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IS 16868:2019 is the Indian Standard (BIS) for crumb rubber modified bitumen (crmb) - specification. 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.
! 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.
Directly specifies requirements for binders produced by reacting asphalt with ground tire rubber.
Austroads AGPT/T190-19Austroads, Australia / New Zealand
MediumCurrent
Specification Framework for Polymer Modified Binders
Provides a performance-based framework that includes specific classes for crumb rubber modified binders (e.g., A10R, A15R).
AASHTO M 332-14 (2019)AASHTO, USA
MediumCurrent
Standard Specification for Performance-Graded Asphalt Binder Using Multiple Stress Creep Recovery (MSCR)
A performance-based specification where crumb rubber is a common modifier used to meet high-performance criteria, though it's not explicitly named.
EN 14023:2010CEN (European Committee for Standardization), Europe
LowCurrent
Bitumen and bituminous binders - Specification framework for polymer modified bitumens
A general framework for specifying all types of Polymer Modified Bitumens (PMBs), under which CRMB could be specified via national annexes.
Key Differences
≠IS 16868 uses an empirical grading system (CRMB 50, 55, 60) based on softening point, whereas modern international standards like AASHTO M 332 use a Performance Graded (PG) system based on rheological performance at climate-specific temperatures.
≠The key test for elasticity in IS 16868 is 'Elastic Recovery of half thread'. In contrast, AASHTO M 332 uses the 'Multiple Stress Creep Recovery (MSCR)' test, which is considered more effective at predicting pavement rutting performance.
≠IS 16868 specifies the grading of the crumb rubber raw material within the standard. Performance-based standards like AASHTO M 332 are agnostic to the formulation, focusing only on the final properties of the binder.
≠The storage stability requirement in IS 16868 (Max 4°C difference in softening point) is less stringent than in ASTM D6114 (Max 2°C difference), indicating different expectations for binder homogeneity after hot storage.
Key Similarities
≈All standards share the primary objective of enhancing asphalt binder properties using crumb rubber to improve pavement resistance to rutting (permanent deformation) and cracking.
≈Core physical property tests such as Softening Point (Ring & Ball), Penetration, and Flash Point are included in both IS 16868 and equivalent empirical standards like ASTM D6114, serving as fundamental quality control checks.
≈All specifications include a requirement to ensure stability during hot storage, typically measured by the difference in softening point between the top and bottom samples of a conditioned tube, to prevent phase separation.
≈Control of high-temperature viscosity is a common requirement across all standards to ensure the binder is sufficiently fluid for proper mixing with aggregate and for paving operations.
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).