活性MgO制备低碳排放复合胶凝材料及水化碳化机理研究

发布时间：2018-06-05 19:06

  本文选题：菱镁矿 + 活性MgO　； 参考：《华中科技大学》2013年博士论文

【摘要】：减少普通硅酸盐水泥(Ordinary Portland Cement,简称OPC)生产过程的碳排放,开发替代OPC的低碳水泥材料成为研究的热点。OPC高温煅烧下形成的过烧MgO(Dead-burned magnisa,简称过烧或死烧MgO)会产生后期膨胀,是OPC生产过程中需要控制的有害成分。近年来,低温制备的高活性MgO (Reactive magnisa,简称活性MgO)在低碳镁基水泥、水泥膨胀剂以及碳吸附材料中的应用受到了广泛关注。本文针对我国储量较大的菱镁矿资源,探讨低温煅烧菱镁矿制备活性MgO及其活性评价方法,以及制备的活性MgO单掺到OPC中对水泥水化过程、膨胀特性、碳化特性等的影响规律。主要包括以下内容： (1)菱镁矿低温煅烧制备活性MgO及其活性评价方法 在柠檬酸显色时间、MgO水化转化率的现有MgO活性评价方法基础上,针对菱镁矿600-750℃低温煅烧存在分解不完全的情况,首次提出低温制备活性MgO产物的修正水化转化率评价方法,并通过XRD、SEM、TEM等手段对活性MgO的水化产物进行表征。结果表明：焙烧温度越低,保温时间越短,单位质量MgO活性越高,但菱镁矿分解率越低。综合考虑菱镁矿分解率及MgO活性,采用自制回转焙烧炉,在焙烧温度700℃,保温时间180min制备活性MgO产物用于后续水泥材料的研究。 (2)活性MgO水泥体系浆体的体积膨胀规律及机理探讨 标准养护条件下,通过单掺MgO、复掺MgO与粉煤灰的掺料方式,研究不同活性MgO对水泥净浆体积变化的影响规律。通过模拟浆体的40-50℃的温度条件,设定水浸泡温度为40℃,通过XRD、SEM、DTA/TG、比表面积及孔径分析等分析手段,分析养护温度对浆体膨胀率以及水化产物基本性能的影响。水浸泡升温加速了水泥浆体的水化速度,单掺过烧MgO水泥净浆的膨胀率显著比同掺量活性MgO水泥净浆的膨胀率大。XRD结果表明,活性MgO水泥浆体,MgO在43.126°(2θ)衍射峰值较低,Mg(OH)2在37.995°(2θ)处衍射峰面积较大；过烧MgO水泥浆体呈现相反的规律。过烧MgO水泥浆体在32.546°(2θ)处出现高峰值的衍射峰。MgO的活性影响水泥水化产物的组成和结构,从而导致水泥浆体水化前后体积的变化。单掺活性MgO水泥体系最优掺量是8wt%；复掺活性MgO和粉煤灰的水泥体系,最优掺量是10wt%MgO和20wt%PFA。选择蒸压养护(80-180℃)的方式,加速MgO在体系中的水化过程。蒸养过程中浆体收缩与C-S-H凝胶失水,活性MgO的水化以及水泥水化产物的结晶有关。 (3)活性MgO水泥体系碳化规律及机理研究 以活性MgO与普通硅酸盐水泥熟料、粉煤灰为原料设定MgO和粉煤灰的掺量范围,进行净浆和砂浆的实验。碳化养护条件20±3℃、湿度70±2%,CO2浓度体积分数为5.0±0.2%,10.0±0.2%,20.0±0.2%和80.0±0.2%。通过XRD、SEM、FTIR、孔径分析等测试手段,分析净浆pH变化规律、C02吸收量、碳化深度以及砂浆强度。水泥浆体PM2-2(MgO掺量20wt%和20wt%粉煤灰)在5%C02养护90d,C02吸收量的最大值为27.30%。酚酞试剂测定碳化深度,无色区是浆体的完全碳化区,pH9.6。未碳化区pH为12.9,碳化反应区均有较高的pH,范围在9.6-12.9。砂浆碳化强度最大的样品PM3-1(MgO掺量10wt%,粉煤灰掺量30wt%),10%C02碳化养护14d、28d和90d的抗压强度分别为60.75MPa、53.69MPa和67.56MPa。 (4)活性MgO碱激发矿渣水泥体系体积变形 碱激发矿渣水泥(Alkali-activated slag,简称AAS)水化产物C-S-H凝胶的钙硅比、孔径结构特征造成AAS比OPC浆体更容易开裂。复掺活性MgO及粉煤灰可以减少碱激发矿渣水泥的干燥收缩和化学收缩。在碱激发剂的模数和掺量、粉煤灰掺量、MgO掺量的单因素实验基础上,采用表面响应法(RSM,Response Surface Methodology)实验设计四因素三水平的实验,得出体系最优配比为粉煤灰：矿渣的质量比FSR为0.4,碱激发剂的掺量10%,水玻璃模数1.6,MgO的掺量0.19。优化配方MgO:slag:fly ash为20：56.3：23.7时,砂浆试块28d抗折强度为7.29MPa,抗压强度44.58MPa。
[Abstract]:In recent years , high - activity MgO ( reactive magnisa , abbreviated as active MgO ) has been widely used in low - carbon magnesia - based cement , cement swelling agent and carbon adsorption material . In recent years , high activity MgO ( reactive magnum ) prepared at low temperature has been used in low - carbon magnesia - based cement , cement swelling agent and carbon adsorption material .

( 1 ) Low - temperature calcination of magnesite ore to prepare active MgO and its activity evaluation method

On the basis of the existing MgO activity evaluation method of the reaction time of citric acid and the hydration conversion rate of MgO , the method for evaluating the modified hydration conversion rate of active MgO product was proposed for the first time . The results showed that the lower the calcination temperature , the shorter the heat preservation time , the higher the MgO activity of the unit mass , the lower the decomposition rate of magnesite .

( 2 ) The volumetric expansion law and mechanism of active MgO cement system slurry

The effects of different active MgO on the volume change of cement paste were studied by means of single - doped MgO , MgO and fly ash . The effects of curing temperature on the swelling rate and the basic properties of hydration products were analyzed by means of XRD , SEM , DTA / TG , specific surface area and pore size analysis .
The MgO cement paste has a high peak value at 32.546 掳 ( 2 胃 ) . The activity of MgO affects the composition and structure of cement hydration products , which results in the change of volume before and after the hydration of cement slurry . The optimum mixing amount of single active MgO cement system is 8wt % .
The hydration process of MgO in the system was accelerated by selecting autoclaved curing ( 80 - 180 鈩，

本文编号：1983100