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How to use the Bituminous Mix Design Calculator

The Bituminous Mix Design Calculator follows the Marshall method: it blends the aggregates, works out specimen volumetrics (VA, VMA, VFB), estimates the optimum bitumen content (OBC), checks it against MoRTH-style limits and draws the design charts.

Open the Bituminous Mix Design Calculator ›

On this page
  1. Quick start
  2. Tab 1 — Setup
  3. Tab 2 — Specimens
  4. Tabs 3 & 4 — Results and report
  5. Questions people ask

Quick start

  1. In Setup choose the mix type, enter Gb and the aggregate blend, and press Calculate Blend.
  2. In Specimens add one row per bitumen content with Gmb, Gmm, stability and flow, and press Calculate All.
  3. Read OBC and the check in Results; print the sheet from Report.

Tab 1 — Setup

FieldWhat to enterTypical valueTip
Project / JobName of the work.
Mix TypeDBM, BC, SDBC, BM or Other.DBM / BC
Bitumen Gradee.g. VG-30.VG-30
Bitumen Specific Gravity (Gb)From the bitumen test.1.01 – 1.03
Nominal Max Aggregate Size9.5 – 37.5 mm.12.5 / 19 mm

Aggregate blend

Press + Add Aggregate for each fraction and enter its name, % in the blend and bulk specific gravity (Gsb). Percentages must add up to 100. Press Calculate Blend for the combined Gsb.

FieldWhat to enterTypical valueTip
Target Air Voids (%)Design air voids.4.0
Specimen height / diameter (mm)Optional — standard Marshall mould.63.5 / 101.6

Tab 2 — Specimens

One row per bitumen content (usually 5 contents at 0.5 % steps, each the average of 3 specimens). Press + Add Specimen, then Calculate All.

ColumnWhat to enterTypicalTip
Bitumen %Bitumen content by weight of mix.4.0 – 6.0 %
GmbBulk specific gravity of the compacted specimen.Enter directly, or fill the three weights and it is calculated.
Weight in air / SSD weight / water weight (g)From the bulk density test.
GmmMaximum theoretical specific gravity (Rice test).
Stability (kN)Marshall stability (corrected for height).≥ 9 kN (DBM/BC)
Flow (mm)Marshall flow.2 – 4 mm

Tabs 3 & 4 — Results and report

Results shows VA, VMA and VFB for each bitumen content, the Marshall results table, the estimated OBC (at the target air voids), the acceptance check at OBC and the charts (stability, air voids and flow against bitumen content). Report gives the final mix design sheet: Print / Save PDF, Save Project and Load Saved Project.

The limits shown are a MoRTH-style guide only. Always check against the exact specification and grading of your contract.

Questions people ask

How is the optimum bitumen content found?

At the target air voids (usually 4 %) from the air voids–bitumen content curve, then checked for stability, flow, VMA and VFB.

Do I need Gmm for every specimen?

Enter the Gmm for each bitumen content; it can be measured or back-calculated from the effective specific gravity of the aggregate.

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