Blastfurnace Cement is a special blend of two components; ground granulated blastfurnace slag (GGBS) and portland cement (OPC). GGBS is a by-product of the iron-making process in a blastfurnace. It is produced by the rapid water-quenching of the molten slag under controlled conditions. This granulation process yields sand-sized particles of highly glassy material of high reactivity. The granulated slag is then dried and milled to produce GGBS of cement fineness.
Although there are similarities in the intrinsic chemical and physical properties between GGBS and OPC by virtues of similar raw materials, burning temperature and fineness, the rapid quenching process in slag production yields oxide compounds are different. They also hydrates differently.
Hence, unlike OPC, GGBS is not computed into the 4 major compounds or ‘phases’ i.e. in % C2S, C3S, C3A and C4AF.
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