Mechanisms and Mitigation of Shrinkage and Carbonation in Alkali-Activated Concrete

碱激发混凝土（AACs）是传统波特兰水泥混凝土的有前途的绿色替代品，因为它们提供显著的能量和CO2节约，这是由于用工业废料完全（100%）替代波特兰水泥。然而，这些材料尚未得到广泛的行业接受，主要是由于其不确定的长期耐久性性能，对收缩/开裂，碳酸化/腐蚀，和碱骨料反应。这项工作的目标是（1）推进的原因和机制的收缩和碳化的AAC在多个长度尺度的知识，（2）利用这些新的知识，提出和评估有效的缓解策略，以促进生产高性能AAC材料。三个主要的碱激活粘合剂具有极大的不同组合物将进行研究;富钙炉渣为基础的AAC，铝丰富的F类粉煤灰为基础的AAC，和复合矿渣粉煤灰粘合剂，含有中等水平的钙和铝。一种新的研究方法，提出了宏观尺度的收缩和碳化性能定量链接到材料？的微观结构和特定相的成分和性能。该方法基于集成先进的表征技术（例如，FIB、纳米压痕、NMR、SEM/EDS/ QXRD）和面向对象的FEM模拟;并允许确定最佳材料配比和加工实践，从而实现稳定的相形成，降低收缩和碳酸化的风险，而不影响强度和其他性能要求。此外，化学形态模拟可用于设计新型外加剂以减少碳化和诱导膨胀反应，研究成果对改善碱激发混凝土以及波特兰水泥和其他替代混凝土材料的性能极为有益。该研究与教育计划，包括（a）推广，招聘和保留女性和少数民族学生在土木工程教育，研究和职业，和（B）提供了一个世界一流的研究和教学经验的研究生和本科生。此外，这项工作将有助于工程教育文献，通过开发主动学习和创新的以学生为中心的教学方法，并评估这些方法在提高学生的学习，参与和保留的有效性。

Alkali activated concretes (AACs) are promising green alternatives to conventional portland cement concrete, as they offer significant energy and CO2 savings that results from full (100%) replacement of portland cement with industrial waste products. However, these materials have not yet received broad industry acceptance, primarily due to their uncertain long-term durability performance against shrinkage/cracking, carbonation/corrosion, and alkali-aggregate reaction. The objectives of this work are to (1) advance the knowledge on the causes and mechanisms of shrinkage and carbonation of AACs at multiple length-scales, and (2) utilize this new knowledge to propose and evaluate effective mitigation strategies to promote production of high performance AAC materials. Three main alkali activated binders with vastly different compositions will be studied; a Ca-rich slag-based AAC, an Al-rich class F fly ash-based AAC, and a composite slag-fly ash binder, containing moderate levels of both Ca and Al. A novel research approach is proposed where the macro-scale shrinkage and carbonation performance is quantitatively linked to the material?s microstructure and phase-specific compositions and properties. This approach is based on integrating advanced characterization techniques (e.g., FIB, nano-indentation, NMR, SEM/EDS/ QXRD) with object oriented FEM simulations; and allows identifying the optimum material proportioning and processing practices that result in stable phase formation, and low risk of shrinkage and carbonation, without compromising strength and other performance requirements. In addition, chemical speciation modeling is used to design novel admixtures to reduce carbonation and to induce expansive reactions.The research outcomes can be extremely beneficial towards improving the performance of alkali activated concretes, as well as portland cement and other alternative concrete materials. The research is well integrated with educational plans, including (a) outreach, recruitment, and retention of female and minority students in civil engineering education, research, and careers, and (b) providing a world-class research and teaching experience for graduate and undergraduate students. In addition, this work will contribute to engineering education literature by developing active learning and innovative student-centered instructional methods, and assessing the effectiveness of such methods in improving learning, engagement, and retention of students.