Monitoring of Hydration in Cement Systems by Broadband Time-Domain-Reflectometry Dielectric Spectroscopy

通过宽带时域反射介电谱监测水泥系统中的水化

• 批准号: 0700699
• 负责人: Nathaniel Hager
• 金额: $ 18.87万
• 依托单位: Elizabethtown College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-05-01 至 2012-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0700699&HistoricalAwards=false
• 关键词: Monitoring; Hydration; Cement; Systems; Broadband

Prior work in our laboratory demonstrated a continuous monitoring of the dielectric relaxation spectrum in hydrating portland cement over the frequency range 10 kHz to 8 GHz from initial mixing to several weeks cure. Measurements were made using broadband Time-Domain-Reflectometry Dielectric Spectroscopy with a 35 ps stimulus and an embedded capacitance sensor. Three fundamental signals were identified, corresponding to unreacted free water, bound-water attaching to developing microstructure, and grain polarization. The three signal components were fit to appropriate molecular models as a function of cure time and monitored throughout the process. The result is 1) a free-water relaxation which monitors the disappearance of water into hydration and thus follows percent hydration, and 2) a bound-water relaxation which monitors water attaching to developing microstructure and thus monitors formation of this microstructure, and 3) a grain-polarization relaxation which monitors development of this microstructure.The proposed research will now expand this investigation to rigorously compare signal changes occurring in each component with chemical and material changes through a combination of analytical measurement, chemical variation, and experimental investigation. Measurements may include, but are not limited to: Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Thermoporometry, Quasi-Elastic Neutron Scattering (QENS), optical microscopy, and standard mechanical compressive-strength testing. Specific tasks include 1) extending measurement resolution to near 10 GHz to better resolve individual free- and bound-water components, 2) correlating the disappearance of free water near 10 GHz with the increase in hydration as determined by DSC and Thermogravimetric analysis, 3) correlating the increase in bound water near 100 MHz with the formation of reaction products as determined by QENS, microscopy, and other methods, 4) Estimating the free-water loss to evaporation by instrumenting a large test cylinder with sensors at varying depths and determining moisture gradients, 5) Examining appropriate variations in chemistry and their effect on signal evolution, and 6) Exploring the thermodynamics of the relaxation processes with respect to pore size by freezing the material during hydration.The proposed activity will expand our understanding of the chemical state of water in hydrating cement and provide a foundation for using TDR spectroscopy as a powerful tool for investigating hydration in a variety of cementitious materials. Results will have applications in a variety of inorganic/organic systems including the study of structure and dynamics in aqueous and biological systems including DNA, proteins, and micelles. The activity will impact on our collaboration with industry in process-monitoring and control and our involvement with students through undergraduate research at Elizabethtown College. It could lead to long-term collaboration with our biology department on potential biological applications and development of a business project for cement sensors through our business department.

我们实验室先前的工作证明了在10 kHz至8 GHz的频率范围内，从初始混合到几周固化，对水合波特兰水泥中的介电弛豫谱进行连续监测。 测量使用宽带时域反射介电谱与35 ps的刺激和嵌入式电容传感器。三个基本信号被确定，对应于未反应的自由水，结合水附着在发展中的微观结构，和晶粒极化。将三个信号分量作为固化时间的函数拟合到适当的分子模型，并在整个过程中进行监测。结果是1）自由水弛豫，其监测水在水合作用中的消失，因此遵循百分比水合作用，和2）结合水弛豫，其监测水附着到发展的微结构上，因此监测该微结构的形成，和3）谷物-极化弛豫监测这种微结构的发展。拟议的研究现在将扩大这一调查，严格比较信号变化通过分析测量、化学变化和实验研究的组合，在每个组件中发生化学和材料变化。测量可以包括但不限于：差示扫描量热法（DSC）、热重分析（TGA）、热孔隙度测定法、准弹性中子散射（QENS）、光学显微镜和标准机械压缩强度测试。具体的任务包括1）将测量分辨率扩展到接近10 GHz以更好地分辨各个游离水和结合水组分，2）将接近10 GHz的游离水的消失与通过DSC和热重分析确定的水合增加相关联，3）将接近100 MHz的结合水的增加与通过QENS、显微镜、和其它方法，4）通过在不同深度处用传感器测量大型测试圆柱体并确定水分梯度来估计蒸发的自由水损失，5）检查化学的适当变化及其对信号演变的影响，（六）通过在水化过程中冻结材料，探索松弛过程与孔径大小相关的热力学。我们的水化水泥中的水的化学状态的理解，并提供了一个基础，使用TDR光谱作为一个强大的工具，调查在各种胶凝材料的水化。结果将在各种无机/有机系统中应用，包括在水和生物系统，包括DNA，蛋白质和胶束的结构和动力学的研究。该活动将影响我们与工业界在过程监测和控制方面的合作，以及我们通过伊丽莎白敦学院的本科研究与学生的参与。这可能导致与我们的生物部门就潜在的生物应用进行长期合作，并通过我们的业务部门开发水泥传感器的业务项目。