Reference card — verified IS codes
Verified 2026-09-14 against ~/Standards library + BIS portal. ConcreteInfo reference card.
Codes referenced
Sixth Revision consolidated OPC 33 and 43 grades under one standard; covers all three grades with grade-specific strength requirements. Earlier code splits (IS 8112 for 43, IS 12269 for 53) are legacy references.
Pt 1 fly ash based; Pt 2 calcined clay based. Both require 33 MPa minimum 28-day strength; slower strength gain, better durability.
GGBS 25-70% by mass; 33 MPa minimum 28-day strength. Lower permeability, resists alkali-silica reaction.
Cl 5.2 admits mineral admixtures as part replacement of cement and states no percentage of its own. Cl 5.2.1.1 allows fly ash conforming to IS 3812 (Part 1) with uniform blending. The dosage bands come from IS 10262:2019 Table 9 — fly ash 15–30%, GGBS 25–50%, metakaolin 5–15%, silica fume 5–10% by mass of total cementitious materials — and, for what may be counted toward cement content, from IS 456 Table 5 Note 1, which points to IS 1489 (Part 1) for pozzolana and IS 455 for slag. LC3 has no dedicated IS code; references IS 1489 (Pt 2) and IS 3812.
OPC 43 vs OPC 53 — when each, cost premium
OPC 53 (IS 269:2015, 53 grade) is the high-strength grade most Indian RMC plants default to. The headline difference is 28-day strength (53 vs 43 MPa), but the practical difference is the required w/c ratio for the same target strength: OPC 53 lets you hit M40 with w/c ~0.40 where OPC 43 needs ~0.36 with the same aggregates, which means higher cement content and more heat of hydration. Cost-wise OPC 53 carries an 8-12% premium per bag over OPC 43 — a real consideration for slab-on-grade and mass pours where the 53 MPa strength is wasted.
High-rise columns & shear walls, precast elements, post-tensioned slabs, M40+ structural concrete, early stripping cycles (7-day strength matters).
Mass foundations, slab-on-grade, plaster / non-structural concrete, M25 and below. Saves cost without sacrificing durability.
Thin sections with high heat-of-hydration risk (large pours in summer), and where trial mix hasn't validated the higher strength gain.
PPC (IS 1489 Part 1) — fly ash, durability, lower heat
PPC blends 15–35% fly ash with OPC clinker. The pozzolanic reaction between fly ash (SiO₂ + Al₂O₃) and the calcium hydroxide released during cement hydration produces additional C-S-H gel over 28-90 days. The trade-off is well-known: slower strength gain at 7 and 14 days, but equal or higher strength at 90 days, with a ~25% lower heat of hydration and significantly better chloride / sulphate durability. IS 1489 Part 1 sets the fly ash constituent at 15–35% by mass of PPC. IS 456 Cl 5.2 is the clause that admits mineral admixtures as part replacement of cement, and it is read with the project specification; Cl 5.2.1.1 states no percentage of its own, so the dosage numbers come from IS 10262:2019 Table 9 and from the cement standards.
For marine and coastal structures, retaining walls, and foundation slabs in sulphate-rich soils, PPC is the default cement choice in India. The 5-8% cost saving over OPC 53, combined with the durability dividend, makes PPC the workhorse of Indian RMC.
PSC (IS 455 / IS 1489 Part 2) — slag, chloride resistance
PSC replaces 30-50% of clinker with Ground Granulated Blast Furnace Slag (GGBS) — a glassy by-product of iron manufacture. Slag has latent hydraulic activity: it reacts with water and calcium hydroxide independently of fly ash pozzolanic reaction, so PSC gives better early strength than PPC at typical replacement levels while still reducing heat and chloride permeability. IS 455 specifies the chemical and physical requirements; IS 1489 Part 2 is the alternative specification path for slag-blend cements. For severe marine exposure and de-icing salt environments, PSC with ≥ 50% slag is the Indian code-aligned chloride-resistance choice.
LC3 — Limestone Calcined Clay Cement, ~30% lower CO₂
LC3 is a ternary blend: 50% clinker + 30% calcined clay + 15% limestone + 5% gypsum. The calcined clay (metakaolin) is highly reactive and combines with limestone to form carboaluminate phases that contribute to strength — letting you cut clinker content by ~30% with comparable 28-day strength. The result is ~30% lower embodied CO₂ per tonne of cement compared to OPC. BIS notified LC3 in 2020 (IS 1642:1989 notation; new IS for LC3 is in pipeline). Commercial supply in India is currently limited — primarily Dalmia and a few regional producers — so for general construction in 2026 OPC / PPC / PSC remain the default choices.
Acceptance of cement types per exposure condition
IS 456 Cl 5.3 lists the cement types acceptable for each environmental exposure condition (mild / moderate / severe / very severe / extreme). For chloride / sulphate exposure, IS 456 references IS 269, IS 455 and IS 1489 as the permitted cement specifications, with PSC and PPC as the preferred types for severe exposure. Always confirm the cement type with the project specification before placing concrete — substituting a higher-strength cement (e.g. OPC 53) for a lower one (e.g. PPC) without trial mix is a common audit finding.
Source: IS 456:2000 Cl 5.3 — Cement. Read with IS 269 / IS 12269 / IS 455 / IS 1489 / IS 1642 for type-wise chemical and physical requirements.
