On the Hydration of Glassy Slag-Minerals of the System Gehlenite, Melilite and Akermanite
1963 Volume 71 Issue 806 Pages 84-90
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1963 Volume 71 Issue 806 Pages 84-90
There are some papers concerning the influence of MgO on the strength of blast furnace cement using synthetic slag containing different amount of MgO. And up to 5-10% MgO no decrease in strength but instead some inclease in long term strength was observed leading to the conclusion that MgO would be plying the similar roll to CaO. This method is practical but will make the problem complicated.
The authors, have prepared 5 samples of glassy slag containing stimulating agents and different amount of MgO to study the hydraulic properties in room temperature and in autoclave.
(1) Hydration in room temperature
Next to gehlenite (J. Ceram. Assoc. Japan, 68, 307, (1960)) the progress of hydration of a knid of melilite, and of akermanite added as stimulant Ca(OH)2 and CaSO2⋅2H2O was studied. The crystalline substance found in the hydration product of melilite was similar to that of gehlenite, whereas no crystalline phase was obtained in the hydration product of akermanite.
Up to 28 days the amount of hydration of both samples was 50-55% giving no profound difference. As far as the present experiment concerns no sharp difference between the hydration of the two species was observed except the separation of the crystalline substance.
(2) Hydration in autoclave
The same samples were hydrated under pressure. The conditions were; temperature, 100°, 125°, 150°, 175°C; time 0.5, 1, 2, 4, 8 hrs.
The strength of the hydrationproduct at 100°C increased with increasing Al2O3 content, and the reaction of CaO ran parallel with the amount of Al2O3. In this case CaO-Al2O3-H2O was found to be main reaction product.
On the contrary, at 125°C the strength showed a marked fall with increasing Al2O3, which might due collaps of the strength revealing product of the system CaO-Al2O3-H2O.
The hydration at 175°C the strength increased with increasing Al2O3, where the principal crystalline hydrate was found to be as 3CaO⋅Al2O3⋅SiO2⋅4H2O (Kalousek, J. Am. Ceram. Soc., 40, 74, (1957)).
The samples containing more MgO showed generally low strength, which increased monotonausly with temperature and time. The addition of 20% crystalline silica powder, however reversed the trend giving higher strength with increasing MgO content.
In these cases the hydration product was amorphous. In the eyes of composition Al2O3 was effective as a strength developing agent when only basic stimulant was used, but with the addition of SiO2, MgO became more effective.
