Tests on bituminous binders

Bituminous binders are tested to check that they have the right consistency, safety, purity and durability for the climate and the traffic. The tests are given in IS:73 / IS:1201-1220 and adopted in NRS 2070 and IRC:SP:53.

Consistency tests (main)

1. Penetration test - depth in units of 0.1 mm to which a standard needle (100 g, 5 s, 25 degrees C) penetrates; it classifies the grade (30/40, 60/70, 80/100).
2. Softening point test (ring and ball) - temperature at which bitumen softens; shows the temperature susceptibility.
3. Ductility test - distance in cm to which a briquette of bitumen can be stretched (27 degrees C in IS:1208, 25 degrees C in ASTM; 50 mm/min) before breaking; shows cohesion and flexibility.
4. Viscosity test - flow time in seconds (Saybolt, orifice/tar viscometer) or absolute and kinematic viscosity; gives the grade (VG-10, 20, 30, 40) and the mixing and compaction temperatures.

Other tests

5. Flash and fire point - safe heating temperature.
6. Specific gravity (about 0.97-1.02) - for mix calculations.
7. Loss on heating (thin-film oven/RTFOT) - ageing and volatile loss.
8. Solubility in trichloroethylene - purity (at least 99%).
9. Float test - consistency of tars, cutbacks and thick liquid binders.
10. Water content, Fraass breaking point, elastic recovery (modified binders), and adhesion/stripping with aggregates.

Why needed

Penetration and viscosity indicate stiffness at service/mixing temperatures, softening point shows high-temperature behaviour, ductility shows cracking resistance, flash point gives safety, and solubility and loss on heating show quality.