IRC SP:53 specification sheet — CRMB 55 and CRMB 60
Eight-parameter IRC SP:53 pass-or-fail specification sheet for CRMB 55 and CRMB 60 grades, covering softening point, penetration, elastic recovery, flash point, viscosity, storage stability, loss on heating, and penetration retention after thin film oven test.
| Parameter | CRMB 55 specification | CRMB 60 specification | Test method |
|---|---|---|---|
| Softening point | Minimum 55 °C | Minimum 60 °C | Ring-and-ball, IS 1205 |
| Penetration at 25 °C | 50 to 70 decimillimetres | 30 to 50 decimillimetres | IS 1203 |
| Elastic recovery at 15 °C | Minimum 50% | Minimum 70% | Ductilometer, IS 15462 |
| Flash point | Minimum 220 °C | Minimum 220 °C | Cleveland Open Cup, IS 1209 |
| Viscosity at 150 °C | Minimum 3 poise | Minimum 5 poise | Brookfield viscometer |
| Separation of softening point (48-hour storage stability) | Maximum 3 °C | Maximum 3 °C | IRC SP:53 method |
| Loss on heating at 163 °C | Maximum 1.0% | Maximum 1.0% | IS 1212 |
| Penetration after thin film oven test | Minimum 60% retained | Minimum 65% retained | IS 9382 / IS 1203 |
Beyond definitions
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How to read this table
- All values are minimum requirements unless labelled as maximum — e.g. softening point is a minimum, penetration is a range, storage stability separation is a maximum
- Test methods reference Indian Standards (IS) — the IS method is mandatory for CRMB sold under Indian procurement contracts; ASTM or BS equivalents are not interchangeable without buyer approval
- Elastic recovery is the most sensitive production parameter — a batch that meets softening point but fails elastic recovery typically indicates insufficient crumb rubber dose or poor dispersion quality
- Both grades share the same flash point, storage stability, loss on heating, and penetration retention limits — the differentiation between grades is in softening point, penetration range, elastic recovery, and viscosity
About this table
Crumb Rubber Modified Bitumen (CRMB) sold to Indian road construction buyers must conform to the Indian Roads Congress specification IRC SP:53, which defines two commercial grades — CRMB 55 for standard highway wearing courses and CRMB 60 for high-stress applications such as airports, bridge decks, and heavy-traffic corridors. Every production batch must be tested against eight pass-or-fail parameters before dispatch, and the batch certificate of analysis (COA) referencing specific Indian Standard (IS) test methods must accompany each delivery. This table presents the full specification sheet for both grades side by side.
The softening point is the grade-defining parameter — CRMB 55 must achieve a minimum ring-and-ball softening point of 55 degrees Celsius, CRMB 60 must reach 60 degrees. Softening point is the most direct indicator of the rubber content and quality of dispersion in the binder; low softening point is typically the first failure mode when rubber content is insufficient or when the colloid mill has not achieved adequate particle break-up. Penetration at 25 degrees Celsius is the inverse measure — CRMB 55 allows a wider penetration range (50 to 70 dmm) than CRMB 60 (30 to 50 dmm), reflecting CRMB 60's stiffer binder requirement for high-load applications.
Elastic recovery at 15 degrees Celsius is the parameter that most clearly differentiates rubber-modified binder from plain bitumen. CRMB 55 requires a minimum of 50 percent recovery; CRMB 60 requires 70 percent. This test is measured using a ductilometer (IS 15462) and directly reflects the rubber network's ability to return to shape after deformation — the property that gives rubberised roads their resistance to rutting and thermal cracking. Both grades share the same flash point minimum (220 degrees Celsius), the same storage stability tolerance (maximum 3 degrees Celsius softening point separation after 48-hour storage), and the same loss-on-heating limit (maximum 1.0 percent at 163 degrees Celsius). Viscosity at 150 degrees Celsius is the pumpability and laydown specification — CRMB 60 requires a higher minimum viscosity (5 poise versus 3 poise for CRMB 55) because its higher rubber content produces a stiffer hot binder.
Use this table as the QC reference for daily production batch testing, and as the foundation for drafting offtake contract specifications with NHAI contractors or state Public Works Department procurement officers. The CRMB Buyer Segments table provides the commercial context for which grade each buyer typically specifies.
Key insights
- Elastic recovery is the most discriminating parameter — CRMB 60 requires 70 percent minimum versus 50 percent for CRMB 55, reflecting the higher rubber dose and dispersion quality needed for airport and bridge-deck applications
- Storage stability (maximum 3 degrees Celsius softening point separation after 48 hours) is the parameter that catches phase-separation problems — a batch that passes softening point at production but separates in the tanker will fail at the buyer's plant
- Viscosity at 150 degrees Celsius for CRMB 60 (minimum 5 poise) is higher than for CRMB 55 (minimum 3 poise) — batch recipe and colloid mill settings must be adjusted separately for each grade
- Both grades require penetration retention of at least 60 percent (CRMB 55) or 65 percent (CRMB 60) after the thin film oven test, confirming durability under long-term heat exposure
- A single failing parameter is sufficient to reject the entire batch — testing all eight parameters before dispatch is non-negotiable for serious supply relationships
Methodology & sources
Specifications are from IRC SP:53 (latest edition as of 2024). Test methods reference the Indian Standard (IS) equivalents as specified in IRC SP:53. CRMB grade boundaries and test protocols are subject to revision by the Indian Roads Congress; verify against the current published edition before using these figures as the sole basis for a supply contract.
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