Hydration Behavior of LD Slag at Autoclave Test

Abstract

Although autoclave test is often employed for evaluating the expansion potential of LD slag, the conditions for the autoclave test have not been yet defined. As a fundamental research on the selection of the suitable conditions for the autoclave test, an investigation was made concerning with the effect of the conditions on the hydration behavior of LD slag (i.e., the degree of hydration, hydrating mineral phases and hydrates), and various test procedures were compared.
The influence of the steam pressure and treatment time of the autoclave test, and particle size and free lime contents of LD slag on the degree of hydration and disintegration of LD slag were examined by changing the steam pressure from 3 to 45kg/cm², the treatment time from 3 to 24hr, and the mean particle size from 0.25 to .17.5mm. The degree of hydration is well defined by these autoclave test conditions. The degree of disintegration is varied with the change of the particle size.
Mineral phases, such as 2CaO•SiO₂, 2CaO•Fe₂O₃, (Mg, Fe)O, and unassimilated lime and magnesia were observed in this experiment. The influence of the autoclave test conditions on these mineral phases was examined by the autoclave treatment of polished samples and X-ray diffraction. Hydrates were identified and estimated by X-ray diffraction and TG-DTA. The kinds of hydrating mineral phases and hydrates did not vary with the changes in the autoclave test conditions. Hydration of LD slag was caused substantially by the lime solid solution and unassimilated lime. A slight degree of hydration of unassimilated magnesia, 2CaO• SiO₂ and 2CaO•Fe₂O₃ phases was observed. The unassimilated magnesia containing small amounts of FeO and MnO was disintegrated to some extent. Discussion was made about the mechanism that a particle of LD slag expand and then disintegrate.
Autoclave test conditions for relative comparison of expansion potential of LD slags need not to be specifically limited. Therefore it was found that any autoclave test conditions which can ensure a degree of hydration high enough for the measurement of expansion and are practical in other respects are useful. The difference in the expansion potential of LD slags could be detected by any autoclave test procedures for the measurement of volume expansion disintegration and weight increase.