Kiyoshi Asaga

Mechanisms and kinetics of C4AF hydration with gypsum

Abstract The mechanisms and kinetics of early stage C4AF hydration with gypsum was studied by measuring the heat of hydration with a conduction calorimeter. The heat of the reaction was 173 cal/ g-C4AF. The reaction equation was estimated to be C 4 AF + 4 CaSO 4 ·2 H 2 O + 35 1 3 H 2 O → 4 3 C 3 ( A 0.75 , F 0.25 )·3 C S H 31 + 2 3 FH 3 The equation for rate of hydration was ζ = 0.25t as the thickness (ζ) or hydrated C4AF increased from 0 to 0.6 μm.

Quantitative determination of fly ash in the hydrated fly ash - CaSO4·2H2OCa(OH)2 system

Abstract For the quantitative determination of fly ash in hydrated fly ash - CaSO 4 ·2H 2 OCa(OH) 2 system, various kinds of selective dissolution were evaluated using pastes made from a single representative fly ash. Selective dissolution using picric acid-methanol solution was found to be adequate. Selective dissolution using picric acid - methanol + water can also be used, when it is necessary to save time, although rather bigger corrections are needed. Reproducibility of the determination by both methods was found to be satisfactory, as the standard deviation of the measurement was within 0.23 – 0.55%. Several dissolution experiments were also carried out to obtain the basic information related to this technique.

Influence of sodium aromatic sulfonates on the hydration of tricalcium aluminate with or without gypsym

Abstract The influence of sodium aromatic sulfonates on the hydration of C 3 A alone or plus gypsum was investigated specially relating to the molecular structure of the additives. It was found that the existence of sodium aromatic sulfonates retards the hydration of C 3 A either with or without gypsum, and the degree of retardation depends upon the structures of sodium aromatic sulfonates.

Preparation and hydration of β-C2S without stabilizer

Abstract The preparation method of β-C 2S without stabilizer, and their hydration characteristics were studied. β-C2S is formed when γ-C2S is heated at about 1000°C or about 1500°C. The hydration kinetics of β-C2S produced from α′-C2S is markedly different from that from α-phase. Ca(OH)2 is hardly produced in the hydration of β-C2S without stabilizer. Formed C-S-H has a composition of C/S ⋍ 2 .

A study of hydration of amorphous calcium aluminate by selective dissolution analysis

Abstract Amorphous calcium aluminate consisting of CaO and Al 2 O 3 in a composition close to 12 : 7 in terms of mole ratio (hereinafter Am.C.A) was synthetized by quenching after fusion in an electric furnace. The Am.C.A hydrates immediately after contact with water and sets in 3 to 5 seconds. It was found that selective dissolution by methanol solution of salicylic acid was appropriate as a method of measuring the degree of hydration of Am.C.A. which reacts so rapidly. The degree of hydration of Am.C.A and crystalline 12CaO · 7Al 2 O 3 (hereinafter “C 12 A 7 ”) was measured by this method, and it was found that the rate of hydratio of Am.C. A at the initial stage is extremely high in comparison with C 12 A 7 .

Influence of Ca(OH)2 and CaSO4 · 2H2O on hydration reaction of amorphous calcium aluminate

Abstract The influences of Ca(OH) 2 and CaSO 4 ·2H 2 O on the hydration of amorphous calcium aluminate with the chemical composition similar to C 12 A 7 were studied by determining the degree of hydration according to the selective dissolution method. The hydration reaction of amorphous calcium aluminate progresses very rapidly and amorphous AH 3 is produced along with C 2 AH 8 . The reaction is retarded slightly by the addition of Ca(OH) 2 . When a small amount of CaSO 4 · 2H 2 O is added, the degree of hydration is increased compared with the case of no addition. However, the hydration reaction is greatly retarded, in the presence of large amount of CaSO 4 · 2H 2 O When Ca(OH) 2 and CaSO 4 · 2H 2 O are added, the retarding effect is larger than in the case of adding 1 mole of CaSO 4 · 2H 2 O alone.