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IRC SP 107 : 2015

Guidelines for Gap Graded Rubberized Bitumen Mix Surfacing

ASTM D6114
CurrentSpecializedCode of PracticeTransportation · Roads and Pavement
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Summary

IRC SP:107 covers rubberized gap-graded bituminous wearing course — using crumb rubber from waste tyres. Promotes waste tyre recycling while providing a durable, crack-resistant wearing course. Government mandates crumb rubber use on certain NH stretches.

Guidelines for use of crumb rubber from waste tyres in gap-graded bituminous wearing course — an eco-friendly pavement solution.

Key Values
Crumb rubber content15-20% by weight of bitumen
Blending temperature170-190°C
Mix thickness20-25mm (thin wearing course)
Practical Notes
! Government mandates crumb rubber use on certain NH to address waste tyre problem.
! Gap-graded rubberized mix provides excellent crack reflection resistance — ideal for overlays.
! Higher construction temperature (170-190°C vs 150-160°C) — needs modified equipment.
! Crumb rubber must be blended into bitumen BEFORE adding to mix — dry mixing does not work.
! Storage time of CRMB limited to 24 hours — must be used fresh.
! India generates ~1 million tonnes of waste tyres annually — rubberized roads provide sustainable disposal.
! Ensure uniform dispersion of crumb rubber in bitumen; inadequate mixing can lead to performance issues. Consider using a high-shear mixer.
! The addition of crumb rubber can increase bitumen viscosity significantly. Adjust mixing and compaction temperatures accordingly to avoid premature cooling or overheating.
! Pre-treatment of crumb rubber (e.g., sieving) to remove fines or oversized particles is crucial for consistent results.
! Always perform laboratory trials with the actual materials proposed for the project. Local aggregate characteristics can vary widely.
! Monitor the temperature of the mix closely during transport and paving. Hotter temperatures are needed compared to conventional mixes.
! Compaction is critical. Ensure pavers have adequate screed heating and vibratory rollers are used efficiently within the specified temperature window.
! Consider the potential for increased fume generation during mixing and paving. Adequate ventilation and personal protective equipment are essential.
! The use of adhesion promoters might be necessary, especially if aggregates have a known tendency for moisture susceptibility, even with crumb rubber modification.
! Regular calibration of asphalt plants, particularly the bitumen and crumb rubber feeding systems, is paramount for achieving the specified binder content.
! Field trials are highly recommended for new projects to fine-tune the mix design and construction procedures based on site conditions.
! The rheological properties of CRM bitumen are altered; consider this for performance prediction under varying climatic conditions.
! When sourcing crumb rubber, ensure it meets the particle size distribution specified in the code to avoid issues with workability and aggregate interlocking.
! The increased binder film thickness in gap-graded mixes offers better coating but requires careful control of binder content to prevent pavement bleeding.
! Moisture damage potential needs to be assessed through laboratory testing, as the interaction of crumb rubber with aggregates and bitumen can influence this.
! For PMGSY roads, where resources might be constrained, understanding the principles of this code can guide the selection of appropriate binder and aggregate combinations for durable rural roads.
Cross-Referenced Codes
IS 16868:2019Crumb Rubber Modified Bitumen (CRMB) - Specif...
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IRC 37:2018Guidelines for the Design of Flexible Pavemen...
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rubberized bitumencrumb rubbergap gradedwaste tyreeco-friendlyIRC SP
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Similar International Standards
ASTM D6114ASTM (US)
HighCurrent
Standard Specification for Asphalt-Rubber Binder
Both cover crumb rubber modified bitumen/asphalt with similar rubber content ranges.
Key Differences
Key Similarities