Worked example — M30 mix with OPC 53 vs PPC
| Parameter | OPC 53 (IS 12269) | PPC (IS 1489 Pt 1) |
|---|---|---|
| Target 28-d strength | 30 MPa (M30) | 30 MPa (M30) |
| w/c ratio (IS 10262 Table 5) | 0.40 | 0.42 |
| Cement content | 350 kg / m³ | 350 kg / m³ (245 kg OPC + 105 kg fly ash) |
| Water content | 140 kg / m³ | 147 kg / m³ |
| 28-d cube strength (typical) | 32 MPa | 30 MPa (catches up by 56 d) |
| 90-d strength | 36 MPa | 38 MPa (pozzolanic crossover) |
| Heat of hydration (relative) | 1.0 (baseline) | ~0.75 |
| Cost per m³ (cement only) | Baseline | ~5-8% lower |
| Verdict | Use for early strength / high-rise | Use for mass pours, durability, cost |
Common deviations seen on Indian sites
Spec calls for OPC 53 for high-rise columns; site engineer "optimises" by switching to PPC. Mix design isn't revalidated, 7-day strength falls below stripping threshold, and the contractor buys time with calcium chloride accelerator — a durability disaster. Always run a trial mix before cement substitution.
Using OPC 53 for plaster / non-structural screed wastes the strength gain — the higher heat also cracks the surface. Specify OPC 43 or PPC for plaster and save 8-12% per bag.
Low-carbon project specs LC3 for sustainability; site team discovers the regional supplier doesn't stock LC3 bags, and the pour waits a week. Verify supply chain and mill test certificates before specifying LC3 — it is still limited in India in 2026.
PPC loses strength with age faster than OPC because fly ash reacts slowly with atmospheric moisture. IS 1489 mandates a 3-month re-test for stored PPC; sites routinely skip it. Always test stored cement before use.
Field-checklist blocks
A short questionnaire, an inspector's checklist, and three worked examples that show how the cement type on the ticket decides the mix, the schedule and the durability of the whole structure.
Questionnaire — ask before the cement is ordered
- Does the cement type match the exposure condition under IS 456 Cl 5.3 — mild, moderate, severe, very severe or extreme?
- Do the SCMs in the blend fall inside the materials IS 456 Cl 5.2 admits, and inside the dosage bands of IS 10262:2019 Table 9 — fly ash 15–30%, GGBS 25–50%, metakaolin 5–15%, silica fume 5–10% by mass of total cementitious materials?
- Is OPC 53 genuinely needed here — high-rise columns and shear walls, precast, post-tensioned slabs, M40 and above, or an early stripping cycle that depends on 7-day strength?
- Has the mix design been revalidated if the cement type is changing, with a trial mix run and separate cubes cast?
- Is the cement for the whole pour coming from one lot, since mixing two types gives erratic setting, differential strength gain and colour variation?
- If PPC is in the mix, has the schedule been rewritten around the slower early strength — stripping times, post-tensioning release, and the 28-day to 90-day crossover?
- For stored PPC, has the 3-month re-test been done per IS 1489 before the bags go into the mixer?
Inspector's checklist — what to verify in the cement store and on the ticket
- Mill test certificate on file for every lot, matched to the delivery.
- Cement type and grade recorded against the mix design on each delivery ticket.
- Storage age checked, with stored PPC re-tested at 3 months before use.
- Bags of different types physically separated in the store, and the dispensing bin dedicated to one type.
- No cement type changed mid-pour, and where a change is unavoidable, a construction joint with each lot tested separately per IS 516.
- Trial mix run and cubed before any substitution is adopted on site.
- 7-day results checked against the stripping and transfer schedule, not only against the 28-day target.
What happens if… three worked examples
What happens. Both hold 350 kg/m³ of binder. OPC 53 sits at w/c 0.40 with 140 kg/m³ of water; PPC sits at 0.42 with 147 kg/m³, the binder split 245 kg OPC and 105 kg fly ash.
Likely outcome. OPC 53 gives 32 MPa at 28 days and 36 MPa at 90. PPC gives 30 MPa at 28 days, catches up by 56 days and passes it at 90 days with 38 MPa, on about 0.75 of the heat of hydration and 5–8 % less cement cost.
Correction. Use OPC 53 where early strength or a 7-day stripping cycle governs. Use PPC for mass pours and for durability.
What happens. The specification calls for OPC 53, and the site engineer switches to PPC to optimise cost without revalidating the mix design.
Likely outcome. 7-day strength falls below the stripping threshold, and the contractor buys time with a calcium chloride accelerator — a durability problem in a column that will carry the building. The mix design on paper no longer describes the concrete.
Correction. Run a trial mix before any substitution. If the change is adopted, cast separate cubes for each cement lot and rebuild the schedule around the slower early strength.
What happens. PPC loses strength with age faster than OPC, because the fly ash reacts slowly with atmospheric moisture, and the bags go into the mixer without a fresh test.
Likely outcome. The 28-day result lands below target and the cause is not obvious, because the mix design and the plant are both fine. The site ends up chasing a problem that is really a cement-store problem.
Correction. Re-test stored PPC at 3 months per IS 1489, and use it only once the result clears the mix design's target strength.
Frequently Asked Questions
Can PPC and OPC 53 be mixed in the same concrete pour?
What is the strength difference between OPC 53 and PPC at 28 days?
Is LC3 commercially available in India for general construction?
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Amit Haridas
Founder & Proprietor, ConcreteInfo. 25+ years experience in construction QA/QC, concrete technology, RMC plant operations, consulting and technical training across India. For cement-substitution review or mix-design audit, contact amit@concreteinfo.in.
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