IRC SP 98 : 2013Guidelines for the Use of Waste Plastic in Hot Bituminous Mixes

IRC SP 98 specifies guidelines for the use of waste plastic in hot bituminous mixes for flexible pavement construction. It allows construction of pavements that incorporate shredded post-consumer plastic waste (LDPE / HDPE / PP carry bags, single-use packaging) as a partial bitumen modifier, simultaneously addressing road performance and plastic waste disposal.

Use IRC SP 98 when: - Specifying flexible pavement (BC, DBM) where waste-plastic incorporation is mandated by state policy or sustainability objectives - MoRTH / NHAI / state PWD contracts that specify 'plastic-modified bitumen' (PMB) or 'plastic waste mix' - Urban road projects targeting Swachh Bharat Mission / smart city sustainability metrics - Environmental compliance for projects in cities with mandated plastic-waste utilisation rules (Maharashtra, Karnataka, TN, Rajasthan have such mandates)

This is a *guideline* (SP series — Special Publication), not a binding specification. The MoRTH Specifications for Road and Bridge Works (5th Revision) cite IRC SP 98 as the recommended practice when waste plastic is added to bituminous mixes.

The dry process (mixing shredded plastic with hot aggregate before adding bitumen) is the standard method covered by IRC SP 98. The wet process (pre-blending plastic with bitumen at refinery) is a different chemistry — covered by IS 15462 and IRC SP 53 for polymer-modified bitumen.

Sequence at the asphalt plant: 1. Aggregate heated to 165-170 °C in the dryer drum (slightly higher than conventional 155-160 °C to compensate for plastic heat sink) 2. Shredded waste plastic (size 2-4 mm, dry, contaminant-free) added to the hot aggregate at 8 % by mass of bitumen content (typically 0.4-0.5 % by mass of total mix) 3. Brief mixing (~30 seconds) — plastic melts onto aggregate surface, forming a thin coating 4. Heated bitumen (VG-30 or VG-40 per IS 73:2013) added at design dose 5. Standard mixing duration; mix discharged at 150-160 °C (slightly higher than conventional) 6. Transport, lay-down, compaction proceed as conventional bituminous mix

What plastic does in the mix: - Coats aggregate surface — improves bitumen-aggregate adhesion (reduces moisture-induced stripping) - Improves softening point of binder — better resistance to rutting at high pavement temperature - Improves Marshall stability by 10-25 % - Improves resistance to fatigue cracking by 20-40 % - Reduces overall bitumen consumption by ~5-8 % (the plastic substitutes some of the binder)

Plastic acceptance criteria (Clause 5): - Type: LDPE, HDPE, PP, PET — non-PVC (PVC releases HCl on heating, banned) - Size: 2-4 mm shred (sieve through 4.75 mm, retained on 600 µm) - Cleanliness: free of food residue, dirt, metal contaminants; moisture < 1 % - Source: post-consumer waste from segregated MSW collection or commercial recycling - Storage: dry, covered, separate from other materials

Plastic dose: - 8 % by mass of bitumen (typical, IRC SP 98 Clause 6) - Range: 6-10 % depending on aggregate gradation and target performance - Above 10 %, mix becomes harder to work — risk of segregation, poor compaction

Bitumen reduction: - Mix design optimum bitumen content reduced by 0.3-0.5 % vs conventional control - Typical: VG-30 or VG-40 at 4.8-5.2 % (vs 5.0-5.5 % conventional)

Plant temperature: - Aggregate heating: 165-170 °C - Mixed-mix discharge: 155-165 °C - Lay-down: 145-150 °C - Compaction: complete by 110 °C (slightly faster cooling than conventional)

Marshall test results (typical for VG-30 + 8 % plastic): - Stability: ≥ 13 kN (vs 9-11 kN conventional) - Flow: 2-4 mm - Air voids: 3-5 % - VFB: 65-75 %

Performance limits (vs IRC:111 conventional mix): - Indirect tensile strength ratio (ITSR, freeze-thaw): ≥ 80 % (vs 70 % conventional minimum) - Rutting (Hamburg wheel-tracker, 50 °C, 20,000 passes): ≤ 8 mm - Fatigue life (IDT fatigue, 50 µstrain): ≥ 200,000 cycles

Plastic supply: - Typical urban project: 1-3 t plastic per km of single lane BC - Sourced from MSW recycling units, plastic processing waste, or specialised SP-98-compliant suppliers