≈Both specify 15-20% crumb rubber by weight of bitumen binder.
Parameter Comparison
ParameterIS ValueInternationalSource
⚠ Verify details from original standards before use
Quick Reference Values
Crumb rubber content15-20% by weight of bitumen
Blending temperature170-190°C
Mix thickness20-25mm (thin wearing course)
Aggregate gradationGap-graded (similar to SMA)
Binder content7.0-8.5% (higher than conventional)
Air voids4-6%
Crumb rubber sizePassing 2mm, retained on 0.3mm
Minimum crumb rubber content (by weight of bitumen)8%
Maximum crumb rubber content (by weight of bitumen)20%
Crumb rubber particle size distribution (passing 0.075 mm sieve)<= 10%
Crumb rubber particle size distribution (retained on 2.36 mm sieve)<= 10%
Softening Point of Crumb Rubber Modified Bitumen (CRM Bitumen)>= 50°C (Ring and Ball Test)
Ductility of CRM Bitumen (at 25°C)>= 20 cm
Viscosity of CRM Bitumen (at 60°C)>= 3 Pa.s
Target Binder Content (for VG-30 bitumen)5.0 - 6.5% by weight of mix
Target Binder Content (for VG-40 bitumen)4.8 - 6.3% by weight of mix
Optimum Compaction Temperature (for mix)160°C - 175°C
Mixing Temperature (for mix)170°C - 180°C
Minimum aggregate crushing value25%
Maximum aggregate impact value20%
Minimum aggregate abrasion value40%
Water absorption of coarse aggregate<= 2%
Plasticity Index of Fine Aggregate<= 8%
Stripping value of aggregate (with bitumen)<= 10%
Required Minimum Service Life10 years
Key Formulas
CRMB preparation: bitumen + 15-20% crumb rubber at 170-190°C for 1-2 hours
Marshall stability: min 6 kN at 60°C
Flow: 2-4mm
Flow = (Load at failure - Load at 0.5 mm) / (Slope of load vs. deformation curve in initial range)
VMA = (VFA * VFB) / 100 + VMA
VFA = (VMA - VIM) / VMA * 100
VFB = (VMA - VIM) / VMA * 100
Voids in Mineral Aggregate (VMA) = 100 - (Gmb * % Aggregate)
Binder Content (by weight of mix) = (Gmb * % Binder) / Gmb
Key Tables
Table 1 — Gap-graded rubberized mix gradation
Table 2 — Mix design requirements
Table 1 — Grading of Crumb Rubber
Table 2 — Properties of Crumb Rubber Modified Bitumen
Table 3 — Properties of Aggregates
Table 4 — Gradation Limits for Gap-Graded Mixes (Nominal Maximum Size 13.2 mm)
Table 5 — Gradation Limits for Gap-Graded Mixes (Nominal Maximum Size 10 mm)
Table 6 — Marshall Design Criteria
Key Clauses
Cl. 3 — Crumb rubber specifications
Cl. 4 — Gap-graded mix design
Cl. 5 — Binder-rubber interaction
Cl. 6 — Construction temperature (higher than conventional)
Cl. 3.1 — Materials: Crumb Rubber
Cl. 3.2 — Materials: Bitumen
Cl. 3.3 — Materials: Aggregates
Cl. 4.1 — Mix Design Procedure
Cl. 4.2 — Determination of Optimum Binder Content
Cl. 4.3 — Marshall Mix Design
Cl. 5.1 — Construction Equipment
Cl. 6.1 — Quality Control
Cl. 7.1 — Environmental Considerations
Why use crumb rubber in roads?+
Two benefits: 1) Sustainable disposal of waste tyres (India: 1M tonnes/year), 2) Better pavement — rubberized bitumen has 2-3× better fatigue life and superior crack resistance vs plain VG bitumen.
Gap-graded rubberized vs SMA?+
Both are gap-graded premium mixes. Rubberized uses crumb rubber in binder (15-20%). SMA uses polymer/fibre. Rubberized has better crack resistance; SMA better rutting resistance. Both cost more than BC.
Challenges with rubberized mixes?+
1) Higher temperature (worker safety), 2) Limited CRMB storage life (24h), 3) Specialized blending equipment, 4) Variable crumb rubber quality, 5) Contractor training needed.
What is the primary advantage of using crumb rubberized bitumen mixes as per IRC SP 107:2015?+
The primary advantage is environmental sustainability by utilizing waste tires, reducing landfill burden and conserving virgin resources. Additionally, these mixes often exhibit improved performance characteristics like enhanced durability, better resistance to rutting and cracking, and reduced noise pollution compared to conventional mixes.
What are the different types of crumb rubber and their applications in this code?+
IRC SP 107:2015 specifies using crumb rubber derived from waste tires. It's categorized based on particle size distribution. The code primarily focuses on using this crumb rubber as a modifier to bitumen, creating Crumb Rubber Modified Bitumen (CRM Bitumen), which is then used in gap-graded bituminous wearing courses.
