On the Carbonation of Calcium Silicate Compounds

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  • ASANO Shunkichi
    Department of Industrial Chemistry, Faculty of Technology, Kobe University
  • KAMATANI Yukinori
    Department of Industrial Chemistry, Faculty of Technology, Kobe University
  • INOUE Yoshiki
    Department of Industrial Chemistry, Faculty of Technology, Kobe University

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Other Title
  • 「水和セメント構成化合物の炭酸化反応」 (第2報) カルシウム・シリケート化合物の炭酸化反応
  • カルシウム シリケート カゴウブツ ノ タンサンカ ハンノウ

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Abstract

The carbonation of calcium silicate compounds constituting hydrated cement was investigated individually. The samples of xonotlite, tobermorite (2 species), C3S and β-C2S, synthesized from pure chemicals, were carbonated by 100% CO2 gas at gas state (gas reaction), or at wet state of added 100% water (liquid reaction). Reaction rates and the fraction of calcite in CaCO3 were determined by X-ray quantitative analysis. Species and degree of crystallinity of the carbonation products were examined by X-ray diffraction method and infra-red absorption method.<br>The results obtained are as follows:<br>1) The carbonation of hydrated calcium silicates proceeds rapidly, the rate determining process is a surface reaction. The difference of reactivity between xonotlite produced in higher temperature and tobermorite in lower temperature, and in tobermorites of different crystallinity are observed. The reaction products are CaCO3 and silica gel, and CaCO3 is almost crystalline, the morphologic habit is calcite both in gas reaction and in liquid reaction.<br>2) The carbonation of anhydrous calcium silicates proceeds more slowly than that of the hydrated compounds, but more rapidly compared to that of anhydrous calcium aluminates The reactivity of β-C2S is higher than that of C3S in the carbonation, but the reverse is in the hydration. This fact is seen significant to resolve a reaction mechanism in the carbonation. The special feature of CaCO3 produced in the reaction of the anhydrous compounds is distinguished from that of the hydrated compounds, that is predominant of amorphous and differnt morphologic habit.

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