The hydration process of 12CaO · 7Al₂O₃ (C₁₂A₇) and 11CaO · 7Al²O₃ · CaF₂ (C₁₁A₇ · CaF2) were examined. It became clear that there were differences in hydrates between C₁₂A₇ and C₁₁A₇ · CaF₂. Cubic tricalcium aluminate hexahydrate (C₃AH₆) was formed from C₁₁A₇·CaF₂ at the very beginning of the hydration, but there appeared no C₃AH₆ in the case of C₁₂A₇. DTA and TGA curves indicated the presence of aluminium gel together with C3AH6.
The effect of fluoride ion was examined by the addition of various fluorides into C₁₂A₇. The time required for the formation of C₃AH₆ was shortened by the addition of HF, NaF, CaF₂, LiF or Na₂SiF₆ into C₁₂A₇. In the case of AlF₃, the time was not shortened. This suggests that fluoride ion plays an important role on the acceleration of C3AH6 formation and this also implies the presence of the compound formed from aluminium ion and fluoride ion.
By using the conduction calorimater, the correlation between the heat evolution curve and hydrates was observed.

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The influence of aromatic sulfonic acid on the hydration and the dissolution of CSH_0.5 and CH was investigated. Benzene sulfonic acid (BS), phenol sulfonic acid (PS) and sulfosalicylic acid (SS) were added. The rate of heat liberation was unaffected by BS, and was little affected by PS, though SS reduced remarkably its rate. These are affected on the kind of hydrophilic group and its number and position in the molecule. BS, PS and SS reacted with Ca²⁺ under a strongly alkaline condition, the combined Ca/acid ratios were 0.5, 1.0 and 1. 5 in mole, respectively, after 10 minutes. From the change of electric conductivity in case of SS, the formation of Ca-complex was confirmed. A stable 6-membered chelate ring is formed as shown in Scheme IV. On the other hand, these additives didn't react with Ca²⁺ under an acidic condition.
When the prepared gypsum plaster was dispersed into each additive solution at 25°C, the concentration of CaO in the liquid increased immediately after contact with solution. The retention period at the saturated concentration state is as follows :
BS (10 min) < PS (20 min) << SS (over 3 hr)
After the end of the retention period, a large quantity of CSH₂ was formed. Namely, the additive which formed a stable 6-membered chelate ring is able to prolong the retention period at the saturated concentration. It suggested to retard the rate of heat liberation. The amount of aromatic sulfonic acid adsorbed on the synthesized gypsum plaster in this period was measured by UV method. Consequently, BS wasn't adsorbed through this period, though, PS was adsorbed after initial hydration. The adsorption of SS began after the retention period.

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In the first, characterizations on four sorts of fly ash was carried out with chemical analysis and X-ray diffraction. The obtained results were compared with data on fly ash of 25 years ago. In the second, dissolution experiment of fly ash in acid solutions were carried out in order to know the behavior in acid solution. The results obtained were summerized as follows.
1) The chemical compositions of recent fly ashes were not so different from them of 25 years ago, but the content of insoluble residue of the formers was greater than one of the latters in analysis of soluble component to concentrated HCl.
2) Although crystalline materials in the fly ash of 25 years ago were composed of mainly aquartz and glassy substance, them in recent fly ash were composed of α- quartz and mullite. The increase of insoluble residue and the formation of mullite were considered as resulting from the recent burning technique of low temperature.
3) The amount of dissolution of fly ash in HCl solutions were not so much as that of blast furnace slag. When 100g of fly ash were pored into 1, 000 ml of 1N HCl solution, about 20 g of fly ash were dissolved in 24 hours at 30°C.
4) The dissolution ratios of CaO, Al₂O₃ and SiO₂ from fly ash were about 0.6, 0.13 and 0.09 in 1N HCl solutin in 24 hours at 30°C.
5) The dissolution ratio of Al₂O₃ from fly ash was larger in H₂SO₄ solution than in HCl solution.
6) Al₂O₃ in fly ash were activated by H₂SO₄ treatment and ettringite was easily formed in the reaction of fly ash-H₂SO₄ solution-Ca (OH) ₂.

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Basic refractories have been used for the burning zone of the lime kiln. The texture of basic refractory such as magnesia-chrome brick is classified into silicate bond and direct bond. Besides magnesia-chrome brick, magnesia-spinel brick is common for the lime kiln. Many results have been obtained in the actual use of these refractories and it is known that life of the linings normally depends on the texture of refractories.
Four different magnesia-chrome bricks in bonding texture and one magnesia-spinel brick were selected for the reaction test with lime. Samples were fired at 1400°C and kept for 4 hours in the test furnace.
After reaction test, appearance observation, X-ray diffraction, chemical analysis, polarization microscope observation and reflection microscope observation were taken for the test. Especially, changes of micro-texture were observed.
As the results, magnesia-chrome brick which has ideally developed direct bond showed the best behavior against lime. On the other hand the texture of magnesia chrome brick with silicate bond was decomposed by the migration of lime.
On magnesia-spinel brick, spinel clinker (mainly MgO·Al₂O₃) in the brick reacted with CaO, consequently it became 12CaO·7Al₂O₃. This reaction may cause gradually the decomposition of the texture when the brick is used for a long time in the actual kilns.

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