Limestone consists mainly of CaCO3 with some clay content and organic matter. Limestone is not a pozzolan; therefore it creates no C-S-H during hydration. However, limestone particles that have a nominal diameter of less than 0.1mm promote hydration by providing nucleation sites for the reaction products.


ASTM Committee C-1 allows a maximum of 5% limestone interground with the clinker in the production of portland cement.


The following advantages are realized as a result of integrating limestone with clinker in the production of portland cement:


The limestone used in portland cement should be of at least 75% calcium carbonate by mass, and the organic matter is limited to 0.2% by mass (CEN, 1992). The optimum amount of portland cement replacement with limestone is dependent upon the composition of the clinker with respect to C3A content (Detwiler et al., 1996). When using this or any other alternative cementing material with portland cement, it is necessary to create trial mixtures to ensure proper proportioning for the desired properties.