Characterization of Damage and Development of Accelerated Test Method for Delayed Ettringite Formation

混凝土中一个潜在的严重劣化问题与钙矾石形成延迟(DEF)有关。这种破坏通常被认为是材料内部类似于碱-硅酸盐反应(ASR)的膨胀过程的结果，但这种过程的许多方面仍然存在争议。需要改进与DEF相关的损伤特征，以更好地了解所涉及的具体机制，并开发更好的预测失败的模型。该项目的主要目标包括使用尖端技术来理清构成膨胀混凝土裂缝复杂过程的具体破坏机制。这反过来将导致更可靠的DEF预测模型和更准确的加速试验方法，这些方法将作为建议更改混凝土搅拌和养护的规范和/或实践的基础，以防止这一问题。具体地说，这项研究将调查钙矾石的形成、钙矾石分布、微裂纹分布和体积变化之间的相关性。该项目将实施的先进技术，包括同步辐射衍射、激光剪切成像和工业X射线计算机层析成像，在这一领域的研究是相当新颖的。这些数据将使用材料科学理论进行分析，包括成核和生长动力学以及损伤力学。拟议的活动将为这些先进技术在混凝土等材料中的应用提供新的见解。对现有的、改进的和拟议的快速试验方法进行的广泛评估将有助于开发一种有用的标准试验方法来评估混凝土的长期尺寸稳定性和耐久性。拟议研究的这些贡献将是重大的，因为水泥和混凝土的ASTM规范中没有解决DEF的问题。没有标准的测试可用，也没有对水泥的化学成分设定任何限制来控制DEF。此外，开发一种快速测试方法的提议如果成功将产生重大影响，因为需要评估混凝土中DEF的有害影响是当今研究人员面临的最重要的问题之一。这一项目对国家公路和桥梁系统以及整个民用基础设施的益处将是巨大的。拟议的项目将加强马里兰大学、FHWA和NIST之间的现有合作伙伴关系，并将有助于与密歇根大学、霍华德大学和激光技术公司建立新的合作伙伴关系。研究团队将从与该领域知名专家、FHWA基础设施研发办公室高级物理科学家理查德·A·利文斯顿博士的合作中受益匪浅。这些伙伴关系将极大地加强马里兰大学本科生和研究生的研究和教育基础设施。该项目将得到麦克奈尔计划等项目的资金补充，以确保代表人数不足的学生和妇女参与其中，这将包括有才华的本科生。

A potentially serious deterioration problem in concrete is associated with delayed ettringite formation (DEF). This damage is typically viewed as the result of an expansive process within the material similar to that of alkali-silicate reaction (ASR), but many aspects of this process remain controversial. Improvements in the characterization of damage associated with DEF are needed both to gain a better understanding of the specific mechanisms involved and to develop better models for predicting failure. The main objectives of this project include the use of cutting edge technology to sort out the specific damage mechanisms that make up the complex process of expansive concrete cracking. This in turn will lead to more reliable predictive models of DEF and to more accurate accelerated test methods that will serve as the basis for recommendations for changes in specifications and /or practices of mixing and curing concrete to prevent this problem. Specifically the study will investigate the correlations between ettringite formation, ettringite distribution, microcrack distributions and volumetric change. The advanced technologies that are to be implemented in this project, including synchrotron radiation diffraction, laser shearography and industrial X-ray computed tomography are fairly novel to research in this area. The data will be analyzed using material science theory including nucleation and growth kinetics and damage mechanics. The proposed activities will provide new insights into the application of these advanced technologies for materials such as concrete. The proposed extensive evaluations of existing, improved and proposed rapid test methods will contribute to the development of a useful standard test method to assess long-term dimensional stability and durability of concrete. These contributions by the proposed study would be significant since the problem of DEF has not been addressed in ASTM specifications for cement and concrete. No standard tests are available and no limits on the chemical composition of cements to control DEF have been set. Also the proposal to develop a rapid test method if successful would have significant impact since the need to assess the deleterious effects due to DEF in concrete is one of the most important issues facing researchers today. The benefits of this project to the nations highway and bridge systems and to civil infrastructures in general will be significant. The proposed project will strengthen existing partnerships between University of Maryland, FHWA and NIST, and would help establish new partnerships with University of Michigan, Howard University, and Laser Technologies, Inc. The research team will greatly benefit from collaboration with well-known specialist in the field, Dr. Richard A. Livingston, Senior Physical Scientist, Office of Infrastructure R&D, FHWA. These partnerships will greatly enhance the infrastructure for research and education for undergraduate and graduate students at University of Maryland. This project will be supplemented with funds from programs such as the McNair program to ensure the participation of underrepresented students and women and this would include talented undergraduate students.