Hydration on surface of artificial calcium aluminate aggregates and its characteristics

Hydration mechanism of calcium aluminate aggregate was examined. In order to confirm the hydration property of calcium aluminate aggregate, hydrate in the paste specimen which was mixed grinded calcium aluminate aggregate, Ca(OH)₂ and water was confirmed by XRD. And also hydrate in the paste which was added CaCl₂ to above paste was confirmed. The hydrates in the mortar with calcium aluminate aggregate were confirmed by XRD and TG-D TA, and these hydrates were observed by SEM image. In addition, the hydrates were confirmed by EDS and same examinations were carried out for the mortar with natural sand for comparison. Author confirmed that grinded calcium aluminate powder reacts with Ca(OH)₂ which is provided as a cement hydrate and it generates hydrocalumite. Furthermore, there was a property to change to Friedel's salt when a chloride ion acted. When the calcium aluminate is used for mortar as fine aggregate, a hydration was occurred at the aggregate surface and it was confirmed to generate hydrocalumite and hydrogarnet in the aggregate surface section. As a result, the possibility that a transition zone of mortar was modified by using the calcium aluminate aggregate was suggested. In the mortar which after salt water immersion, chloride ion penetration depth of mortar with calcium aluminate aggregate was smaller than ordinary mortar. And the hydrate formed layer was confirmed at the fine aggregate surface and its Ca/Al or Cl/Al molar ratio was similar to Friedel's salt. And hydrates which Ca/Al molar ratio is 1.5 to 2.0 were also confirmed on the surface of calcium aluminate aggregate.