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

我们实验室之前的工作证明了水化波特兰水泥的介电弛豫谱在10 kHz至8 GHz频率范围内的连续监测，从最初的混合到几周的固化。测量采用宽带时域反射电介质光谱法，外加35ps刺激和内嵌电容传感器。确定了三个基本信号，分别是未反应的自由水、附着在发育微观结构上的结合水和晶粒极化。这三种信号成分作为固化时间的函数适合于适当的分子模型，并在整个过程中进行监测。结果是：1)自由水弛豫监测水在水化过程中的消失，从而跟踪水化百分比；2)结合水弛豫监测水附着在发育中的微观结构上，从而监测该微观结构的形成；3)晶粒极化弛豫监测该微观结构的发育。拟议的研究现在将扩展这一调查，通过分析测量、化学变化和实验调查的结合，严格比较每个成分中发生的信号变化与化学和材料变化。测量可能包括但不限于：差示扫描量热法（DSC）、热重分析（TGA）、热量法、准弹性中子散射（QENS）、光学显微镜和标准机械压缩强度测试。具体任务包括：1)将测量分辨率扩展到10 GHz附近，以更好地分辨单个自由水和结合水成分；2)通过DSC和热重分析将10 GHz附近自由水的消失与水化的增加联系起来；3)通过QENS、显微镜和其他方法将100 MHz附近结合水的增加与反应产物的形成联系起来。4)通过在不同深度安装传感器的大型测试筒，确定水分梯度，估算自由水分蒸发损失；5)检查适当的化学变化及其对信号演化的影响；6)在水化过程中，通过冻结材料，探索与孔径有关的松弛过程的热力学。所提出的活性将扩大我们对水化水泥中水的化学状态的理解，并为使用TDR光谱作为研究各种胶凝材料水化的有力工具奠定基础。结果将应用于各种无机/有机系统，包括水系统和生物系统的结构和动力学研究，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镇学院的本科生研究与学生的合作。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。

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.