Effect of Additive Agents on Consolidation and Mechanical Properties of Alumina Cement
Mariko NAKANO, Takeshi SHIONO and Yasunori OKAMOTO
Abstract:Alumina cement hardens rapidly and its early-age strength is very high, compared to portland cement. So alumina cement is expected as rapid hardening cement. In spite of the excellent properties of alumina cement, however, the cement has not been widely used, because the cement does not have long-term strength, due to the conversion of crystalline phase. At first, alumina cement reacts with water to form the hydrates of CaO¥Al2O3¥10H2O and 2CaO¥Al2O3¥8H2O, resulting in high strength. Then the hydrates subsequently decompose to a mixture of 3CaO¥Al2O3¥6H2O, Al(OH)3 gel and water. This process causes an increase in porosity, leading to a decrease in strength. In order to examine the effect of additives on crystalline phases and long-term strength, in this paper, consolidated alumina cements containing fumed silica and water-reducing admixture were prepared and evaluated the compressive strength, the changes of crystalline phase and the changes of microstructure with time. The water-reducing admixture was effective to inhibit dissolution of CaO¥Al2O3 component@in alumina cement. The consolidated alumina cement with both fumed silica and water-reducing admixture didnft form the first hydrate of CaO¥Al2O3¥10H2O and had long-term high strength. Formation of CaO¥Al2O3¥10H2O was inferred to be important for strength degradation due to the conversion. Key Words:Alumina cement, Fumed silica, Water-reducing admixture, Conversion, Crystal phase