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

本财政年度（1997年）研究的主要目标是通过(1)对水泥粉的高密度颗粒进行最密集的填充以减少吸水，以及(2)通过碳化对纤维增强水泥板进行化学表面改性以使材料表面孔隙结构致密化，来增强非石棉纤维增强水泥板（FRCB）的抗冻性。为了达到(1)的目的，采用双级冲击器（DSI）在高速空气涡流中使水泥粉混合物中的致密颗粒球化，获得了高密度水泥生粉。这种致密球化水泥粉使FRCB的吸水率从制备时的15-20%大幅降低到4-5%。如此大幅度的吸水率降低使得FRCB的抗冻性能得到了极好的改善。为达到(2)的目的，在50-60℃的加热条件下，在2-3 atm的压缩条件下，吸收碱土（Ca^<+2>或Mg^<+2>）溶液的商用FRCB的碳化。通过在frcb表面析出微晶MgCO_3或CaCO_3，使CO_2气体更加致密。这样的表面碳化使样品的霜耐久性大大提高。目前，从无机化学的基本观点出发，仍在不断研究Mg <+2>溶液比Ca <+2>溶液更致密碳化的优越性。为了阐明frcb结霜机理的基础研究，采用冷却DSC技术比较了几种陶瓷氧化物表面的水的热力学稳定性，测量了冻结焓和冻结开始温度，从室温到-196℃。实验结果表明，随着阳离子与氧原子之间的化学离子键力的减小，陶瓷氧化物表面的水键力增大。此外，非结晶结构表面的水比良好结晶表面的水具有更强的束缚力。地表水上这些结合力的厚度取决于化合物、结晶度和氧化物的疏水性，但粗略估计约为20-30分子层（即6-10纳米）。少

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