Bitumen 60/70 and PMB for Road Projects: Grades, Testing, Logistics

Bitumen is a refinery residue sold as an engineering material. Road contractors specify it by a grade, the refinery produces it to a standard, and between the two sit tests, temperatures and a logistics chain that is harder than for any other liquid commodity because the product is solid at ambient temperature. This article covers the paving grades that dominate EPC road projects, the polymer-modified binders used for heavy traffic, and the practical points of buying and shipping them.

Penetration grades

Paving bitumen is classified by penetration: the depth, in tenths of a millimetre, that a standard needle sinks into the sample at 25 °C under 100 g for 5 seconds (EN 1426, ASTM D5). Lower numbers mean harder binder. Two naming systems coexist:

• EN 12591, the European standard, defines grades such as 20/30, 35/50, 50/70, 70/100 and 160/220. Each grade carries requirements for softening point, flash point, solubility, resistance to hardening (RTFOT) and optional properties such as kinematic viscosity and Fraass breaking point.
• ASTM D946 and the national standards derived from it define 40/50, 60/70, 85/100, 120/150 and 200/300. The 60/70 grade is the workhorse of road projects in the Middle East, South and Southeast Asia and much of Africa.

India uses viscosity grades (VG-10 to VG-40 under IS 73) and North America performance grades (PG 64-22 and similar). A tender in one system and an offer in another need a documented equivalence, agreed by the engineer, before any cargo is fixed.

Specification of 60/70 and 50/70

The RTFOT lines (rolling thin film oven test) simulate ageing during hot mixing and show whether the binder still performs after the asphalt plant. A certificate without RTFOT results is incomplete.

Polymer-modified bitumen

For heavy traffic, high ambient temperatures or thin surface courses, the road design often calls for polymer-modified bitumen (PMB), typically modified with SBS (styrene-butadiene-styrene). EN 14023 designates PMB by penetration range and minimum softening point, for example PMB 45/80-65: penetration 45 to 80 dmm, softening point at least 65 °C. Additional requirements include elastic recovery at 25 °C (EN 13398), cohesion by force ductility (EN 13589), storage stability as the difference in softening point between top and bottom of a stored sample (EN 13399) and Fraass breaking point for cold climates (EN 12593).

PMB is produced at a modification plant, not at the refinery, must be kept agitated at the specified temperature and has a limited storage life before separation. It is therefore produced close to the project or at the asphalt plant from base bitumen and polymer.

Rule: bitumen is bought against a penetration grade and a named standard, inspected at loading on a representative sample, and shipped with a temperature log. A certificate without RTFOT results, a grade without a standard or a cargo without a temperature history is not deliverable to a road project.

Packing and transport

Bulk

Bitumen tankers load at 150 to 170 °C and maintain the cargo with heating coils. Bulk is the lowest-cost route for parcels of several thousand tonnes to ports with heated storage; the buyer needs insulated receiving tanks or heated road tankers to lift from the vessel within the laytime.

Drums

New steel drums of about 180 kg net (nominal 200 litre) are the standard for destinations without heated storage. Advantages: any port, any truck, storage for months. Disadvantages: the drum is cut open and the bitumen melted at the plant, drum disposal, and the risk of underfilled or recycled drums. A specification should state new drums, net weight per drum, pallet or loose stowage and a drum count verified by the inspector. A 20-foot container holds around 80 drums.

Bitutainers and jumbo bags

Insulated, heated tank containers allow multimodal bulk delivery of 20 to 24 tonnes per unit. Jumbo bags with a meltable liner (300 to 1,000 kg) are cheaper than drums but require a suitable melting unit at the plant.

Inspection and documents

1. Sampling at loading by an independent inspector (SGS, Intertek, Bureau Veritas) according to EN 58 or ASTM D140, from bulk tanks or a statistical selection of drums.
2. Certificate of quality listing all parameters of the agreed standard, including RTFOT, with test methods.
3. Certificate of quantity: weight by shore tank or flow meter for bulk, drum count and average net weight for packed cargo.
4. Certificate of origin, bill of lading, packing list and, for drums, a container stuffing report.
5. Temperature log from loading to discharge for bulk cargo.

Bitumen cannot be returned. A grade mistake, an oxidised cargo or underweight drums become a problem on the project schedule. Specify precisely, inspect at origin and plan the heating chain before fixing the vessel.