IRC SP 53 : 2010Guidelines on Use of Modified Bitumen in Road Construction

IRC SP 53 specifies guidelines on use of modified bitumen in road construction — Polymer Modified Bitumen (PMB), Crumb Rubber Modified Bitumen (CRMB), and natural rubber-modified bitumen used in flexible pavements where conventional VG-grade bitumen (IS 73:2013) is inadequate.

Use modified bitumen per IRC SP 53 when: - High-temperature service — pavement temperatures regularly > 50 °C; conventional VG-30/VG-40 ruts. Modified bitumen (PMB-40, PMB-70 grades) extends rutting resistance. - High-traffic corridors — > 1500 commercial vehicles per day, especially with heavy axle loads. PMB extends fatigue life by 30-50 %. - Cold-weather pavements — Ladakh, hill roads where conventional bitumen embrittles in winter. Polymer modification improves low-temperature flexibility. - Long-life pavements (perpetual pavement design) — 30-year design life requires modified bitumen for the structural layer. - Special applications — bridge deck waterproofing, airport runway, container yard pavement, bus terminals. - CRMB — sustainability projects using waste tyre rubber.

IRC SP 53 covers the *modified bitumen as a material*; it pairs with IRC:111:2009 for the *mix* design (modified bitumen used in BC / DBM / open-graded mixes) and IS 15462:2018 / IS 15469 for the product specification (the manufacturer's quality standard).

1. Polymer Modified Bitumen (PMB)

The most common modified bitumen in Indian highway practice. Two polymer families: - Plastomer (LDPE, EVA, PE wax) — improves stiffness at high temperature, rutting resistance - Elastomer (SBS, SBR, NBR) — improves elasticity, fatigue resistance, low-temperature performance

Most commercial PMB is SBS-modified (styrene-butadiene-styrene), giving balanced performance. Manufactured at refinery by hot-blending polymer (3-5 % by mass of bitumen) into base bitumen via high-shear mixer.

Grades (IRC SP 53 / IS 15462:2018): - PMB-40 — softening point ≥ 60 °C; for hot climates, heavy traffic - PMB-70 — softening point ≥ 70 °C; for very hot climates, very heavy traffic - PMB-25 — softening point ≥ 55 °C; for cold-zone applications (good low-T flex)

2. Crumb Rubber Modified Bitumen (CRMB)

Waste tyre rubber (granulated to 0.4-2.0 mm) blended with bitumen at 12-20 % by mass at high temperature with mechanical agitation. Sustainable — utilises waste tyres.

Grades (IS 15469): - CRMB-50 — softening point ≥ 50 °C; for moderate climates - CRMB-55 — softening point ≥ 55 °C; for hot climates - CRMB-60 — softening point ≥ 60 °C; for very hot climates and high traffic

3. Natural rubber-modified bitumen

Natural latex blended with bitumen. Less common in India; relevant where rubber industry is local.

4. Other modifiers — sulphur-extended bitumen, nano-modified bitumen — research / pilot scale, not in routine use.

PMB acceptance properties (per IS 15462:2018, tested per IRC SP 53):

| Property | PMB-40 | PMB-70 | PMB-25 | |---|---|---|---| | Penetration at 25 °C, 0.1 mm | 30-50 | 30-50 | 50-90 | | Softening point (°C, min) | 60 | 70 | 55 | | Viscosity at 150 °C, Pa·s | 0.3-0.7 | 0.5-1.2 | 0.2-0.5 | | Elastic recovery at 15 °C, % (min) | 50 | 70 | 70 | | Flash point (°C, min) | 220 | 220 | 220 | | Storage stability (softening point difference, °C, max) | 3 | 3 | 3 |

CRMB acceptance properties (per IS 15469):

| Property | CRMB-50 | CRMB-55 | CRMB-60 | |---|---|---|---| | Penetration at 25 °C, 0.1 mm | > 50 | > 40 | > 30 | | Softening point (°C, min) | 50 | 55 | 60 | | Elastic recovery at 25 °C, % (min) | 30 | 40 | 50 | | Crumb-rubber content (%) | 12-15 | 15-18 | 18-20 | | Flash point (°C, min) | 220 | 220 | 220 |

Tests after RTFOT (short-term ageing): - Mass loss ≤ 1.0 % - Increase in softening point ≤ 6 °C (PMB) / ≤ 8 °C (CRMB) - Loss of penetration ≤ 35 % - Loss of elastic recovery ≤ 10 %

