GGBS (Ground Granulated Blast-furnace Slag)

Ground Granulated Blast-furnace Slag (GGBS) is a cementitious by-product of iron production. Liquid slag from blast furnaces (containing calcium silicates and aluminates) is rapidly water-quenched, producing glassy granules that are then ground to cement-fineness. Used as a partial replacement for OPC clinker in concrete (typically 25-70%), GGBS provides cementitious properties when activated by the alkalinity of OPC. The Indian Standard IS 16714:2018 governs GGBS specifications; IS 12089 covers slag use in cement.

GGBS reactions: when ground GGBS contacts water in concrete, it slowly dissolves, releasing calcium and silicate ions that combine with calcium hydroxide (a by-product of OPC hydration) to form additional calcium silicate hydrates. This 'pozzolanic-style' reaction is slower than OPC hydration, contributing to the slower early-strength but better long-term strength of GGBS-bearing concrete. GGBS also produces a denser microstructure than OPC alone, with smaller capillary pores and lower permeability — translating to better durability against chloride, sulphate, and freeze-thaw.

Indian use of GGBS: (1) Partial replacement of OPC in cement production — Portland Slag Cement (PSC) per IS 455 contains 25-70% GGBS. (2) Direct addition to RMC at the plant for special concretes — high-performance, marine, or sulphate-resistant. (3) Mass concrete with low heat of hydration. Major Indian GGBS suppliers: Tata Steel (Jamshedpur), JSPL (Raigarh), JSW (Vidi/Bellary), SAIL (Bokaro/Bhilai/Burnpur). The carbon footprint of GGBS is roughly 1/15 of OPC clinker — making GGBS a significant lever for lowering concrete's embodied CO2. Modern sustainable construction in India increasingly specifies 30-50% GGBS replacement in mass concrete and high-durability applications, justified by both cost savings and lower environmental impact.