The role of calcium carbonate in cement hydration

Thomas Matschei, B. Lothenbach, F. P. Glasser

Research output: Contribution to journalArticle

340 Citations (Scopus)

Abstract

Limestone, mainly consisting of calcite, is a permitted additive to Portland cements often up to a 5 wt.% limit. It is shown by experiment and calculation that much, if not all, of this calcite is reactive and affects the distribution of lime, alumina and sulfate and thereby alters the mineralogy of hydrated cement pastes. Calcite affects the mineralogical variant of the AFm phase(s). Calcite additions affect the amount of free calcium hydroxide as well as the balance between AFm and AFt phases, although C-S-H is unaffected in much of the range of compositions. Generic data are shown in graphical form to quantify these mineralogical changes as functions of cement composition and amount of added calcite. Calculations of the specific volume of solids as a function of calcite addition suggest that the space-filling ability of the paste is optimised when the calcite content is adjusted to maximise the AFt content. However, before the calculated data can be used uncritically, certain kinetic constraints on reactivity also need to be assessed. Progress towards the quantification of paste mineralogy suggests that (i) elucidation of the mineralogy of pastes, particularly blended cement pastes, is facilitated by using both theoretical and experimental approaches and (ii) that the ultimate goal, of calculating paste mineralogy from the bulk chemistry, is attainable. (c) 2006 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)551-558
Number of pages8
JournalCement and Concrete Research
Volume37
Issue number4
DOIs
Publication statusPublished - Apr 2007

Keywords

  • cement paste mineralogy
  • AFm
  • AFt
  • calcium carbonate
  • phase relations
  • thermodynamics
  • Portland-limestone cements
  • concrete

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