Physical Properties and Hydration Behavior of 3CaO⋅Al2O3 Composition by Quenching after Fusion

Abstract

The melt of 3CaO⋅Al2O3 (G-C3A) composition in the presence of a small amount of SiO2 was synthesized by rapid quenching after fusion. Furthermore, the physical properties and the hydration behavior of G-C3A were investigated. G-C3A results in a lowering of lattice constant, a decrease of specific gravity and an increase of free CaO compared with C3A. The hydration was not completed even on 10 days curing, and 3CaO⋅Al2O3⋅6H2O hydrate grew very slowly. It is thought that Al(OH)4- eluted from G-C3A is remarkably depressed against Ca2+. The molar ratio (CaO/Al2O3) in case of G-C3A was given 2.7 after 10 days curing but closely approached to 1.0 after 6 hours curing in case of C3A. Namely, as glass phase is formed on G-C3A surface, the strain occurs in inner layer. Therefore, it is difficult to elute Al(OH)4- by breaking -Al-O-Al- bonds. Although the elution of Al(OH)4- by NaOH is considerable, the growth of the hydrate cannot be expected because of depression of the elution of Ca2+. The results of surface analysis by ESCA showed that the binding energy of inner shell electron of Ca, Al, and Si combined with O (oxygen) in G-C3A is 0.7-0.8eV higher than C3A. Consequently, as the elution of Ca2+ and Al(OH)4- is depressed, the hydration reaction becomes inactive.