IS 455 : 2015Portland Slag Cement - Specification

IS 455 specifies Portland Slag Cement (PSC) — Portland cement clinker blended with Granulated Blast-Furnace Slag (GGBS) from steel manufacture. PSC is one of three major blended-cement options in Indian construction (alongside PPC fly-ash IS 1489 Part 1 and PPC calcined-clay IS 1489 Part 2).

Use PSC when: - General construction where PSC is locally available + competitive - Mass concrete / dam construction (lower heat of hydration than OPC) - Marine / coastal exposure (better chloride resistance than OPC) - Sulphate-rich soil (good sulphate resistance with high slag content) - Sustainability targets (lower carbon than OPC; uses industrial by-product) - Long-term durability projects (PSC gains strength longer; better long-term)

PSC vs alternatives:

| Cement | Pozzolan source | Heat (mass conc) | Strength curve | Cost | |---|---|---|---|---| | OPC (IS 8112 / IS 12269) | None | High | Fast early, plateaus | Highest | | PPC fly-ash (IS 1489 Part 1) | Coal fly ash | Medium | Slower early, gains long | Similar / lower | | PSC (IS 455 — this code) | GGBS from steel | Lowest | Slow early, gains very long | Similar / lower | | PPC calcined clay (IS 1489 Part 2) | Calcined clay | Medium | Gradual; sustainable | Higher | | SRC (IS 12330) | None (low C₃A clinker) | Medium | Standard; sulphate-resistant | Higher |

Composition (Clause 5): - Portland clinker: 35-65 % - GGBS: 35-65 % - Gypsum: 3-7 % (set regulator)

High-slag PSC (>50 % GGBS) is essentially equivalent to European CEM III/B: high durability, low heat, but slow early strength.

Acceptance criteria (per IS 455:2015):

| Property | Acceptance | |---|---| | 3-day strength (mortar cube) | ≥ 16 N/mm² | | 7-day strength | ≥ 22 N/mm² | | 28-day strength | ≥ 33 N/mm² | | 28-day at 50%+ slag (Class A) | ≥ 33 N/mm² | | Fineness (Blaine) | ≥ 225 m²/kg | | Setting time: initial | ≥ 30 minutes | | Setting time: final | ≤ 600 minutes | | Soundness: Le Chatelier | ≤ 10 mm | | Soundness: autoclave | ≤ 0.8 % | | LOI (max) | 4.0 % | | MgO (max) | 6.0 % | | SO₃ (max) | 3.0 % | | Cl⁻ (max) | 0.10 % | | Insoluble residue (max) | per spec |

Long-term strength gain: - 28-day: ~33 MPa (similar to OPC 33 grade) - 90-day: ~40-45 MPa (gain due to slag pozzolanic reaction) - 1-year: ~45-50 MPa (continued gain) - Compared to OPC: similar / slightly higher long-term, slower early

Heat of hydration: - 7-day: 230-270 kJ/kg (vs OPC at 280-320) - Lower thermal cracking risk in mass concrete (raft, dam, large foundation)

Mix design implications: - W/c: similar to OPC for given workability - Cement content: similar (PSC + OPC mix designs largely interchangeable for similar w/c) - Curing: longer recommended (14-28 days minimum) for full strength + durability development

Cost (typical 2026): - PSC: ₹400-450 per 50 kg bag (similar to OPC; sometimes 5-10 % cheaper) - Available regionally where steel mills + GGBS supply exist (Vizag, Kolkata, Tamil Nadu, Gujarat) - Limited availability outside steel-belt regions

Carbon footprint: - PSC: 500-700 kg CO₂/t (vs OPC at 850-900) - Lower clinker content + use of waste GGBS = significant carbon savings

• IS 12269:2013 — OPC 53 grade.
• IS 8112:1989 — OPC 43 grade.
• IS 269:2015 — consolidated OPC.
• IS 1489 Part 1:2015 — PPC fly-ash (alternative blended cement).
• IS 1489 Part 2:2015 — PPC calcined-clay.
• IS 12330:1988 — Sulphate-Resisting Cement.
• IS 4031 series — physical tests.
• IS 4032:1985 — chemical analysis.
• IS 456:2000 — RCC code.
• IS 10262:2019 — concrete mix design.
• IS 9103:1999 — admixtures.
• IS 12089 — granulated slag for cement.
• ASTM C595 — international counterpart for blended cements.
• BS EN 197-1 (CEM III) — European slag cement standard.
• Japanese JIS R 5211 — Portland blast-furnace slag cement.

1. PSC in fast-cycle precast. Slower early strength; mould rotation slowed. Use OPC 43/53 OR RHPC (IS 8041:1990). 2. Inadequate cure. PSC's pozzolanic reaction continues; without good cure, long-term strength + durability lost. 14-28 day moist cure recommended. 3. No project-specific trial mix. PSC behaves differently than OPC; same w/c may give different workability + strength. Trial verify. 4. Confused with PPC. PSC = slag-based; PPC = fly-ash or calcined-clay. Different products; different properties. Specify clearly. 5. Old / damp PSC stored. Loses reactivity; weak concrete. Use within 3 months. 6. Specifying PSC where SRC is required. PSC has good but not maximum sulphate resistance. For very aggressive sulphate exposure, SRC (IS 12330) preferred. 7. Hot weather + PSC + retarder. Setting may be excessively delayed. Balance retarder dose. 8. No supplier qualification audit. GGBS source variation affects PSC quality. Verify with IS 4031 series acceptance. 9. Mass concrete pour without PSC heat advantage utilised. PSC is naturally low-heat; can pour thicker sections without thermal issues. Design accordingly. 10. Carbon savings claim without third-party verification. For green building rating, demand EPD (Environmental Product Declaration) from supplier.

Indian cement market (2026): - OPC variants: 30-40 % market share - PPC fly-ash: 50-60 % market share (dominant in many regions) - PSC: 5-10 % market share (regional; steel-belt areas) - Composite cement: emerging

PSC adoption trends: - Growing in Vizag, Kolkata, Tamil Nadu (proximity to steel mills) - Limited outside steel-belt due to GGBS supply constraints - Sustainability + carbon reduction driving more demand - LC3 + composite blends emerging as next-generation blended cements

Project workflow with PSC:

1. Local availability check — verify PSC supply within reasonable distance. 2. Mix design (IS 10262:2019) — trial mix with project materials. 3. Trial mix verification — strength at 7d, 28d, 90d (long-term). 4. Curing planning — extended cure (14-28 days) accommodated in schedule. 5. Procurement — ISI marked PSC. 6. Construction — slower early strength may affect formwork removal schedule. 7. Quality acceptance — strength + durability tests per IS 456. 8. Long-term performance — verify chloride / sulphate resistance via IS 9013:1978 water permeability or RCPT.

PSC is an excellent cement for mass concrete + marine + sulphate exposure + sustainability projects. Limited regional availability remains the main constraint vs PPC fly-ash.