1. V/cmが900-3000ボルトの範圍内に於ては本測定の精度では試料の厚さの影響は無視してよい。
2. 滑石河東磁土系焼成物の組成と400℃に於ける絶縁抵抗の關係は次式で表はされる。
logρ=-0.0296κ+4(at400℃)
但しρはMΩ單位, κは焼成物中の河東磁土の百分率
3. 河東磁土燒成物は約0.9%のアルカリを含有するが, アルカリを含有せざる場合には恐らく
logρ=-0.01κ+4(at400℃) と推定した。
4. 固有抵抗が400℃にて100MΩ以下なる場合の實用的な測定方法について述べた。

抄録全体を表示

The presents author, in continuing the previous studies (This Journal, 1934, 42, 273, 628, 688; 1935, 43, 215, 572; 1936, 44, 22, 617, etc.), report here the results of various comparative tests on various kinds of cements on the market in the spring of this year, in which high siliceous mixed Portland cements were recently commenced to produce in large scale in some factories. The principal results of the present report were abstracted from the original Japanese paper, as following:
(1) Two series of cement samples were collected from the market and tested their chemical compositions, which are tabulated in the following table 1.
Table 1. Results of Analyses of Chemical Compositions
(2) These 2 series and 14 cement samples were nextly compared on some physical properties, fineness, specific gravity and time of setting, which results are shown in the following table 2.
Table 2. Results of Comparison of Physical Properties
(3) The strengths of mortars of these cement samples were tested by several ways, as following:
Table 3. Results of Strength Tests of 1:3-Cement Sanl Non-Plastic Mortar
(a) 1:3-cement sand non-plastic motrars, which are in both standards of the Japanese Engineering Standard for Portland cement (JES 28) and blast furnace slag cement (JES 29), were tested on their strengths and the results were obtained, in table 3,
(b) 1:2-cement fine sand plastic mortars, which were modified by the present author from the method of Prof. M. Ros in Switzerland or of Dr. G. Haegermann in Germany, were tested on their bending and compressive strengths by using the prismatic test piece (4×4×16cm).
(c) 1:1-cement fine sand plastic mortars were also tested on their bending and compressive strengths by the same size prisms, only different in the amount of water, i.e., 1:2-mortar of 65% water-cement ratio and 1:1-mortar of 45% water-ceweut ratio.
(d) 1:1:2-cement-fine sand-standard sand plastic mortars were also moulded with 50% water to cement and their bending and compressive strengths were also tested by using of the same size prismatic test pieces
All these results are tabulated in the following table 4.
Table 4. Results of Strength Tests of 1:2-, 1:1:2- and 1:1- Cement-Fine Sand or Cement-Fine Sand-Standard Sand Plastic Mortar
It is from these results clearly seen, that low-heat special Portland cements (No. 490 and C) were considerably low grade cements of lowest strength at short curing days (3 and 7 days), and on the contrary high silica mixed Portland cements (No. 492-494 and E-G) were remarkably high grade cements having largest strength already at short curing days.
(4) The author is now further studying on various points, i.e., resistance to sea water and aggressive salt solution, heat of hydration, expansion or contraction, etc., which will he reported in next papers.

抄録全体を表示