2004 Volume 11 Issue 309 Pages 105-112
Characteristics of alumina cement mortar containing colemanite or calcined colemanite are studied. Colemanite and calcined colemanite delay hardening of alumina cement mortar containing blast furnace slag powder (ACBB mortar). Calcined colemanite has stronger delaying effect because it elutes a significantly greater amount of boron as it contains a greater amount of boron and has a greater specific surface area than colemanite. ACBB exhibits practical strength at 1 day of age even though colemanite or calcined colemanite having the delaying effect is added in an amount of up to 10% of mass because alumina cement seems to have a higher hydration activity than portland cement. Furthermore, in the case of adding calcined colemanite, the compressive strength at 28 days age is increased to a higher value by adding the colemanite, and the compressive strength becomes a similar level to that to which no additive is added. Acid resistance of the alumina cement mortar is maintained, even when colemanite or calcined colemanite is added. They exhibit much higher acid resistance compared with mortar hardened bodies prepared using ordinary portland cement or blastfurnace slag cement class B. Colemanite functions as an inhibitor of conversion of alumina cement because Ca6Al2 [B (OH) 6] 9.8 (OH) 14.2·20H2O seems to form as a stable phase. From measurement results by XRD, the presence of colemanite could not be observed at 1 day of age, in other words it reacted.
