Limestone as MAC
The addition of small amounts of limestone in Portland cement has been practiced since the early 1980s. The inclusion of limestone as a minor additional constituent (MAC) offers economic and technical benefits to the cement producer. However, despite its wide acceptance, some debate remains over the effects of limestone on the concrete ultimately produced by the cement.
Since the early 1980s it has been permitted in Canadian Standards to include up to five per cent of limestone in Portland cement (CSA A5-M77 – 1980). Since that time this addition has been more widely accepted across the world, including in European, Australian, South African and, most recently, in US cement standards. The advantages of this were seen in both economic and technical terms, but the actual effects of limestone inclusion have been, and still are, a subject of debate.