Portland Slag Cement (PSC)

Portland Slag Cement (PSC) is hydraulic cement made by grinding Ordinary Portland Cement (OPC) clinker with 25-70% Ground Granulated Blast-furnace Slag (GGBS) — a by-product of iron production. The Indian Standard IS 455:2015 governs PSC specifications. GGBS is a latent hydraulic material — it has cementitious properties but reacts only when activated by the alkalinity of OPC clinker. The combined product has properties intermediate between pure OPC and pure GGBS, with the proportion of slag adjustable to match application needs.

Indian PSC manufacturers: Ultratech (in select grades), ACC, Ambuja, Tata Steel (especially), JSW, Shree Cement. The market is smaller than PPC because GGBS supply is limited to regions near steel plants; coastal western India (Visakhapatnam, Mumbai, Goa) and eastern India (Kolkata, Bhilai) have significant PSC use. PSC's principal advantages: (a) Better resistance to chloride and sulphate attack — GGBS particles are denser and create a less-permeable concrete microstructure; (b) Lower heat of hydration — useful for mass concrete in dams and large rafts; (c) Better long-term strength gain — PSC at 56 days can exceed OPC at 28 days; (d) Reduced embodied carbon — slag replacement saves 30-50% CO2 vs pure OPC.

Drawbacks: (a) Slower early strength — 7-day strength is typically 50-55% of 28-day (similar to PPC); (b) Longer curing required — minimum 10 days per IS 456 Cl. 13.5 vs 7 for OPC; (c) Limited regional availability; (d) Slightly more sensitive to admixture compatibility — PSC + PCE superplasticisers require trial mixes for optimal compatibility. Like PPC, PSC must be used with extended curing in hot weather or aggressive environments. Modern Indian mass-concrete construction increasingly uses PSC for dams and major bridges (Bandra-Worli Sea Link, Mumbai Trans-Harbour Link) where the durability advantages over OPC justify the longer construction cycle.