• IRC:37:2018 — design of flexible pavements (the parent design code).
• IRC:111:2009 — specifications for dense-graded bituminous mixes (BC, DBM mix design).
• IRC SP 53:2010 — guidelines on use of modified bitumen (the wet-process counterpart).
• IS 73:2013 — paving bitumen (the bitumen base material).
• IS 15462:2018 — polymer-modified bitumen (PMB) specification.
• IS 15469 — crumb rubber modified bitumen (CRMB) — alternative sustainable additive.
• IS 383:2016 — coarse and fine aggregates for concrete (and bitumen mixes).
• MoRTH Specifications for Road and Bridge Works (5th Revision) — overall contract specification.
• Plastic Waste Management Rules 2016 (MoEFCC) — statutory framework that incentivises plastic-road construction.
• Swachh Bharat Mission guidelines — urban policy alignment.
• IRC Special Publication 100 series — broader sustainability and quality guidelines for road construction.

1. PVC contamination in plastic feedstock. PVC releases HCl gas at mixing temperature, corrodes plant, hazardous to operators. Source feedstock must be PVC-free; verify by chlorine spot test (Beilstein test). 2. Wet plastic feedstock. Moisture in plastic causes steam during mixing, foaming, poor coating. Drying is mandatory; moisture < 1 % at point of use. 3. Plastic shred size too large or too small. > 4 mm: doesn't melt fully on aggregate, lumps in mix. < 600 µm: hard to handle, dust hazard, escapes via plant exhaust. Stick to 2-4 mm range. 4. Mixing at conventional temperature. Below 165 °C aggregate temperature, plastic doesn't fully melt and coat. Boost dryer temperature ~5-10 °C above conventional. 5. No reduction of bitumen dose. If you maintain conventional bitumen content while adding plastic, the mix becomes too rich (binder excess), causes flushing in summer. 6. Overdosing beyond 10 % plastic. Mix becomes too stiff, hard to compact, prone to segregation. Stay within IRC SP 98 dose range. 7. Single-source plastic without consistency check. Plastic chemistry varies by feedstock; LDPE behaves differently than PP. Test mix design with the actual plastic source; don't extrapolate from supplier brochures. 8. Plant operator unfamiliar with the process. The dry process needs a brief operator training; it's not a drop-in replacement for conventional mix. 9. No quality check on plastic supply. Demand a supplier certificate per batch: type (LDPE/HDPE/PP), size, moisture, contamination, source. 10. Using modified-bitumen design parameters when waste-plastic is dry-processed. The two are different; SP 98 has its own mix design protocol distinct from IRC SP 53 PMB.

Standard flexible pavement design + construction with waste plastic:

1. Pavement design (IRC:37:2018) — traffic, subgrade CBR → layer thicknesses (subgrade → GSB → WMM → DBM → BC). 2. Material selection — VG-30 / VG-40 bitumen (IS 73), aggregate per MoRTH 500, plus 8 % waste plastic per IRC SP 98. 3. Mix design (IRC:111:2009) modified for waste plastic: - Marshall mix design with plastic added during aggregate heating - Optimum bitumen content reduced by 0.3-0.5 % - Verify ITSR ≥ 80 %, rutting ≤ 8 mm, fatigue ≥ 200,000 cycles 4. Procurement: - Bitumen per IS 73:2013 - Aggregate per MoRTH / IS 383 - Plastic per IRC SP 98 supply spec (dry, shredded 2-4 mm, PVC-free, source-certified) 5. Plant calibration — dryer temperature ~5 °C higher; plastic feeder calibration; mixing time adjustment 6. Lay-down — paver at 145-150 °C (slightly higher than conventional) 7. Compaction — same as conventional; complete by 110 °C 8. Quality acceptance: - Density ≥ 92-94 % TMD (per MoRTH) - Marshall stability + flow per mix design - Random core extraction for in-situ DFT and binder content verification 9. Documentation: - Plastic supply certificates per consignment - Per-day mix design verification - Per-section density logs 10. Performance monitoring — at 6 months and 1 year for rutting, cracking, IRI, raveling

IRC SP 98 enters at step 2 (material selection), drives steps 3-9 (mix design through QA), and is most often quoted in environmental/sustainability sections of MoRTH project specifications.