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The degree of conversion of highly reactive metakaolin in Portland cement metakaolin paste at different ages as well as the influence of metakaolin on the degree of hydration of Portland cement and composition of C-S-H is investigated by 27Al- and 29Si-MAS NMR spectroscopy. At the age of 7 days, in the paste with 10% of metakaolin, the additive is completely consumed. In the 30% substituted cement paste, the content of metakaolin remains quite high (about 40% of the initial amount) even after 3 months of hydration. At the age of 1 - 3 months, the degree of Portland cement hydration in the presence of metakaolin is of 15% - 20% less than without it, probably, due to deficit of water or spatial restrictions. After 7 days of hydration, about half of C-S-H consists of material derived from metakaolin. Metakaolin mainly contributes to Q2 and Q2 (1Al) species, whereas PC does to Q1. After 1 day of hydration, an amount of ettringite in cement paste with high dosage of metakaolin is higher than in pure PC paste.

Hydration of Portland Cement in the Presence of Highly Reactive Metakaolin