Investigations of a Ground Granulated Blast Furnace Slag Containing Merwinitic Crystallization


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Title: Investigations of a Ground Granulated Blast Furnace Slag Containing Merwinitic Crystallization

Author(s): John P. H. Frearson and J. M. Uren

Publication: Special Publication

Volume: 91


Appears on pages(s): 1401-1422

Keywords: alkali-aggregate reactions; blast furnace slag; blended cements; chemical analysis; crystallization; expansion; glass content; sulfate resistance.

Date: 2/1/1986

A second source of ground granulated blast-furnace slag ('slag') has become available in the UK, from Purfleet in South East England. The Purfleet slag has a slightly higher lime-silica ratio (c/s) and calcium content than the initial source at Scunthorpe. The slag has a potentially higher rate of hydration because of its chemical composition, but as a consequence can contain up to 30% by volume of merwinite crystallites included within its glass structure. The presence of these crystallites has been found to increase further the reactivity of the slag glass. Scanning election microscope (SEM) studies of concrete containing the slag have confirmed that the glassy particles containing merwinitic crystallites are more reactive than pure glass particles, also that an adequate supply of unreacted glass remains even in mature concrete. Testing of this merwinitic slag has shown no factors disadvantageous to slag reaction or performance and has confirmed that, when blended in appropriate proportions with Portland cement, it can for example, increase sulphate resistance and reduce expansion due to alkali-silica reaction. The results of the investigations reported are supported by a brief review of published literature which confirms that slag performance cannot be directly related to absolute glass content.