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低温氯氧镁水泥物相、水化动力学过程及其工程性能的研究

作者:完美论文网  来源:www.wmlunwen.com  发布时间:2019/10/24 9:42:32  

摘要:氯氧镁(MOC)水泥是以活性氧化镁,氯化镁和水为原料制备的一种气硬性胶凝材料。与传统硅酸盐水泥相比,具有快速凝固、高强度、碱度低、防火、低导热、高耐磨和抗盐卤腐蚀等优点而受到全世界的广泛关注。氯氧镁水泥在低温寒冷地区或者冬季施工时,展现出水化速率慢,强度增长慢,养护期结束强度较低以及制品体积不稳定等缺点。而水化反应温度和MgO活性是影响氯氧镁水泥水化产物形成和强度等性能发展的重要因素。本论文以高活性MgO等量替换菱苦土研究了低温(5~20℃)氯氧镁水泥水化过程和水化产物相的形成机理,然后通过水化热法测定MOC放热曲线,根据模拟的动力学参数分析MOC水化动力学行为。并用X射线粉末衍射(XRD)、水泥强度试验机、场发射扫描电镜(FESEM)、物理吸附仪等仪器对低温MOC进行表征。主要研究内容如下:

(1)在MgO:MgCl2:H2O=5:1:13(摩尔比)体系中,用不同活性含量的MgO制备氯氧镁水泥。对不同温度(5~20 ℃) 下MOC水化产物变化的研究表明,当水化养护温度低于15 ℃时,MOC水化产物开始出现3相[3Mg(OH)2·MgCl2·8H2O],温度越低,MOC中3相相对含量越高,而在MOC材料中起强度作用的5相[5Mg(OH)2·MgCl2·8H2O]的相对含量越低,导致低温制备MOC材料早期强度明显降低。提高MgO的活性可以促进低温MOC水化相选择性生成单一的5相,温度越低,生成单一5相的所需MgO的活性越高。本研究设计利用部分高活性MgO等量替换部分菱苦土制备MOC,成功诱导了低温MOC材料水化产物生成单一5相,并明显提高MOC早期水化反应速率和低温下氯氧镁水泥的强度,尤其是早期强度。当等量替换50%高活性MgO制备MOC,5℃下养护7d抗压强度可达75Mpa,相对对比样提高30.2%。

(2)在MgO:MgCl2:H2O=5:1:13(摩尔比)体系中,利用量热仪对高活性MgO等量替换菱苦土制备的MOC进行水化放热过程分析,采用Knusen方程计算了该MOC体系各温度下的水化动力学方程,计算得到了最大放热量P∞和半衰期t50。采用knodo模型计算出各水化阶段的反应速率常数k和反应机理常数N。结果表明;随水化温度降低,各水化阶段的的放热速率减少,水化反应历程延长;高活性MgO的替换缩短了水化反应历程,使诱导期缩短,加速期提前,水化放热速率加快。水化产物快速生成,水化反应很快进入扩散控制阶段,也使高活性MgO的等量替换菱苦土制备的MOC材料力学性能接近常温制备性能。

(3)采用氮吸附法表征了低温氯氧镁水泥的内部微观孔结构,研究了高活性MgO等量替换对低温MOC孔经分布的影响。并通过测量MOC尺寸变化率来表征氯氧镁水泥体积稳定性。分析微观孔结构参数与氯氧镁水泥体积形变和强度之间的对应关系,发现恒低温养护条件下的氯氧镁水泥孔隙较多,发生膨胀变形,抗压强度也较低。而高活性MgO替换的MOC体系,低温氯氧镁水泥试样内部的孔径得到优化,各级孔尺寸分布均变少,水泥内部的孔结构更加细致,水泥的平均孔径也变小,体积较稳定。

Magnesium oxychloride (MOC) cement is agas-hardening cementitious material prepared by using active magnesium oxide,magnesium chloride and water as raw materials. Compared with traditionalPortland cement, it has the advantages of rapid solidification, high strength,low alkalinity, fire resistance, low thermal conductivity, high wear resistanceand salt and halogen corrosion resistance. Magnesium oxychloride cementexhibits shortcomings such as slow hydration rate, slow growth, low strength atthe end of the curing period, and unstable product volume in special cold areasor winter construction. The hydration reaction temperature and MgO activity areimportant factors affecting the formation and strength of the hydrationproducts of magnesium oxychloride cement. In this paper, the low temperature(5-20℃) hydration process and the formation mechanism of the hydration productphase of magnesium oxychloride cement were studied by replacing magnesia withhigh activity MgO in equal quantities. Then, the heat release curve of MOC wasmeasured by the hydration thermal method, and the hydration kinetic behavior ofMOC was analyzed according to the obtained kinetic parametersthe. The MOC wascharacterized by X-ray powder diffraction (XRD), cement strength testingmachine, field emission scanning electron microscope (FESEM), physicaladsorption instrument and other instruments. The main research contents are asfollows:

(1) In a system ofMgO:MgCl2:H2O=5:1:13(molar ratio), magnesium oxychloride cement was preparedusing MgO of different active contents. The study on the change of MOChydration products at different temperatures (5~20 °C) shows that when thecuring temperature is lower than 15 °C, the MOC hydration product begins toappear phase 3 [3Mg(OH)2·MgCl2·8H2O]. The lower the temperature, the higher therelative content of the phase 3 in the MOC, and the lower the relative contentof the phase 5 [5Mg(OH)2·MgCl2·8H2O] in the MOC material, resulting in asignificant decrease in the early strength of the MOC material prepared at lowtemperature. Increasing the activity of MgO can promote the selective formationof a single phase 5 in the low-temperature MOC hydration phase. A lowertemperature gives a higher activity of MgO needed to generate a single phase 5substance. In this paper, the hydration reaction rate of MOC accelerates at alow temperature, and the hydration products selectively generate a single phase5 substance, and the compressive strength of MOC increases, especially theearly strength, when MOC is prepared by replacing a certain proportion ofmagnesia with a high activity MgO. When MOC was prepared by replacing 50% highactivity MgO with equal amount, the compressive strength of curing 7d at 5 °Ccould reach 75 Mpa, which was 30.2% compared with the control, and the earlystrength was obviously improved.

(2) In the system ofMgO:MgCl2:H2O=5:1:13(molar ratio), the hydration and exothermic analysis of MOCprepared by replacing high activity MgO with magnesia was carried out. Thehydration kinetics equation of the MOC system was calculated by Knusenequation. The maximum exotherm P∞ and half life t50 were calculated. Thereaction rate constant k and the reaction mechanism constant N of eachhydration stage were calculated using the knodo model. The results show thatwith the decrease of hydration temperature, the exothermic rate of eachhydration stage decreases and the hydration reaction process prolongs; thereplacement of high activity MgO shortens the hydration reaction process,shortens the induction period, advances the acceleration period, and thehydrates heat rate is accelerated. The hydration product is rapidly formed, andthe hydration reaction quickly enters the diffusion control stage. Themechanical properties of the MOC material prepared by replacing thehigh-activity MgO with the equivalent amount of rhododendron are close to thenormal temperature preparation performance.

关键词:氯氧镁水泥;低温;物相;水化动力学;孔结构

Magnesium oxychloride cement; lowtemperature; phase; hydration kinetics; pore structure

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