Mix design with modified bitumen (IRC:111:2009): - Optimum binder content typically 0.2-0.5 % higher than conventional VG-30 mix - Marshall stability: typically 13-18 kN (vs 9-11 kN conventional) - Indirect tensile strength ratio (ITSR): ≥ 80 % - Rutting (Hamburg wheel-tracker, 50 °C, 20,000 passes): ≤ 4-6 mm (vs 6-10 mm conventional)

Cost premium: - PMB: 30-50 % over VG-30 (depends on polymer cost, season) - CRMB: 10-25 % over VG-30 (cheaper than PMB; sustainability angle) - Justification by life-cycle: PMB-50 pavement lasts 12-15 years vs VG-30 8-10 years on heavy traffic — 30-50 % NPV saving

• IRC:111:2009 — dense-graded bituminous mixes (BC, DBM with modified bitumen).
• IRC:37:2018 — flexible pavement design (modified bitumen recommended for high-traffic / hot-climate sections).
• IRC SP 98:2013 — waste plastic in hot bituminous mixes (an alternative to PMB).
• IRC SP 72:2015 — flexible pavement design for low-volume rural roads.
• IS 73:2013 — paving bitumen (the base bitumen before modification).
• IS 15462:2018 — polymer-modified bitumen specification.
• IS 15469 — crumb rubber modified bitumen specification.
• IS 383:2016 — aggregates.
• IS 1208 / IS 1205 / IS 1206 — penetration / softening point / viscosity test methods.
• MoRTH Specifications for Road and Bridge Works (5th Revision).

1. Specifying PMB without justification. PMB is 30-50 % more expensive; justify with traffic projection, climate data, and life-cycle cost analysis. Routine highway BC may not need PMB. 2. Wrong PMB grade for climate / traffic. PMB-25 in hot Rajasthan = inadequate (low softening point); PMB-70 in cold Ladakh = poor low-T flex. Match grade to climate. 3. Storage at refinery / depot too long. Modified bitumen settles (polymer separates) on long storage. Verify storage stability test (softening point difference < 3 °C). 4. Mixing PMB with non-compatible cement-bitumen at site. Some additives (lime, cement, anti-stripping) may interact with polymer chemistry. Test compatibility before site use. 5. Heating PMB above 175 °C. Polymer degrades at high temperature; viscosity rises, mix becomes harsh. Maintain PMB at 160-170 °C in storage tanks; never above 180 °C. 6. No project-specific trial mix. PMB performance in mix design is cement-and-aggregate-specific. Always do trial mix with project's actual materials before fixing dose. 7. CRMB plant distance > 50 km from supplier. CRMB cools / partially separates over long transport. Use a local plant or refinery nearby. 8. Marshall stability above 25 kN as a 'positive' result. Excessively stiff mix has poor fatigue life. PMB mix should be 13-18 kN — not higher. Higher means too much polymer or wrong grade. 9. Confusing PMB with CRMB on tender. They are different products with different price; specify clearly. 10. No quality verification at site. PMB tank delivery: spot-check softening point + viscosity + elastic recovery. Don't rely solely on supplier's certificate.

Standard cascade for flexible pavement using modified bitumen:

1. Pavement design (IRC:37:2018) — traffic, subgrade CBR → layer thicknesses. 2. Material strategy — VG-30 / VG-40 conventional vs PMB / CRMB modified, based on: - Traffic > 1500 CVPD: consider modified - Pavement temperature > 50 °C: definitely modified - Special application (bridge deck, airport): definitely modified - Life-cycle cost analysis showing positive NPV 3. Modified bitumen selection — grade per IS 15462 / IS 15469 by climate and traffic. 4. Mix design (IRC:111:2009): - Higher binder content (vs conventional) - Verify Marshall, ITSR, rutting, fatigue - Trial mix with project materials 5. Procurement: - Modified bitumen per IS 15462:2018 / IS 15469 - Source qualification: NABL test report from manufacturer - Local supplier preferred (avoid cooling and separation in long transport) 6. Plant + transport: - Maintain temperature 160-170 °C in storage tank (heated, agitated) - Heated transport tanker, journey time < 60 min 7. Lay-down (IRC:111:2009): - Slightly higher temperature than conventional (155-165 °C discharge; 145-155 °C lay-down) - Avoid prolonged storage in lay-down hopper 8. Compaction — same procedures as conventional; achieve density ≥ 92-94 % TMD. 9. Quality acceptance: - Per-tanker softening point, penetration, elastic recovery test - Per-day mix design verification - Per-section density and surface tolerance 10. Performance monitoring — IRI, rutting, cracking at 6 mo, 1 yr, 2 yr, 5 yr.

Modified bitumen has matured as a routine component of high-traffic Indian pavements; NHAI's NHDP and Bharatmala corridors use PMB or CRMB on most BC layers.