How end-of-life tyres become crumb rubber, how it is blended into bitumen, and which penetration-grade bitumen is used as the base binder.
How Rubberized Asphalt Is Made From Millions of Old Tyres
Rubberized asphalt replaces part of the paving binder with crumb rubber ground from scrap tyres. The rubber does not go straight from the tyre to the road — it passes through a recycling plant that shreds, de-steels, grinds and screens it, and it is then reacted into hot penetration-grade bitumen. This insight walks through that chain and states plainly which bitumen grade sits underneath it.
Last reviewed: 2026-10-24. Publisher: PetroBind Global.
What rubberized asphalt actually is
Rubberized asphalt — also called asphalt rubber or crumb rubber modified (CRM) asphalt — is an ordinary hot-mix asphalt pavement in which the bitumen binder has been modified with ground rubber recovered from end-of-life tyres. The rubber, once digested into the hot bitumen, raises the binder's viscosity, elasticity and high-temperature stiffness while keeping it flexible at low temperature. The aggregate, the paver and the roller are the same as a conventional job; the difference is entirely in the binder. ASTM D6114 is the specification most often cited for the asphalt-rubber binder itself.
Where the rubber comes from — the tyre-recycling plant
Scrap tyres do not arrive at the asphalt plant as usable material. They are processed first at a dedicated recycling facility. A typical passenger tyre yields roughly 9–12 kg of recoverable rubber, and a single lane-mile of rubberized asphalt overlay consumes on the order of 1,500–2,000 scrap tyres — which is why the material is described as diverting millions of tyres from stockpiles and landfill. Inside the plant the tyres move through a fixed sequence of size-reduction and separation steps before anything is ready to blend.
- Sorting and de-rimming — tyres are inspected and any steel rims removed.
- Primary shredding — tyres are cut into rubber chips around 50 mm across.
- Steel and fibre liberation — magnets pull out the steel belt and bead wire; textile fibre is removed by aspiration and screening.
- Granulation and grinding — cracker mills and granulators reduce the chips to crumb. Ambient grinding (at room temperature) gives an irregular, high-surface-area particle that reacts well with bitumen; cryogenic grinding (rubber frozen with liquid nitrogen) shatters it into smoother particles and is used less often for asphalt.
- Screening and classification — the crumb is sieved to a controlled particle size, typically 16 to 30 mesh (about 0.6–1.2 mm) for asphalt use, then bagged or stored in bulk.
Same diagram, for reference alongside the step list below.
How the crumb rubber gets into the bitumen
There are three routes, and they differ in how much rubber is used, where the mixing happens, and whether the result can be stored.
- Wet process (asphalt rubber): 15–22% crumb rubber by weight of the binder is blended into hot bitumen at roughly 190–218 °C and reacted for 45–60 minutes so the rubber swells by absorbing the bitumen's aromatic oils. It is usually blended on or near the paving site and used within hours. This is the ASTM D6114 / McDonald technology route.
- Terminal blend: a lower dose (around 5–12%) is fully digested at a refinery or asphalt terminal into a storage-stable binder that ships and handles like a normal polymer-modified bitumen.
- Dry process: 1–3% rubber by weight of the total mix is added as a partial aggregate substitute directly at the mixer, without pre-reacting it with the binder. It is the least common and least predictable of the three.
Which bitumen is used as the base binder
The feedstock is a standard, unmodified penetration-grade paving bitumen — most commonly 60/70 or 80/100 pen (equivalent performance grades such as PG 58-22 or PG 64-16 are used where Superpave grading applies). A softer base grade like 80/100 is often preferred as the starting point because adding 15–22% rubber stiffens the binder substantially, so the blender wants penetration headroom; in consistently hot climates a 60/70 base is used instead. The rubber itself is the modifier, so the base is normally a plain paving grade rather than an already polymer-modified (SBS) bitumen — although hybrid rubber-plus-polymer binders do exist for demanding jobs. Because the reacted binder is more viscous, gap-graded asphalt-rubber mixes also carry a higher binder content (around 7.5–9%) than a conventional dense-graded mix (around 5–6%).
- Base grade: penetration-grade bitumen, typically 60/70 or 80/100 pen.
- Not typically a pre-modified PMB — the crumb rubber provides the modification.
- Softer (higher-pen) base grades give room for the stiffening the rubber adds.
- Binder content in the finished mix is usually higher than a conventional mix.
Why agencies specify it
The reacted rubber binder improves fatigue life and resistance to reflective and thermal cracking, holds up against rutting in heat, and allows thinner overlays. Gap-graded and open-graded rubberized surfaces also cut tyre-road noise by roughly 3–5 dB compared with conventional dense-graded asphalt. Set against that are a higher binder cost, tighter temperature control during blending and laying, and — for the wet process — a short working window. The environmental argument is straightforward: the material consumes scrap tyres that would otherwise be stockpiled or landfilled.
Where PetroBind fits
PetroBind supplies the base binder, not the rubber or the finished blend. If your operation runs a wet-process or terminal-blend programme and needs penetration-grade bitumen (60/70, 80/100) as the feedstock, that is a standard RFQ — grade, quantity, destination port, packing and Incoterm, with COA and PDS on the confirmed lot. PetroBind does not supply crumb rubber, asphalt-rubber binder, or pre-blended CRM asphalt.
Frequently Asked Questions
- Q: What kind of bitumen is used to make rubberized asphalt?
- A: A standard penetration-grade paving bitumen — most commonly 60/70 or 80/100 pen (or an equivalent performance grade such as PG 58-22 / PG 64-16). It is normally an unmodified grade, because the crumb rubber is what modifies it. A softer, higher-penetration base is often chosen so there is room for the stiffening that 15–22% rubber adds.
- Q: How many old tyres go into rubberized asphalt?
- A: Roughly 1,500–2,000 scrap tyres per lane-mile of overlay, depending on layer thickness and rubber dose. A passenger tyre yields about 9–12 kg of recoverable rubber after the steel and fibre are removed.
- Q: What is the difference between the wet process and terminal blend?
- A: The wet process blends 15–22% crumb rubber into hot bitumen on or near the paving site and reacts it for 45–60 minutes; the binder must be used within hours. A terminal blend digests a smaller dose (around 5–12%) at a refinery or terminal into a storage-stable binder that ships and handles like a normal modified bitumen.
- Q: Does PetroBind supply crumb rubber or rubberized asphalt binder?
- A: No. PetroBind supplies the base penetration-grade bitumen (for example 60/70 or 80/100) that a blender uses as feedstock. It does not supply crumb rubber, asphalt-rubber binder, or pre-blended CRM asphalt.