Transport Kinetics of Internal Curing Water in High Performance Concretes

随着低水灰比高性能混凝土和硅灰的出现，早期开裂的发生频率越来越高。自干收缩和混凝土内部相对湿度的降低已被确定为高性能混凝土过早开裂和耐久性问题的主要原因。然而，高性能混凝土越来越多地用于更恶劣的环境中，导致对减缓自收缩的需求增加。内部固化材料可以有效地减少早期收缩。然而，人们对减缓收缩的潜在机制了解甚少。本研究计划旨在回答几个悬而未决的问题，这些问题必须在结构混凝土中常用的内部养护材料之前解决。迄今为止，缺乏关于在自干燥过程中通过胶凝微观结构携带水分运输的实验数据，限制了对内部固化机制的理解。为了改善目前关于内部固化的水分传输动力学的知识状态，本研究计划提出应用新的原位微结构表征技术（其中一些尚未应用于水泥基材料）来观察水分通过多孔胶凝基质的运动，而不会引入人工制品或损坏样品。应用的技术包括：(1)傅里叶变换红外（FTIR）光谱，(2)拉曼光谱，(3)1H核磁共振(NMR) / 1H核磁共振成像（MRI）。FTIR和拉曼光谱将用于定量和定位水化水泥浆和砂浆中的水。这些测绘和监测水泥基材料分布的新技术以前没有被探索过，尽管它们具有明显的潜力。结合这些技术，1H NMR T2弛豫时间分析和1H NMR成像（MRI）将用于分析水如何在水泥基体中结合，并阐明水的流动性。从这三种原位表征技术中收集的数据汇总将为流体通过水泥基材料的运动动力学提供前所未有的视角，并将有助于提高对各种内部固化材料有效性的理解。将开发连续介质计算模型来补充微观结构研究。除了表征和建模之外，自收缩、流变、强度和耐久性的物理测试将提供对内部固化材料对建筑实践中使用的混凝土的影响的透彻理解。在这个研究项目中收集的数据将为工程师提供内部固化材料实际使用的知识。此外，有关水分输送动力学的信息可以应用于许多混凝土耐久性问题，如氯化物的侵入。将开发教育模块，向初高中学生介绍土木与环境工程的各个学科，向小学学生介绍科学与工程。

Abstract 0556015With the advent of high performance concrete containing low water-to-cement ratios and typically silica fume, early age cracking has occurred with greater frequency. Autogenous shrinkage due to self-desiccation and the lowering of the internal relative humidity of concrete has been established as the primary cause of premature high performance concrete cracking and durability concerns. However, high performance concretes are increasingly used in more hostile environments, leading to an increased need for the mitigation of autogenous shrinkage. Internal curing materials can be effective for minimizing early age shrinkage. However, the underlying mechanisms of shrinkage mitigation are poorly understood. This research plan aims to answer several outstanding questions that must be addressed prior to internal curing materials being commonly used in structural concrete. To date, the lack of experimental data concerning entrained water moisture transport through a cementitious microstructure during self-desiccation has limited the understanding of the mechanisms of internal curing. To improve the current knowledge state regarding the moisture transport kinetics of internal curing, this research plan proposes the application of novel in situ microstructural characterization techniques (some of which have not been applied to cement-based materials for this purpose) to observe moisture movement through a porous cementitious matrix without introducing artifacts or damaging the sample. The techniques to be applied include: (1) Fourier Transform Infrared (FTIR) spectroscopy, (2) Raman spectroscopy, and (3) 1H Nuclear Magnetic Resonance (NMR) / 1H NMR Imaging (MRI). FTIR and Raman spectroscopy will be used to quantify and locate water in hydrating cement pastes and mortars. These novel techniques for mapping and monitoring the distribution in cement-based materials have not been previously explored, despite their obvious potential. Used in conjunction with these techniques, 1H NMR T2 relaxation time analysis and 1H NMR imaging (MRI) will be used to analyze how the water is bound within the cement matrix and the mobility of this water will be elucidated. The summation of data collected from these three in situ characterization techniques will provide an unprecedented view of the kinetics of fluid movement through cement-based materials and will lead to an improved understanding of the effectiveness of the various internal curing materials. A continuum computational model will be developed to complement the microstructural research. In addition to the characterization and modeling, physical testing of autogenous shrinkage, rheology, strength, and durability will provide a thorough understanding of the impact of internal curing materials on concretes to be used in construction practice. Data collected during this research program will provide engineers with the knowledge for practical use of internal curing materials. Furthermore, information regarding moisture transport kinetics can be applied to numerous concrete durability problems, such as chloride ingress. Educational modules will be developed to introduce middle and high school students to the various disciplines in Civil and Environmental Engineering and primary grade students to science and engineering.