The binder is the cheapest part of the pavement and the reason it fails.

The reference system across Europe, Africa, the Middle East and much of Asia. Grades are named for the penetration range of a standard needle at 25 °C, in tenths of a millimetre — a lower number is a harder binder.

Two families are in common use and they are not interchangeable. EN 12591 designates grades as a range — 20/30, 30/45, 35/50, 40/60, 50/70, 70/100, 100/150, 160/220, 250/330 — and requires softening point, flash point, solubility, resistance to hardening after RTFOT and, for the softer grades, Fraass breaking point. ASTM D946/D946M covers 40–50, 60–70, 85–100, 120–150 and 200–300, with ductility, flash point, solubility and penetration on residue.

Grading by absolute viscosity at 60 °C — the temperature a pavement actually reaches in service — rather than by needle penetration at 25 °C. The Indian standard IS 73 is the dominant framework and has largely replaced penetration grading on Indian subcontinent tenders; ASTM D3381 covers the equivalent AC grades.

The advantage is that a viscosity grade constrains the binder at service temperature and after short-term ageing, which penetration alone does not. Where a tender cites VG, we quote VG and report the viscosity, not a penetration equivalent.

The Superpave system, specified under AASHTO M320 and ASTM D6373. A PG 64-22 binder is required to perform at an average seven-day maximum pavement temperature of 64 °C and down to a minimum pavement design temperature of −22 °C. The numbers are pavement temperatures, not air temperatures, and not a product recipe.

The same tests are run for every grade; only the test temperatures change. Binder is assessed unaged, after RTFO short-term ageing, and after PAV long-term ageing — dynamic shear rheometry for rutting and fatigue, bending beam rheometry for thermal cracking, rotational viscosity for pumpability. Where a specifier has moved to AASHTO M332 and MSCR grading for traffic level, we quote to that instead.

Base bitumen modified with elastomeric or plastomeric polymer — most commonly SBS — to widen the service temperature range, raise elastic recovery and resist permanent deformation under repeated heavy loading. Specified in Europe under the EN 14023 framework, and in India under IS 15462.

EN 14023 designations carry the penetration range and the minimum softening point: a PMB 45/80-65 is a 45–80 penetration binder with a softening point of at least 65 °C. Elastic recovery and storage stability are the parameters that separate a properly modified binder from a hot-blended one that will separate in the tank, so both are reported.

Bitumen modified with crumb rubber recovered from end-of-life tyres, giving much of the performance benefit of a polymer modified binder while consuming a waste stream. CRMB 50, 55 and 60 are the standard grades, the number denoting the minimum softening point in degrees Celsius.

Two production routes exist and they behave differently in the tank: the wet process, in which rubber is digested into the binder before delivery, and terminal blends, which are formulated for stability in storage. We state which route a parcel came from, because the handling and reheating regime is not the same.

Both reduce viscosity so the binder can be applied without heating to hot-mix temperature. Cutbacks dilute bitumen with a petroleum solvent and are classified by curing speed — rapid, medium and slow curing — under EN 15322 and the ASTM RC / MC / SC designations. Emulsions disperse bitumen in water with an emulsifier and carry no solvent, which is why most authorities now prefer them.

Cationic emulsions are specified under EN 13808, whose designation encodes the chemistry directly: in C60B4, C is cationic, 60 is the binder content in percent, B is bitumen, and 4 is the breaking class. A P in the code indicates polymer modification, an F a flux addition. Getting the breaking class right for the ambient temperature and aggregate is the difference between a tack coat that holds and one that is still wet when the paver arrives.

Air is blown through hot bitumen to raise the softening point and reduce temperature susceptibility, producing a binder that stays in place on a vertical surface and through a hot summer. These are industrial rather than paving products and are specified under EN 13304 and EN 13305.

The designation reads softening point first, penetration second — R 85/25 is a binder with a softening point around 85 °C and penetration around 25. Buyers occasionally read it the other way round and order a product that will not do the job, so we confirm the intended application on every enquiry.