Limestone fines to BS 7979, Specification for limestone fines for use with Portland cement is a fine powder obtained from the processing of limestone.
Limestone fines can be added to Portland cement as an addition, either at the factory to create a composite cement or at the batch plant to form a combination cement.
There is uncertainty over whether limestone fines should be classified as a Type I (nearly inert as a filler aggregate) or Type II addition (with pozzolanic or latent hydraulic properties, for example, materials like fly ash (fa) and ground granulated blastfurnace slag (ggbs)). Limestone is less reactive than either fa or ggbs, but research shows that it can have slight reactivity as well as beneficial physical effects conferred by virtue of its fine particle size.
BS 8500, Concrete - Complementary British Standard to BS EN 206 permits the use of limestone fines, under broad designation IIA (6-20% proportion of Portland cement), in a way that makes it unnecessary to resolve whether it is a Type I or II addition.