Crumb Rubber Physical Specs by Source and Mesh
The physical properties that crumb rubber buyers test on every purchase order — specific gravity, bulk density, particle shape differences between ambient and cryogenic grinding, and the moisture, metal, and fibre purity limits.
| Property | Spec Range | Notes |
|---|---|---|
| Specific Gravity | 0.51 to 1.2 | Depends on particle size and grinding method |
| Bulk Density | 524 to 1,273 kilograms per cubic metre | Finer particles pack denser |
| Particle Shape — Ambient Grinding | Irregular, rough, porous | Produced by room-temperature mechanical grinding |
| Particle Shape — Cryogenic Grinding | Angular, smooth-faced | Produced after liquid-nitrogen pre-cooling |
| Moisture Content | Below 0.75 percent | Per ASTM D5603 |
| Free Metal Content | Below 0.01 percent | Magnetic separation must achieve this limit |
| Fibre Content — Coarse Grades | Below 0.5 percent | For 4 to 30 mesh particle ranges |
| Fibre Content — Fine Grades | Below 0.1 percent | For 40 mesh and finer; air classification required |
Beyond definitions
Planning to start a Tyre Recycling business?
Get the full business understanding — capex, regulations, machinery, vendor questions, and risk checks before you commit capital.
How to read this table
- Blue rows = density and shape properties; cyan = purity limits; amber = fibre content limits by grade
- All moisture, metal, and fibre limits are maximum upper bounds — lower is better
- ASTM D5603 governs crumb rubber classification — the moisture test is the most commonly cited method on purchase orders
- Fibre limits apply based on mesh size of the product being sold, not the process used
About this table
When a crumb rubber buyer — whether an asphalt contractor, playground installer, or rubber compounder — places a purchase order, they will verify a set of physical properties before accepting the shipment. These are not aspirational quality targets; failing even one of them can result in rejection of the full batch. Understanding them is essential for anyone setting up a crumb rubber grinding operation.
Specific gravity ranges from 0.51 to 1.2 depending on particle size and the amount of carbon black and inorganic filler in the source tyre — this wide range is expected, not a defect. Bulk density runs from 524 to 1,273 kg/m³: finer particles pack more densely, so a bulk density measurement also tells you something about the particle size distribution. Both properties are used by buyers to verify batch-to-batch consistency.
Particle shape depends entirely on the grinding method. Ambient grinding (room-temperature mechanical shredding and milling) produces irregular, rough, porous particles with high surface area — beneficial for asphalt bonding but variable in packing. Cryogenic grinding (pre-cooling the rubber in liquid nitrogen before grinding) produces angular, smooth-faced particles with tighter size distribution — preferred for fine applications like sealants and compound fillers but significantly more expensive per kilogram to produce.
The three purity limits are where most quality rejections happen. Moisture content must stay below 0.75% per ASTM D5603 — excess moisture causes compounding defects and mould deposits. Free metal content must be below 0.01% — magnetic separation equipment must be calibrated and operating correctly on every production run. Fibre content limits differ sharply by grade: coarse grades (4–30 mesh) are allowed up to 0.5% fibre, but fine grades (40 mesh and above) must stay below 0.1%, which typically requires air classification in addition to mechanical separation.
Key insights
- Fine grades (40 mesh and above) require fibre content below 0.1% — tighter than coarse grades by 5 times — and typically require air classification equipment to achieve this
- Free metal must be below 0.01% — magnetic separators must be verified in calibration on every production run, not just during commissioning
- Ambient and cryogenic grinding produce fundamentally different particle shapes — operators cannot substitute one for the other when a buyer specifies particle morphology
- Bulk density range (524–1,273 kg/m³) is extremely wide because it depends on particle size — a bulk density measurement serves as a secondary particle-size check
- Moisture above 0.75% is a rejection trigger — drying equipment or covered storage is not optional for operations in humid climates
Methodology & sources
Physical specification ranges are based on ASTM D5603 (Rubber from Recycled Tires — Sampling and Testing) and common Indian buyer acceptance criteria as of 2024. Specific gravity and bulk density ranges reflect the full spectrum of particle sizes (4 mesh to 100+ mesh); individual grades have narrower ranges within these bounds. Moisture, metal, and fibre limits are widely referenced but individual buyers may specify tighter tolerances.
Related data tables
Crumb Rubber Physical Properties
Seven physical properties of crumb rubber that buyers verify on every purchase order — specific gravity, bulk density, particle shape, surface texture, moisture content, free metal content, and fibre content — with ASTM D5603 specifications.
Grinding Methods Comparison
A five-method comparison of tyre grinding technologies — mechanical ambient, cryogenic, wet grinding, micro-milling, and water jet — showing achievable particle size, temperature requirements, primary advantage, and primary limitation for each.
Tyre Recycling End Products — Cross-product Comparison
Side-by-side comparison of nine tyre recycling outputs across three product families — crumb rubber grades, CRMB road-bitumen blends, and reclaimed rubber tiers — showing mesh or dose, buyers, capex tier, and discount versus virgin for each.