外加剂对氯氧镁水泥水化过程影响

Influence of admixtures on hydration process of magnesium oxychloride cement

为改善氯氧镁水泥(MOC)水化速率快、凝结时间短的特性,选择适宜的聚羧酸减水剂和某酸类缓凝剂掺入到MOC中以提高水泥的和易性。首先,通过水化热试验研究了基准MOC水化历程,并划分了水化阶段,运用水化动力学方法研究不同水化阶段的主要受控因素;然后,分析外加剂对MOC水化放热量、水化速率、水化产物类型及形貌的影响,采用动力学方程对比研究了外加剂作用下MOC水化历程的变化;最后,以旋转黏度试验表征外加剂作用下MOC水化过程的变化,以浸水后力学强度与未浸水强度的比值表征外加剂作用下MOC耐水性变化。研究结果表明:MOC水化过程与硅酸盐水泥类似,可分为起始期、诱导期、加速期、减速期和稳定期,其中加速期阶段水化速率完全受控于结晶成核和晶体生长,之后相边界反应和扩散因素逐渐影响水化速率;MOC结晶成核和晶体生长速率直接影响水泥浆体的凝结时间,降低MOC水化速率的主要措施为控制其结晶速率;掺入减水剂、缓凝剂等外加剂并没有改变MOC水化产物,但其晶体形貌得到改善,浸水试验表明改善后的晶体形貌耐水能力更加优异;减水剂提高了浆体流动度,缓凝剂能够有效延长水化诱导期,加速期向后推迟了约2 h,但会小幅降低MOC的力学强度;旋转黏度试验表明添加外加剂有利于提高MOC的流动度。

To further enhance the rapid hydration rate and short setting time of magnesium oxychloride cement(MOC), suitable polycarboxylic acid water reducer and an acid retarder was added to the MOC to improve its workability. Firstly, the hydration process of a standard sample of MOC was explored, and the hydration stage was analyzed through the hydration heat test. The main control factors at different hydration stages were investigated using the method of hydration kinetics. Furthermore, the effects of admixtures on MOC hydration heat release, hydration rate, hydration product type, and morphology were then analyzed. Kinetic equations were used to compare the changes in the MOC hydration process under the action of admixtures. Finally, the rotational viscosity test was used to characterize the changes in the MOC hydration process under the action of admixtures, and the ratio of mechanical strength before and after immersion was used to characterize the water resistance under the action of admixtures. The results show that the MOC hydration process is similar to that of Portland cement and can be divided into initial period, induction period, acceleration period, deceleration period, and stable period. The hydration rate in the acceleration phase is completely controlled by crystal nucleation and crystal growth under acceleration period, after then the phase boundary reaction and diffusion factors gradually affect the hydration rate. Therefore, the crystallization nucleation and crystal growth rate directly affect the setting time of MOC, and a major way to reduce the hydration rate of MOC is to control the crystallization rate. The hydration product of MOC is unaltered by adding a water reducing agent and retarder, but admixtures change the crystal morphology and improve the water resistance. The immersion test shows that the improved crystal morphology is better for water resistance. The water reducing agent improves the fluidity of the slurry. The retarder effectively prolongs the hydration induction period, and postpones the acceleration period for approximately 2 h, but the mechanical strength of MOC is slightly reduced. The rotational viscosity test shows that admixtures are beneficial for improving the fluidity of MOC. 4 tabs, 15 figs, 33 refs.