Portland Slag Cement – Specification
1989 Edition

IS 455:1989 sets maximum limits for chemical components in Portland Slag Cement as follows: Magnesium oxide (MgO) up to 10.0%, Sulphur trioxide (SO₃) up to 3.0%, Sulphide sulphur (S) up to 1.5%, Loss on ignition not exceeding 5.0%, and Insoluble residue capped at 4.0%. Additionally, chloride content must not exceed 0.05% for prestressed and long-span reinforced concrete, while other concrete types have limits as agreed. Granulated slag used must meet IS 12089:1987 standards, with slag content ranging between 25% and 65% by mass. These specifications ensure the cement’s durability and performance.

Per IS 455, compressive strength tests for Portland slag cement are conducted on mortar cubes prepared according to IS 4031 (Part 6). Mortar cubes, typically 70.6 mm in size, are made using standard sand and a specified water-cement ratio, then cured under controlled conditions for intervals of 3, 7, and 28 days. The strength is measured using a calibrated compression testing machine, with the cement required to exhibit a consistent increase in strength beyond 72 hours. Typical strength ranges are approximately 16-18 MPa at 3 days, 22-25 MPa at 7 days, and 33-40 MPa at 28 days, ensuring compliance with durability and performance criteria.

According to IS 455 Clause 4.1, Portland slag cement must contain granulated slag within the range of 25% to 65% by weight of the total cementitious material. The cement is produced either by intimately intergrinding Portland cement clinker, granulated slag, and gypsum, or by uniformly blending finely ground granulated slag with Portland cement. Additives are limited to natural or chemical gypsum, water, and up to 1% air-entraining agents. Additionally, the cement must comply with chemical limits such as sulfur trioxide not exceeding 3.0%, ensuring both chemical and physical standards for optimal performance.

IS 455 mandates that cement bags typically have a net mass of 50 kg, though 25 kg bags are acceptable if mutually agreed. The tolerance criteria specify that no more than 5% of bags in a sample can have a minus deviation exceeding 2% of the declared net mass, and no individual bag should be below 4% less than the nominal weight. The average net mass of the sampled bags must be at least equal to the specified weight. Packaging materials must be agreed upon between manufacturer and purchaser, conforming to regulatory standards to ensure accurate and fair packaging.

IS 455 enhances the resistance of Portland Slag Cement to sulfate and acidic conditions through stringent chemical and physical criteria. Chemically, it limits magnesium oxide to 8.0%, sulphur trioxide to 3.0%, sulphide sulphur to 1.5%, loss on ignition to 5.0%, and insoluble residue to 4.0%, thereby reducing susceptibility to harmful reactions like sulfate attack. Physically, expansion tests such as Le-Chatelier expansion must not exceed 10 mm, and autoclave expansion is capped at 0.8%, indicating good dimensional stability. Together, these requirements ensure the cement’s durability in aggressive environments.