Project Information

Aggregate Properties

ASTM C127/C128
Calculated from absorption and bulk specific gravity
ASTM D70
ASTM C127/C128
Enter sieve sizes and passing percentages

Trial Mixes Data

Trial # Bitumen Content (%) Gmm Gmb Stability (kN) Flow (mm) Actions

Results & Graphs

Bitumen Content (%) Stability (kN) Flow (mm) Air Voids (Va) (%) VMA (%) VFB (%)

Optimum Bitumen Content (OBC) Determination

Optimum Bitumen Content (OBC)
-
% by weight of mix
Stability at OBC
-
kN
Flow at OBC
-
mm
Air Voids at OBC
-
%
VMA at OBC
-
%
VFB at OBC
-
%

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Interactive Guide

  1. Select aggregate gradation based on project requirements
  2. Determine specific gravities of aggregates and bitumen
  3. Prepare trial mixes with varying bitumen content (typically 3.5% to 6.5% in 0.5% increments)
  4. Compact specimens using Marshall hammer (75 blows per side)
  5. Determine bulk specific gravity (Gmb) of compacted specimens
  6. Determine theoretical maximum specific gravity (Gmm) for each bitumen content
  7. Test specimens for Marshall Stability and Flow at 60°C
  8. Calculate air voids (Va), VMA, and VFB for each mix
  9. Plot graphs and determine optimum bitumen content (OBC)
  10. Verify OBC meets all specification requirements

Parameter BC (IRC:SP:53) DBM (IRC:SP:53) ASTM D1559
Stability (kN) Min 9 Min 8 Min 8.9
Flow (mm) 2-4 2-4 2-4
Air Voids (%) 3-5 3-5 3-5
VMA (%) Min 14 Min 13 Varies
VFB (%) 65-75 65-78 65-75

Air Voids (Va)
Va = (Gmm - Gmb)/Gmm × 100
Voids in Mineral Aggregate (VMA)
VMA = (1 - Gmb/Gsb) × 100
Voids Filled with Bitumen (VFB)
VFB = (VMA - Va)/VMA × 100