轻烧氧化镁对地质聚合物变形行为的影响及机理

Effect of Light-burned Magnesium Oxide on Deformation Behavior of Geopolymer and its Mechanism

为探索地质聚合物收缩补偿途径,研究了不同MgO掺量地质聚合物试体在不同养护条件(室温和38℃,相对温度RH>95%)下的变形行为,并采用X射线衍射、热重分析等测试方法研究掺入MgO地质聚合物的组成,分析了MgO影响地质聚合物变形行为的机理。结果表明:MgO对地质聚合物的变形行为有明显影响,且随养护条件不同而差异显著;掺入MgO可减小地质聚合物同龄期试体收缩,且掺量越大,减缩越大,但在通常养护条件下均没有表现出在波特兰水泥体系中显著的收缩补偿效应。MgO在地质聚合物中参与反应,且在不同养护条件下的反应机制有显著差异:常温条件下MgO优先与游离的[SiO4]4–反应生成高吸水性的硅酸镁凝胶;提高养护温度更利于促进地质聚合反应,加速对[SiO4]4–的消耗,从而抑制硅酸镁凝胶的形成。

For the exploration of a way to compensate the shrinkage of geopolymer, the deformation behavior of geopolymer bars with different contents of MgO was investigated via curing under different conditions （i.e., room temperature and 38 ℃ at relative humidity （RI-I） of 〉 95%）. The composition of the geopolymer was characterized by X-ray diffraction and thermogravimetry. The mechanism of MgO on affecting the deformation behaviour of geopolymer was proposed. The results show that the addition of MgO has an influence on the deformation behavior of geopolymer, and this effect is various with curing conditions. The addition of MgO decreases the shrinkage of geopolymer. The more MgO added, the less shrinkage would be. However, the effect of MgO in shrinkage compensation in geopolymer is not as significant as that in OPC system. MgO is involved in reactions in geopolymer based on dif- ferent mechanisms. MgO could bond with free [SiO4]4- to form magnesium silicate gel at a normal temperature, resulting in a high water absorption capacity. The increase of the curing temperature promotes the geopolymerization, and the reduction of the availabil- ity of free [SiO4]4- suppresses the formation of magnesium silicate gel.