IS 6909 : 1990Super Sulphated Cement - Specification

IS 6909:1990 is the specification for Super-Sulphated Cement (SSC) — a slag-based cement (a high proportion of granulated blast-furnace slag activated by calcium sulphate with a little clinker/lime) made for highly aggressive sulphate and chemically-hostile environments: marine works, sulphate-bearing ground, sewage/effluent and some industrial exposures, and as a low-heat binder for mass concrete.

It sits in the special-cement family:

• IS 12330 — Sulphate-Resisting Portland Cement (the C₃A-limited alternative) · IS 455 — Portland Slag Cement
• IS 12089 granulated slag (the principal raw material) · IS 456 — concrete (exposure classes) · IS 12600 — low-heat cement

SSC's binding system is slag-dominated (very low Portland clinker), which gives it strong chemical resistance but also a distinct, demanding behaviour:

• Excellent sulphate / chemical resistance & low heat of hydration — the slag system has very little of the C₃A and free lime that sulphates and acids attack, so it outperforms even SRPC in severe sulphate exposure and suits mass concrete
• Slow early strength; very curing- and temperature-sensitive — like all slag-rich binders it gains strength slowly and needs prolonged, careful moist curing; it is sensitive to hot/dry conditions and to high water content
• Storage-sensitive — more prone to deterioration in storage than OPC; use fresh

The engineering point: SSC is a *specialist* binder chosen for severe chemical/sulphate exposure and low heat, but it punishes poor curing and bad handling more than OPC — its durability advantage is only realised with the disciplined curing, mix and storage its slag chemistry demands. It is not a drop-in OPC substitute.

Scenario: a structure in highly sulphate-aggressive ground / sewage exposure where even SRPC is marginal.

Step 1 — classify exposure: quantify the sulphate/chemical severity (IS 456); for very severe sulphate, SSC (IS 6909) or slag cement over plain SRPC.

Step 2 — design dense, to later age: low W/C, IS 10262 mix to the specified later age (slow early strength is expected).

Step 3 — curing is critical: extended, careful moist curing — SSC is acutely curing- and temperature-sensitive; under-curing forfeits the chemical resistance.

Step 4 — fresh cement & control: use fresh SSC (storage-sensitive); control placing in hot/dry conditions.

Step 5 — accept at proper age per IS 456.

With disciplined curing and a dense low-permeability mix, SSC gives outstanding sulphate/chemical durability and low heat; mishandled (short curing, hot placing, stale cement) it under-performs badly — the failure mode of all slag-rich binders, amplified.

1. Treating SSC like OPC. It is slag-dominated — slow early strength, acute curing/temperature sensitivity; an OPC schedule fails it.

2. Under-curing. The single biggest error — SSC's chemical resistance depends on prolonged careful moist curing far more than OPC.

3. Using stale/poorly-stored cement. SSC deteriorates in storage more readily than OPC — use fresh.

4. Ignoring its niche. It is for severe sulphate/chemical exposure and low heat — not a general-purpose cement.

5. Permeable concrete. As with all chemical-resistance cements, low W/C and good compaction are co-requisites — chemistry plus low permeability.

• IS 12330 — SRPC (the C₃A-limited alternative) · IS 455 — Portland Slag Cement
• IS 12089 — granulated slag (SSC's principal raw material) · IS 456 — exposure/durability
• IS 12600 — low-heat cement (SSC is also low-heat) · IS 10262 — mix design
• IS 3085 — permeability · IS 4031 Part 1 — physical tests

IS 6909 is reaffirmed and a niche but important binder: super-sulphated cement is one of the most chemically resistant cements available — for very severe sulphate, effluent and aggressive-chemical exposure it can outperform SRPC — and it is inherently low-heat. The catch, and the reason it is under-used, is that it is unforgiving: slag-dominated chemistry means slow early strength and an acute dependence on prolonged, careful curing, freshness and controlled placing temperature. Specified for its niche and handled with slag-binder discipline (design to later age, cure long and well, use fresh cement, build dense concrete) it delivers exceptional chemical durability; treated as a general OPC with a casual curing regime it disappoints comprehensively. Match it to severe chemical exposure, and commit to the curing it demands.