The Behaviors of Gluconic Acid Derivative in Hydration of CaO⋅Al2O3

The hydration of cements with additives were often changed remarkably by the added amounts. Authors studied the hydration of CaO⋅Al2O3 in the presence of calcium 2-oxogluconate, whic hhave two functional groups of -COON and >C=O. When this compound was dissolved in Ca(OH)2 solution, Ca-complex was formed in some cases, and Ca-coprecipitate in other cases. The process is given as reaction formula (3). The hydration of CaO⋅Al2O3 dispersed in admixture solution at 25°C proceeded in three different ways (Types A, B and C) according to the admixture concentration. Anyhow, to be common with initial hydration stage passes into as follows; inherent effluent of calcium and aluminium from CaO⋅Al2O3→formation of Ca-complex→production of Ca-coprecipitate. Above process is an application of formula (3). These differences were supposed to be caused by the different quantities of reacted calcium and aluminium. The setting time was determined by the retention period of effluent phenomenon or the formation of Ca-complex, when admixture concentration was lower. And coprecipitate was formed as the coating on CaO⋅Al2O3 surface at higher concentration. Consequently, the states is classified into three ways such as the extremely thin coating of coprecipitate or the detaching phenomenon of coating or the stable thicker coating of grape state. These hydration model was illustrated in Fig. 12. Ca-complex is stable (1:1) complex in liquid phase. On the other hand, Ca-coprecipitate is amorphous substance, it is not simply Ca-salt of 2-oxogluconate. The gel in hardened bodies using this admixture has been induced by the formation of Ca-complex given as formula (3), its structure is assumed as Scheme II.