Hydration and setting time of MgO-type expansive cement

✍ Scribed by Liu Zheng; Cui Xuehua; Tang Mingshu

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 259 KB
• Volume: 22
• Category: Article
• ISSN: 0008-8846
• DOI: 10.1016/0008-8846(92)90129-j

✦ Synopsis

The hydration and setting time of MgO-type expansive cement was investigated. The results show that the addition of MgO retards the initial hydration of the cements and increases the setting time. The causes for the retardation of hydration can be attributed to: (1) since the solubility product constant of Mg(OH) 2 is far less than that of Ca(OH) 2, and when MgO is added and Mg(OH) 2 is formed, the ionic product for calcium and hydroxyl ions [Ca2÷][OH'] 2, or Ca(OH) 2 saturation ratio, the ratio of Ca(OH) 2 concentration to saturated Ca(OH) 2 concentration under the same ionic strength is reduced in the liquid phase of the hydrating cement. And the time when the Ca(OH) 2 saturation ratio reaches the maximum is increased, the initiation of the second peak on the heat evolution curve of cement, i.e. the end of the induction period, is delayed; (2) Mg(OH) 2, which is formed by MgO hydration in a high alkali medium such as the liquid phase of hydrating cements, precipitates with a tiny crystallite size on the cement grains and forms a "protective layer," which retards further hydration of the cements.