In order to reexamine the heats of dissolution of gypsum and anhydride, calorimetric measurement of the following reaction couples were carried out at 25°C; CaSO₄·2H₂O-H₂O or H-R, CaSO₄ (II) -H₂O or H-R, gypsum saturate solution H-R and Ca-R₂-H₂SO₄ in which H-R and Ca-R₂ denote a strongly acidic ion exchange resin, hydrogen form and resin in Ca form, respectively. As shown in Fig. 3, there are distinct differences between this paper and published data as shown in Perry's handbook, viz.,
1) Heat of dissolution of gypsum in water was measured as 9.7kJ/mol (endothermal), the amount of which is greater than the handbook (0.7₅kJ/mol).
2) Difference between two data was also observed in heat of dissolution of anhydride in water such as 8.4 and 21.3₄kJ/mol.
3) Hydration heat of anhydride to gypsum was measured as 15.6kJ/mol comparable to the handbook (16.9kJ/mol).

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We have found that when using self-leveling flooring material (SL) made from anhydrite II gypsum occurs many cracks in the surface during the hardening process. The authors have found that the addition of silicone to the material is an extremely effective method for preventing these (initial) cracks.
In order to explain how the addition of silicone prevents (initial) cracking, we have attempted to identify the primary physical and chemical factors involved. The results of our research are as follows :
1) Adding silicone restrains both the shrinkage and the reduction in weight which occur during drying. We believe that, in turn, prevents (initial) cracking.
2) The silicone bleeds out to the surface of the SL when mixed with water, forming a thin membrane. This silicone membrane prevents evaporation of water from the SL, thus reduces shrinkage while drying.
3) Addition of silicone also reduces the small size of the pores in the hardened material and improves their distribution, greatly reducing shrinkage caused by drying over the long term.

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Considerable amount of natural zeolite has been used as an admixture for Portland cement in the People's Republic of China. This paper deals with a comprehensive characterization of inorganic admixtures such as two natural zeolites with different mineralogical compositions, a fly ash, a blust-furnace slag and a silica fume. Main crystalline component of zeolites were clinoptilolite and mordenite respectively, which were detected by X-ray diffraction analysis though their chemical composition were similar. The surface area measured by BET method of zeolites were approximately 13-25 times larger than that of fly ash and blast-furnace slag with an equal median diameter. Zeolites reacted with cement paste and formed ettringite at late ages. From these results natural zeolites were thought to be useful for concrete admixtures.

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The waste concrete is exhausting in very large quantity by scraping architectural concrete so that its treatment is recently attracting as big social problem on environmental disruption. Concerning to this problem, studies were made to investigate preparations of reclaimed cement and recycled concrete aggregate from waste concrete.
One kind of waste concrete (age of 52 years), two kinds of mortar (age of 1 year) using silica sand and limestone sand as aggregate respectively were chosen as sample. Those concrete and mortars were separated in three parts of coarse aggregate (upper 1 mm), fine aggregate (125μm-1 mm) and cement hydrate part (under 125μm) by sieving ground samples. As a countercheck for excess silica causing of inseparable fine aggregate came into the cement hydrate part, CaO/SiO₂ mole ratio of the hydrate part was adjusted to the ratio 2.8 as the same composition with normal portland cement clinker by adding limestone powder and then the hydrate part burned at 1450°C for 1h to prepare reclaimed cement clinker.
The X-ray diffraction patterns and chemical composition of the reclaimed cement clinker made by the above process were almost similar to those of normal cement clinker. The reclaimed cement was prepared by adding gypsum 3% to the clinker and grinding until Blaine surface-area of 3500cm²/g. However, the compressive strength for hardened mortar (cement/sand weight ratio 0.5) of the reclaimed cement was only about 60kgf/cm² after 28 days. This finding seemed to be caused by the presence of free lime (1.6%) remained in the cement.
In order to rise up the above strength, it was needed to adjust closely to the chemical composition of normal cement by adding required amounts of Fe₂O₃ and Al₂O₃ besides CaO. Consequently, the compressive strength of the improved reclaimed cement was much increased to 370kgf/cm² after 28 days which was almost the same to that of normal cement. As the above, it was apparent that the preparation of reclaimed cement from waste concrete was a useful process for recycling calcium resource.
In the other hand, the surface of aggregate particles separated by grinding waste concrete was usually covered with hardened cement hydrate but the rough surface was possible to change to the smooth surface to removed the hardened cement hydrate from the surface by dissolving with 0.5mol/dm³ HNO₃ solution. After finishing the dissolution, big crystals of a-type gypsum hemihydrate were obtained from the filtrate by adding 0.25mol/dm³ H₂SO₄ solution as the equivalence to make the hemihydrate.

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