硼酸对硫氧镁水泥力学性能的影响

Effects of Boric Acid on the Properties of Magnesium Oxysulfate Cement

硫酸浸出法制备硼酸的废弃母液经过浮选法分离产生的硫酸镁中通常含有硼酸等杂质,为了研究硼酸对硫氧镁水泥凝结硬化及力学性能的影响,以改性硫氧镁水泥(MOS)为基础体系,测试了硼酸含量对硫氧镁水泥凝结时间、抗压和抗折强度的影响,讨论了硼酸对硫氧镁水泥抗水性、水化产物及微观形貌的影响。结果表明:硫氧镁水泥的凝结时间随硼酸含量的增加而延长;硼酸可以明显降低硫氧镁水泥的早期强度,对后期强度的降低作用不及早期明显;试件浸水28 d后,较高含量的硼酸提高了试件抗压强度的软化系数,而降低了抗折强度的软化系数,因此硫酸镁中硼酸含量不应超过0.7%;硫酸镁中硼酸含量不影响硫氧镁水泥水化产物的组成,但降低了水化产物的结晶度并改变其显微结构。

In the production of boric acid by sulfuric acid leaching method, the magnesium sulfate in mother solution spearated by the flotation process always contains some impurities such as H3BO3 and so on. In order to determine the effects of boric acid on the property of magnesium oxysulfate cement, the basis system of modified magnesium oxysulfate cement was establish, the effects of the boric acid on the setting time, compressive and flexural strength of magnesium oxysulfate cement was measured, the effects of boric acid on water resistance and hydration products and microstructure of magnesium oxysulfate ce- ment were discussed. The results show that the setting time of magnesium oxysulfate cement is retarded with the increase of the content of boric acid. The existence of boric acid can reduce significantly early strength of magnesium oxysulfate cement, and their effect is not significant on strength of 28 d or 56 d. Boric acid improve the softening coefficient of compressive strength and reduce the softening coefficient of flexural strength after immersion 28 d. So the maximum content of boric acid in magnesium sulfate cannot exceed O. 4%. The boric acid have no effects on hydration products of magnesium oxysulfate cement but decrease crystallization of hydration products and change its microstructure.