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

我们实验室之前的工作表明，从初始搅拌到几周养护，连续监测水化波特兰水泥的介电弛豫谱的频率范围为10 kHz至8 GHz。测量采用宽频域反射介电谱，激励电压为35ps，内置电容传感器。确定了三个基本信号，分别对应于未反应的自由水、附着在发育中的微结构上的束缚水和颗粒极化。作为固化时间的函数，这三个信号分量适合适当的分子模型，并在整个过程中进行监测。其结果是1)自由水松弛，它监测水在水化过程中的消失，从而跟踪水化百分比；2)束缚水松弛，它监视附着在发展中的微结构上的水，从而监视这种微结构的形成；以及3)颗粒极化松弛，它监视这种微结构的发展。现在，拟议的研究将扩展这项研究，通过分析测量、化学变化和实验研究的结合，严格比较每个组分中发生的信号变化和化学和材料的变化。测量可能包括但不限于：差示扫描量热仪(DSC)、热重分析(TGA)、热孔度计、准弹性中子散射(QENS)、光学显微镜和标准机械抗压强度测试。具体任务包括：1)将测量分辨率扩展到接近10 GHz，以更好地解析单个自由水和束缚水成分；2)将10 GHz附近自由水的消失与DSC和热重分析所确定的水合增加相关联；3)将100 MHz附近束缚水的增加与QENS、显微镜和其他方法所确定的反应产物的形成相关联；4)通过在不同深度用传感器测量大型测试圆柱体并确定水分梯度，来估计由于蒸发造成的自由水损失；5)检查化学中的适当变化及其对信号演变的影响，6)通过在水化过程中冻结材料来探索与孔大小有关的松弛过程的热力学，所提出的活动将扩大我们对水化水泥中水的化学状态的理解，并为利用TDR光谱作为一种强有力的工具来研究各种胶凝材料的水化作用提供基础。这些结果将在各种无机/有机体系中得到应用，包括研究水和生物体系中的结构和动力学，包括DNA、蛋白质和胶束。这项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大学本科生研究与学生的接触。这可能会导致与我们的生物部就潜在的生物应用进行长期合作，并通过我们的业务部开发水泥传感器的商业项目。

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.