (2 tyres)Steering (front) axle of most trucks and buses53 kN (5.4 t)
SADTSingle axle, dual tyres (4 tyres)Rear axle of a 2-axle truck; the Austroads Standard Axle80 kN (8.2 t)
TASTTandem axle, single tyres (2 axles, 4 tyres)Twin-steer front of 4-axle rigid trucks89 kN (9.1 t)
TADTTandem axle, dual tyres (2 axles, 8 tyres)Rear of 3-axle rigid trucks (10-wheeler); drive axles of prime movers135 kN (13.8 t)
TRSTTriaxle, single tyres (3 axles, 6 tyres)Trailers on wide single (super single) tyres121 kN (12.3 t)
TRDTTriaxle (tridem), dual tyres (3 axles, 12 tyres)Semi-trailer rear group (18- and 22-wheelers)182 kN (18.6 t)
QASTQuad-axle, single tyres (4 axles, 8 tyres)Heavy trailers on wide single tyres150 kN (15.3 t)
QADTQuad-axle, dual tyres (4 axles, 16 tyres)Heavy-haulage and some low-loader trailers226 kN (23.0 t)

Single-tyre groups: the standard load above is for tyres narrower than 375 mm. Wider tyres carry more for the same damage (Table 7.8), so pick the tyre width in the list next to the code. ESA of a group = (load ÷ standard load)4 (flexible pavements; information only here). Axles less than 2.1 m apart count as one group.
Rigid design: each group load is multiplied by the load safety factor and checked for fatigue (F1 = 9 SAST, 18 SADT and TAST, 36 TADT, 54 TRDT, 72 QADT) and erosion (F4, QADT 54). TRST and QAST are not covered by Equations 58 and 61.

Legal limits are the most a truck may carry, not what it does carry. Overloading is common, so use axle load survey data where you have it. The Pakistan truck types in the vehicle list start at the NHA limits.

Use this when you only have a traffic count: the axle groups are spread over loads with the Austroads example distribution (Appendix F). The result is a demonstration (QUALIFIED) — rigid pavements are very sensitive to the real axle loads.

Capacity check (Section 7.4.6)

Concrete base thickness: fatigue and erosion (Section 9.4)

Pavement type and support

Layered subgrade within 1 m: equivalent design CBR (Equation 57)

List the layers below the subbase, top first, down to 1.0 m. Layers under 200 mm are combined with the next one (lower CBR); a weaker layer over a stronger one is not allowed; the result is limited to 15%.

#Thickness (m)CBR (%)

Concrete and reliability

Roundabout

Joints, dowels, tie bars & reinforcement (Sections 9.4.6–9.7)

Compare base types: cost and whole-of-life cost (Sections 2.2.7, 9.2.1, Chapter 10)

Base types: PCP = plain (jointed unreinforced) concrete pavement, no steel mesh; JRCP = jointed reinforced concrete pavement (longer slabs with steel mesh); CRCP = continuously reinforced concrete pavement (no contraction joints, continuous longitudinal steel); SFCP = steel fibre reinforced concrete pavement (fibres mixed into the concrete). Dowelled = steel dowel bars across the transverse joints transfer load between slabs; undowelled = no dowels, load passes by aggregate interlock.

Base types to consider
Untick types that do not suit the project; they are then listed as not considered.

Rates (your prices, in place)

Whole-of-life cost (Equation 67)

Base typePeriodic maintenance per kmEvery (years)
PCP undowelled
Plain concrete pavement, no dowels at the joints
PCP dowelled
Plain concrete pavement, dowels at the joints
JRCP
Jointed reinforced concrete pavement
CRCP
Continuously reinforced concrete pavement
SFCP
Steel fibre reinforced concrete pavement

Your estimates of joint resealing, slab and crack repairs per km at each treatment (0 allowed); Austroads gives no quantities (Section 10.4).

Method, assumptions & references

  • Design traffic (Sections 7.4, 7.7, H.3): cumulative heavy vehicle axle groups NDT,HVAG = NDT × NHVAG (Equations 30–35), split by axle group type and load (traffic load distribution, Section 7.5). In the vehicle mix every axle group of every vehicle is one load; the AADT route uses the Austroads example distribution (Appendix F).
  • Fatigue (Equations 58–59): Sr = Se/(0.944 fcf) × (P · LSF / 4.45F1)0.94; log Nf = (0.9719 − Sr)/0.0828 for Sr > 0.55; Nf = (4.258/(Sr − 0.4325))3.268 for 0.45 ≤ Sr ≤ 0.55; unlimited below 0.45. F1 = 9 SAST, 18 SADT and TAST, 36 TADT, 54 TRDT, 72 QADT.
  • Erosion (Equation 61): log(F2Ne) = 14.524 − 6.777 [max(0, (P · LSF / 4.45F4)2 · 10F3/41.35 − 9.0)]0.103; F2 = 0.06 without and 0.94 with a concrete shoulder; F4 as F1 but 54 for QADT.
  • Equivalent stress Se and erosion factor F3 (Equation 60) from the base thickness D and the effective subgrade CBR Ef, with the coefficients of Table 9.4 (stress) and Tables 9.5 / 9.6 (erosion, undowelled / dowelled or CRCP).
  • Design thickness (Table 9.3, Section 9.4.1): the least thickness with total fatigue ≤ 100% and total erosion ≤ 100%, rounded up to 5 mm, not less than the minimum of Table 9.7 (125 mm below 106 HVAG, Section 12.9.4). Repetitions with allowable loads above 1011 are not counted (Table 9.3 step 13).
  • Effective subgrade strength (Figure 9.1): the four subbase lines are straight on the log–log chart and are fitted to it (CBRE = a × CBRk, maximum 75%); below CBR 2% use 150 mm LCS and 5%. Layered subgrade: Equation 57.
  • Light traffic (below 106 HVAG, Section 12.9): erosion is not normally a distress mode, so only fatigue governs; erosion is still shown.
  • Joints and reinforcement: dowels Table 9.9 (Grade 250N, 450 mm, 300 mm centres); tie bars and JRCP / CRCP transverse steel by subgrade drag, As = μLρgD/(1000fs) (Equation 62); CRCP longitudinal steel Equations 63–65 (minimum 0.67%) and crack spacing Equation 66.
  • Verified against the worked example of Appendix M (PCP with shoulders, 150 mm LCS, 4 × 107 HVAG, LSF 1.3): equivalent stresses, erosion factors and allowable repetitions match the printed tables, and the design is 215 mm.
  • Source: Austroads (2026) Guide to Pavement Technology Part 2: Pavement Structural Design, AGPT02-26 (Edition 5.2), Chapters 7, 9 and 12, Appendices F, H and M. This free tool is independent and not endorsed by Austroads; check designs against the guide and your road agency’s requirements.

