What are the main grades of CRMB specified in this code?

Three grades are specified: CRMB 50, CRMB 55, and CRMB 60, primarily distinguished by their minimum softening point (Clause 4).

What is the minimum Elastic Recovery required for CRMB?

A minimum of 50% elastic recovery of half thread at 15°C is required for all grades, indicating its flexible nature (Table 1).

What is the main purpose of the 'Separation' test?

The 'Separation' test checks the storage stability of CRMB. It ensures the rubber and bitumen remain a homogenous blend by limiting the difference in softening point between top and bottom samples to 4°C (Table 1).

Which grade is suitable for hotter climates?

CRMB 60, with the highest minimum softening point of 60°C, is recommended for use in very hot climatic regions (Table A-1).

IS 16868

: 2019

Crumb Rubber Modified Bitumen (CRMB) - Specification

CurrentFrequently UsedSpecificationTransportation · Roads and Pavement

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This standard specifies the requirements, testing methods, and grading for Crumb Rubber Modified Bitumen (CRMB) used in pavement construction. It defines three grades (CRMB 50, CRMB 55, CRMB 60) based on properties like softening point and penetration. The code ensures the quality and performance of bitumen modified with crumb rubber for enhanced road durability and flexibility.

Specifies requirements for different grades of crumb rubber modified bitumen (CRMB) used in flexible pavement construction for improved durability.

Quick Reference Values

Softening Point, Min for CRMB 5555 °C

Softening Point, Min for CRMB 6060 °C

Penetration at 25°C for CRMB 5550-60 (0.1 mm)

Elastic Recovery of half thread at 15°C, Min50 %

Separation, difference in softening point, Max4 °C

Viscosity at 150°C for CRMB 551-3 Pa.s

Flash Point (Cleveland Open Cup), Min220 °C

Practical Notes

The grade of CRMB (50, 55, 60) should be selected based on the region's climate and expected traffic loads, as guided by Annex A.

Higher mixing and laying temperatures are required for CRMB compared to conventional bitumen; strict temperature control is crucial for workability and performance.

The 'Separation' test is critical to ensure storage stability and prevent the rubber particles from separating from the bitumen, which would negate the benefits of modification.