Materials Ground
Portland clinker is the main constituent of most cements. In Portland cement, a little calcium sulfate (typically 3-10%) is added in order to retard the hydration of tricalcium aluminate. The calcium sulfate may consist of natural gypsum, anhydrite, or synthetic wastes such as flue-gas desulfurization gypsum. In addition, up to 5% calcium carbonate and up to 1% of other minerals may be added. It is normal to add a certain amount of water, and small quantities of organic grinding aids and performance enhancers. "Blended cements" and Masonry cements may include large additions (up to 40%) of natural pozzolans, fly ash, limestone, silica fume or metakaolin. Blastfurnace slag cement may include up to 70% ground granulated blast furnace slag. See cement. Gypsum and calcium carbonate are relatively soft minerals, and rapidly grind to ultra-fine particles. Grinding aids are typically chemicals added at a rate of 0.01-0.03% that coat the newly formed surfaces of broken mineral particles and prevent re-agglomeration. They include 1,2-propanediol, acetic acid, triethanolamine and lignosulfonates.
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