How to use the Austroads Rigid Pavement Design tool

The tool designs the concrete base of a rigid pavement to the Austroads Guide (AGPT02-26, Chapter 9 and Section 12.9): traffic first, then the base thickness from fatigue and erosion, then joints and reinforcement. The calculations run in your browser; your design inputs are not uploaded (the site only counts page visits anonymously).

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Start with the sample. The page opens with sample data so you can see what the tool does. Load Sample Data brings it back; New Project clears it. Hover over any box for a short explanation.
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Step 1 — traffic. Enter the design period, growth, direction factor and lane distribution factor, then describe the heavy traffic:
  • Vehicle mix & axle loads (recommended): + Add vehicle, pick an Austroads class or a Pakistan NHA truck type, enter how many pass per day (both directions) and the load on each axle group. Every axle group of every vehicle becomes one load in the design. Enter laden and empty trucks as separate rows. TRST and QAST groups are not covered by the rigid method.
  • AADT, %HV and NHVAG: uses the Austroads example load distribution (Appendix F); the result is marked QUALIFIED (demonstration), because rigid pavements are very sensitive to the actual axle loads.
The result is the design traffic NDT,HVAG in heavy vehicle axle groups. ESA in the vehicle table is for flexible pavements and is shown for information only.
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Step 2 — base thickness. Choose the base type (PCP undowelled or dowelled, JRCP, CRCP or SFCP) and whether there is a concrete shoulder (integral, structural, tied, or a substantial tied kerb — Section 9.3.5). Enter the subgrade design CBR (for a layered subgrade open Equation 57), choose the subbase (Table 9.1 minimum for your traffic) — the effective subgrade CBR comes from Figure 9.1 — and enter the concrete flexural strength and reliability (load safety factor, Table 9.2). Tick Roundabout where it applies.
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Reading the result. The tool finds the least thickness with total fatigue ≤ 100% and total erosion ≤ 100%, rounds it up to 5 mm and applies the minimum of Table 9.7 (125 mm below 106 HVAG). The chart shows damage against thickness; the tables (as Appendix M) give each axle group load, its allowable repetitions and damage. Add any construction allowance in Additional thickness. Type a Trial base thickness to check your own value. Below 106 HVAG only fatigue governs (Section 12.9). QUALIFIED means the numbers work but an input is outside what the method covers (example load distribution, subbase below Table 9.1, concrete below the minimum strength, traffic below 103 HVAG) — it is not a design approval.
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Step 3 — joints and reinforcement. Pick the friction coefficient (Table 9.10) and the relief distances. You get the joint spacing guidance, dowel size (Table 9.9), tie bar spacing (Equation 62, indicative), JRCP mesh area, and for CRCP the longitudinal steel (Equations 63–65, minimum 0.67%), bar spacing, crack spacing (Equation 66) and transverse steel.
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Step 4 — compare base types. Every base type (PCP undowelled and dowelled, JRCP, CRCP, SFCP) is designed with your Step 2 inputs. Enter the rates for concrete, steel fibre concrete, subbase and steel, the width and, for the whole-of-life cost (Equation 67), the analysis period, discount rate, optional routine maintenance and salvage value, and your periodic maintenance per base type. The types are ranked by whole-of-life cost (or construction cost, or thickness until the inputs are complete); qualified designs are never ranked first. Untick types in Base types to consider; Use loads a type into Step 2. The box Choosing between the base types lists the Austroads Chapter 10 criteria.
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Vehicles from a spreadsheet. Export Vehicles (.csv) shows the format; edit it and use Import Vehicles (.csv). Columns: Class, Description, PerDay (two-way), AxleGroups (e.g. SAST 53; TADT 135; TRDT 182, loads in kN).
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Save, print, report. Save Project (.json) and Load Project keep your inputs; autosave remembers the last inputs in this browser. Generate Report builds a report with report information (guide edition, tool build, input checksum, traffic source, time, review status), traffic, the thickness design with all its messages and damage tables, joints and reinforcement, and the scope and limitations.
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Thicknesses are minimum design values without construction tolerance. Check results against AGPT02 and your road agency’s requirements before use.

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