Limestone powder

Fine limestone has been added to Portland cement for decades. This is normally achieved by “intergrinding” it with Portland cement clinker in the cement mill. Under normal operating conditions this will result in a surface area of the limestone fraction of between 800 and 1100 m2/kg (depending on the grindability of the limestone) for a surface area of the clinker fraction of in the region of 400 m2/kg. Less often the limestone is ground separately and blended with Portland cement. Separate addition of limestone to concrete as a clinker replacement is not widely practiced in conventional concrete, but is used as filler for modifying the rheology of self-compacting concrete.

In the early literature limestone was generally regarded as “inert filler”. For this reason it has e.g. become the main constituent in most masonry cements where high levels of replacement of the Portland cement are needed to reproduce the properties of traditional lime mortars. However, for its application in concrete, which is the primary focus of this report, the limestone’s contribution to the hydration reactions can be significant when it is co-ground with the clinker, albeit in relatively small amounts. So much so that it can arguably be classified as an SCM alongside GBFS and fly ash.

The first significant use of limestone in general purpose Portland cement took place during WWII when it was used in several European countries to cut costs and increase output (Lea, 1970). Its widespread use today can be traced back to the 1973 oil crisis, with France, which had low production of fly ash and blast furnace slag, leading the way. The Portland limestone cements in the European cement standard EN 197-1 (2001), were adopted more or less un-changed from the French standard NF P 15-301 (1981).

A systematic review of all standards and specifications for limestone and Portland limestone cements is beyond the scope of this report.