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.
| Property | Value Range | Standard |
|---|---|---|
| Specific Gravity | 0.51-1.2 | Varies with particle size |
| Bulk Density | 524-1,273 kg/m³ | Higher for finer particles |
| Particle Shape | Irregular (ambient) to angular (cryogenic) | Depends on grinding method |
| Surface Texture | Rough/porous (ambient) to smooth (cryogenic) | Affects bonding in applications |
| Moisture Content | <0.75% | ASTM D5603 |
| Free Metal Content | <0.01% | ASTM D5603 |
| Fiber Content | <0.5% (coarse); <0.1% (fine) | ASTM D5603 |
Beyond definitions
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How to read this table
- Each row is one physical property; Value Range gives the typical range across all mesh sizes; Standard gives the test method or specification limit from ASTM D5603.
- Moisture Content, Free Metal Content, and Fibre Content rows show ASTM D5603 maximum limits — these are go/no-go specification limits, not typical values.
- Specific Gravity and Bulk Density ranges are wide because they vary significantly with mesh size — narrow to the specific mesh grade when planning storage calculations.
About this table
Crumb rubber is graded and sold against a defined set of physical properties — and buyers of certified crumb rubber specify these parameters in purchase orders and require a Certificate of Analysis against ASTM D5603 for each batch. This table covers the seven key physical properties, their typical value ranges, and the applicable standard or standard-driven limit for each.
Specific Gravity varies from 0.51 to 1.2 depending on particle size and grinding method — this wide range reflects the difference between very coarse crumb rubber (lower apparent density) and fine rubber powder. In practice, a given mesh band (e.g., 30-mesh crumb rubber) will have a narrower specific gravity range. Bulk Density is the more practically useful figure for storage and transport planning, ranging from 524 to 1,273 kg/m³ across the full mesh range — finer particles pack more densely because the small particles fill void spaces between larger ones.
Particle Shape is a quality differentiator between grinding methods: ambient (mechanical) grinding produces irregular, fibrous-edged particles, while cryogenic grinding produces angular, clean-edge particles. The surface texture follows the same pattern — ambient grinding produces rough, porous particles with high surface area (better for bonding in some applications), while cryogenic produces smooth particles. Moisture Content below 0.75% is the ASTM D5603 limit — crumb rubber absorbs atmospheric moisture, so storage and packaging conditions after production directly affect moisture compliance. Free Metal Content below 0.01% (100 ppm) reflects the requirement that residual steel from tyre belt wires is essentially eliminated by the magnetic separation stage. Fibre Content limits differ by particle coarseness: coarse crumb rubber (10-mesh) allows up to 0.5% textile fibre, while fine rubber powder (80-mesh) must be below 0.1% — finer particles have more surface area and fibre contamination is more disruptive to end-use performance at fine mesh.
Key insights
- Moisture content below 0.75% (ASTM D5603) is a production and packaging discipline — crumb rubber produced at spec can absorb moisture in storage if bags are not sealed properly after production.
- Free metal content below 0.01% is the most machine-sensitive spec — residual steel wire in crumb rubber damages downstream buyer equipment and is cause for immediate lot rejection.
- Particle shape (rough ambient vs smooth cryogenic) affects bonding behaviour in end-use applications — CRMB production benefits from rough-surface ambient-ground crumb rubber that bonds more effectively with bitumen.
- Fibre content limits differ by mesh — coarser crumb rubber (10-mesh) allows 5x more fibre than fine powder (80-mesh), reflecting that fibre contamination is harder to remove and more impactful at finer particle sizes.
Methodology & sources
Physical property ranges are based on ASTM D5603 classification criteria and published crumb rubber product data as of 2024. Specific gravity and bulk density values span the full mesh range (10-mesh coarse to 80-mesh fine); actual values for a specific mesh grade will be narrower. ASTM D5603 is updated periodically — verify current specification limits with the latest ASTM publication.
Related data tables
Crumb rubber mesh-band output from an ambient grinding line
Yield share, particle size range, primary application, and indicative price for the four mesh bands — coarse, mid-coarse, fine, and ultra-fine — that an ambient grinding line produces from waste tyres.
Crumb rubber specification sheet by mesh and grinding method
ASTM D5603 pass-or-fail specification limits for crumb rubber across four mesh bands — covering specific gravity, bulk density, moisture, free metal, and fibre content — the reference standard for batch certificate of analysis and offtake agreements.
Quality Control Testing Methods and Standards
Six quality control testing standards used in tyre recycling — covering ASTM standards for crumb rubber and reclaimed rubber, IS 15462 and IRC SP:53 for Indian CRMB certification, and ASTM D6114 for international CRMB qualification.