Transport Kinetics of Internal Curing Water in High Performance Concretes

高性能混凝土内养护水的传输动力学

• 批准号: 0556015
• 负责人: Benjamin Mohr
• 金额: $ 22.08万
• 依托单位: Tennessee Technological University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0556015&HistoricalAwards=false
• 关键词: Transport; Kinetics; Internal; Curing; Water

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.

摘要0556015随着含有低水灰比和典型的硅灰的高性能混凝土的出现，早期开裂以更高的频率发生。 由于自干燥和混凝土内部相对湿度的降低引起的自收缩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，导致对减轻自生收缩的需求增加。 内部固化材料可以有效地使早期收缩最小化。然而，收缩缓解的基本机制知之甚少。 本研究计划的目的是回答几个突出的问题，必须解决之前，内部固化材料通常用于结构混凝土。 迄今为止，由于缺乏有关自干燥过程中夹带水通过胶凝微结构传输的实验数据，限制了对内部固化机制的理解。 为了提高目前的知识状态关于内部固化的水分传输动力学，本研究计划提出了新的原位微观结构表征技术（其中一些尚未应用于水泥基材料，用于此目的）的应用，以观察水分运动通过多孔水泥基基质，而不引入文物或损坏样品。应用的技术包括：（1）傅里叶变换红外（FTIR）光谱，（2）拉曼光谱，和（3）1H核磁共振（NMR）/ 1H NMR成像（MRI）。 FTIR和拉曼光谱将用于量化和定位水化水泥浆体和砂浆中的水。 尽管这些用于绘制和监测水泥基材料分布的新技术具有明显的潜力，但之前尚未进行过探索。 结合这些技术，1H NMR T2弛豫时间分析和1H NMR成像（MRI）将用于分析水如何结合在水泥基质中，并阐明水的流动性。 从这三种原位表征技术收集的数据的总和将提供一个前所未有的观点，通过水泥基材料的流体运动的动力学，并将导致更好地理解各种内部固化材料的有效性。 一个连续计算模型将被开发，以补充微观结构的研究。 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施工实践中使用的混凝土的影响的透彻理解。 在这项研究计划中收集的数据将为工程师提供内部固化材料的实际使用知识。 此外，有关水分迁移动力学的信息可以应用于许多混凝土耐久性问题，如氯离子侵入。 将开发教育模块，向初中和高中学生介绍土木和环境工程的各个学科，向小学生介绍科学和工程。