The surface hydration of calcium carbonate has been studied. In particular, the effect of existing Ca (OH) ₂ like layer on adsorption of acetic acid was investigated. The surface hydration for heavy calcium carbonate was performed as follows. After heating the calcium carbonate at 570°C under reduced pressure, the hydration was carried out exposing under 95rh%. The presence of hydroxide ions in Ca (OH) ₂ like layer was confirmed by FT-IR. Surface properties of hydrated calcium carbonate were examined by adsorption of acetic acid, TPD and TPD/GC. The results are summarized as follows. (1) There was no Ca (OH) ₂ like layer on the surface of untreated heavy calcium carbonate. (2) Ca (OH) ₂ like layer was produced more than 5-7 layers on the surface of heavy calcium carbonate by surface hydration after the heat-treatment above 570°C. The amount of Ca (OH) ₂ like layer increased with rising of the heat-treatment temperature. (3) The desorbed behaviors of acetic acid chemisorbed on various calcium carbonate surfaces were classified into two types. One is desorbed as acetic acid molecules and the other is desorbed as decomposed substance. The amount of decomposed substance increased with the amount of Ca (OH) ₂ like layer. (4) The amount of acetic acid chemisorbed on the surface hydrated calcium carbonate increased as compared with the untreated heavy calcium carbonate. The surface property of heavy calcium carbonate became to resemble surface of colloidal calcium carbonate by surface hydration.

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The coating of amorphous magnesium silicate powders with CaCO₃ using dilute solutions containing CaCl₂ and NaHCO₃ results in the powder where needle-like crystals are expanded radially. The powders coated with CaCO₃ would be widely useful industrially, because the powders have a large surface area and would provide good contact with solvents. We investigated the relationship between the shapes or crystal phases of the powder coated with CaCO₃ and coating conditions in order to clarify the morphology of the coated powder. The formation of coated powder was much influenced by the initial conditions of the coating, and the crystal phase of coated powder was mostly determined by the conditions on the surface of the core powders at the initial stage. The presence of OH groups and magnesium on the core powder is essential to the formation of coated powder that has radially expanded needle-like crystals. In our experiments, the particle size of the powder was controlled by coating with CaCO₃ several times and adding polyvinyl alcohol little by little.

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A study was made to investigate synthesis slaked lime with dispersed ultrafine particles formed by hydrating quick lime in water and water including alcohol or surfactant.Slaked lime was synthesized by adding the water (H₂O/CaO molar ratio 1.2-1000) including alcohol (concentration of 0-70 vol%) and surfactant (surfactant/CaO weight ratio 0-0.03) to quick lime which was burned lime stone at 1000°C for 1 hour. Furthermore, the hydration was used open system and closed system reactor for accompanying with heat change. The characterization of product was determined by means of X-ray diffraction, specific surface area measurement, scanning electron microscopic observation and particle size distribution measurement.
The specific surface area of slaked lime formed in open system reactor was enhanced with decrease of H₂O/CaO molar ratio and was approximately 24 m². g^-1 in H₂O/CaO molar ratio 2. In the case of closed system reactor, minimum H₂O/CaO molar ratio for hydrating quick lime was decreased till 1.6 because the water was hardly evaporated. The particle size of slaked lime aggregate was small compared with that of open system reactor. The specific surface area of slaked lime formed by adding alcohol in open system reactor was rose with increase of the concentration, the slaked lime formed with concentration of methanol 70 vol% was ultrafine particle with specific surface area 53 m². g^-1. Therefore, the high dispersively slaked lime with ultrafine particle was synthesized by adding the both methanol and surfactant in water.

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Accelerated chloride ion penetration test was executed to quantitatively evaluate the effects of the type of cement, water-cement ratio and the type of coarse aggregate upon properties of normal strength, high-strength and high-strength lightweight concretes using various blended cements. We proposed a solution of Fick's diffusion equation taking into account the effect of water-cement ratio, type of cement and type of coarse aggregate. The chloride ion diffusivity of concretes was also discussed in terms of water-air permeability and total pore volumes.
Màjor findings are as follows.
(1) Use of blended cement and decrease of water-cement ratio were able to improve chloride permeability.
(2) Chloride permeability of high-strength lightweight concrete was larger than that of concretes using crushed stone coarse aggregate.
(3) Chloride ion diffusivity in concrete became greater when water-cement ratio increased and became smaller when the penetration duration became longer.
(4) Chloride ion diffusivity in concrete showed good correlation with water-air permeability and total pore volume at water-cement ratios from 40% to 60%, but became constant regardless of the water-air permeability and total pore volume at water-cement ratios from 30% to 40%.

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Here is reported some flocculation properties of lake sediment using a flocculant which is recently developed (herein “flocculant T”) for lake sediment. Since the flocculant T contains large amount of free lime with small amount of chlorine and clay mineral, dewatering and decreasing of weight occur effectively. The flocculant T is produced through a cement producing process and the cost is low. This contains few soluble chlorine and sulfuric acid comparing with common flocculant, therefore the dewatered cake is useful for a cement raw material.
As the results, handling efficiency of the filter pressed cake was same as the cake using common flocculants. The content of hazard elements and suspended solid in drainage is negligible small. But drainage shows high pH, therefore neutralization treatment is necessary.

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