A STUDY ON THE ACCELERATORS FORS THE HARDENING OF PORTLAND CEMENT, I:Effect of Various Compounds on the Compressive Strength of Mortar and on the Amount of Lime Dissolving From the Cement in Water
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Employing a pulverized portland cement clinker supplied by a Japanese company and the mixture of 100 parts of the clinker and 2.5 parts of a pulverized gypsum, an investigation was carried out to find the influence of mostly soluble compounds upon the compressive strength of their mortars Water cement ratio and the ratio of the cement to the standard sand were 0.60:1.00 and 1:3, respectively. Specimens measured 5cm. in diameter and 10cm in height. The amounts of the compounds added varied from 1 to 5% of the clinker or cement for most of the specimens. The compounds comprised 12 sulphates, 6 nitrates, 12 chlorides, 5 bromides, ferric oxide, ferric hydroxide, barium hydroxide, sodium silicofluoride, benzoic acid, sodium acetate, ammonium carbonate, and ferric phosphate. The specimens were cured for 3 to 28 days, a few of them being heated in an autoclave for 5 hours at 120°C on storing them for 3 days.On the other hand, the concentrations in lime of the solutions which were prepared by stirring mixtures of the pulverized clinker or cement, a small proportion of 10 different salts, and distilled water 10 times as much as the clinker or cement for 15 minutes to 5 hours at the constant temperature of 30°C. The amounts of the salts ranged between 1 and 5% in most cases.The following conclusions may be drawn from the results obtained by the experiments:(1) All compounds except cupric sulphate, manganous sulphate, cupric chloride, benzoic acid, and sodium silicofluoride namely most of them, increased the early strength of the pulverized clinker.(2) As for the cement, ferric chloride increased its early strength strikingly and all chloride except lead chloride and cupric chloride were effective. Also calcium bromide. ammonium carbonate, and ferric sulphate encouraged the strength. However many sulphates, nitrates, ferric oxide, ferric hydroxide, and ferric phosphate were harmful. In other words, a large majority of the compounds reduced the strength and, even with the effective compounds, the percentage increases were by far lower.(3) No distinct reguralities were observed in the effects of the cations and anions of the added compounds on the compressive strength of the mortars.(4) On comparing these results to those reported by Goroku Kuniyoshi who had used the testing method of the Japanese specifications, there are considerable inconsistencies and differences between them. It is likely that the effect varies with the water cement ratio.(5) No definite relations were found between the amounts of lime dissolving from the clinker or cement in water and the strength of the mortars.
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公益社団法人 日本セラミックス協会 | 論文
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