DEVELOPMENT OF HIGHLY DENSIFIED FIBER-REINFORCED CEMENT BOARDS DESIGNED BY PROPER STRUCTURE OF PORES

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The main objectives of the research in this fiscal year (1997) are the enhancement of frost durability of non-asbestos fiber-reinforced cement boards (FRCB) by (1) the densest packing of high densified granules of the cement powder in order to reduce the water absorption, and by (2) the chemical surface modification of FRCB through the carbonation in order to densify the surface pore structure of the materials. For the aim of (1), the high-densified cement raw powder was obtained by the double staged impactor (DSI) which could spheroidize the dense particles from the cement powder mixture in a high speed air vortex. Such a dense spheroidized cement powder made drastically reduced the water absorption of the FRCB from the 15-20% of as fabricated to 4-5% in this research. Such a great decrease in water absorption enabled the excellent improve of frost durability of the FRCB.For the aim of (2), the carbonation of the commercial FRCB being absorbed alkali-earth (Ca^<+2> or Mg^<+2>) solutio … More n under the conditions of warming in 50-60ﾟC and compressing in 2-3 atm.of CO_2 gas enabled denser by precipitation of micro crystalline MgCO_3 or CaCO_3 on the surface of the FRCBs. Such a surface carbonation made the frost durability of the samples so much. Now the superiority of such denser carbonation by Mg^<+2> solution than Ca^<+2> one is now still continuously researching from the fundamental inorganic chemical point of view.For the fundamental research on the mechanism elucidation on frost action of the FRCBs, the thermodynamical stability of water on the surface of several ceramic oxides was compared by cooling DSC technique measuring a freezing enthalpy and an onset temperature in freezing from a room temperature to -196ﾟC.As the results of experiments, it was found that the water bound force from the surface of ceramic oxides increased with the decreases in the chemical ionic bonding force between a cation and an oxygen atoms. And moreover, the water on the surface of non-crystalline structure has much stronger bound force than that on a well crystallized surface. The thickness of these bound force on the surface water depends on a compound, a crystalinity and a lyophobicity of the oxide, but was roughly estimated as about 20-30 molecular layrs (i.e., 6-10 nm). Less