Transport Kinetics of Internal Curing Water in High Performance Concretes

随着低水灰比、典型硅灰的高性能混凝土的出现，早期裂缝发生的频率越来越高。自干缩和混凝土内部相对湿度的降低是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被用于更恶劣的环境中，导致对减轻自收缩的需求增加。内部固化材料可以有效地将早期收缩降至最低。然而，缓解收缩的潜在机制却知之甚少。这项研究计划旨在回答在内部养护材料在结构混凝土中普遍使用之前必须解决的几个突出问题。到目前为止，缺乏关于自干燥过程中夹带水分通过胶凝微结构传输的实验数据，限制了对内部固化机理的了解。为了改善目前对内部养护水分迁移动力学的认识状况，本研究计划提出应用新的原位微结构表征技术(其中一些技术尚未应用于水泥基材料)来观察水分在多孔水泥基材中的迁移，而不会引入伪影或损坏样品。应用的技术包括：(1)傅里叶变换红外(FTIR)光谱，(2)拉曼光谱，(3)核磁共振(核磁共振)/核磁共振成像(MRI)。FTIR和拉曼光谱将被用来定量和定位水化水泥浆体和砂浆中的水。这些用于绘制和监测水泥基材料中分布的新技术以前从未被探索过，尽管它们具有明显的潜力。结合这些技术，将使用1H核磁共振T2弛豫时间分析和1H核磁共振成像(MRI)来分析水在水泥基质中的结合方式，并阐明水的流动性。这三种原位表征技术收集的数据的汇总将提供一个前所未有的视角来了解流体在水泥基材料中的运动动力学，并将导致对各种内部固化材料的有效性的更好理解。将开发一个连续介质计算模型来补充微观结构研究。除了表征和建模外，对自收缩、流变学、强度和耐久性的物理测试将使您彻底了解内部养护材料对施工实践中使用的混凝土的影响。在本研究计划期间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，有关水分传输动力学的信息可以应用于许多混凝土耐久性问题，例如氯离子进入。将开发教育模块，向初中和高中学生介绍土木工程和环境工程的各个学科，并向小学学生介绍科学和工程。

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.