What is the recommended percentage of crumb rubber to be used in the mix?+
The code suggests a minimum crumb rubber content of 8% by weight of bitumen for producing CRM Bitumen. The maximum recommended content is 20% by weight of bitumen. The exact percentage is determined during the mix design process based on desired performance and material properties.
How does crumb rubber affect the properties of bitumen and the final mix?+
Crumb rubber modifies the rheological properties of bitumen, increasing its viscosity, softening point, and elasticity. This leads to a stiffer binder at high temperatures, reducing rutting, and a more elastic binder at low temperatures, improving resistance to thermal cracking. The gap-graded aggregate structure also contributes to enhanced performance.
What are the key requirements for aggregates used in gap-graded rubberized bitumen mixes?+
Aggregates must meet stringent requirements for crushing strength, impact, abrasion, and flakiness/elongation. They should have low water absorption and clean surfaces. The gradation is critical, being 'gap-graded' with intentionally omitted sieve sizes, which allows for better bitumen coating and interlocking of aggregates.
What is the typical binder content for these mixes, and why is it important?+
The target binder content is generally higher than conventional dense graded mixes due to the gap-graded aggregate structure. For VG-30 bitumen, it typically ranges from 5.0% to 6.5% by weight of the mix, and for VG-40, it's 4.8% to 6.3%. This higher binder content ensures adequate coating of aggregates and forms a mastic-like binder film, crucial for durability.
What are the critical temperatures for mixing and compaction of these mixes?+
The mixing temperature is generally higher than conventional mixes, typically between 170°C and 180°C, to ensure proper blending of bitumen and crumb rubber. The compaction temperature window is also crucial and usually ranges from 160°C to 175°C. Overheating or cooling can compromise the mix quality and performance.
What are the key Marshall mix design criteria according to IRC SP 107:2015?+
The Marshall mix design criteria include parameters like stability, flow, VMA (Voids in Mineral Aggregate), VFA (Voids Filled with Asphalt), and VIM (Voids in Total Mix). The code specifies acceptable ranges for these parameters for different nominal maximum aggregate sizes to ensure adequate strength, durability, and air voids in the compacted pavement layer.
How is quality control performed for crumb rubberized bitumen mixes on-site?+
Quality control involves regular checks on incoming materials (crumb rubber, bitumen, aggregates), monitoring plant operations (temperatures, binder and crumb rubber feed rates), and field testing. This includes density tests, temperature checks during paving and compaction, and potentially periodic extraction of samples for laboratory verification of mix properties.
Are there any special considerations for environmental aspects or safety during construction?+
Yes, the code emphasizes environmental benefits by recycling waste tires. However, during construction, higher temperatures can lead to increased fume generation. Adequate ventilation at the plant and in work areas, along with appropriate personal protective equipment (PPE) for workers, is essential for safety and health.
What is the expected service life of pavements constructed using these guidelines?+
The guidelines are aimed at providing an eco-friendly and durable pavement solution. The expected minimum service life for a properly constructed wearing course using these rubberized bitumen mixes is typically around 10 years, offering good performance and longevity under Indian traffic conditions.
Can this type of mix be used for all types of roads in India?+
IRC SP 107:2015 provides guidelines for its use in the wearing course. While primarily intended for highway applications (National Highways, State Highways), its principles can be adapted for other roads like Urban Roads or even under specific project conditions for rural roads managed by agencies like NHAI, MoRTH, or PMGSY, provided the traffic and environmental conditions are suitable and the design is validated.