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

碱活化混凝土（AACs）是传统波特兰水泥混凝土的绿色替代品，因为它们可以完全（100%）替代波特兰水泥，从而节省大量能源和二氧化碳。然而，这些材料尚未得到广泛的工业认可，主要是由于它们在抗收缩/开裂、碳化/腐蚀和碱集料反应方面的长期耐久性不确定。这项工作的目标是：(1)推进对AAC在多个长度尺度上收缩和碳化的原因和机制的了解，(2)利用这些新知识来提出和评估有效的减缓策略，以促进高性能AAC材料的生产。研究了三种主要的碱活化粘合剂，它们的组成差别很大；富钙渣基AAC，富铝F类粉煤灰基AAC，以及含有适量Ca和Al的复合渣-粉煤灰粘结剂。提出了一种新的研究方法，其中宏观尺度的收缩和碳化性能与材料的定量联系在一起。S的显微组织和相组成及性能。该方法基于将先进的表征技术（例如，FIB，纳米压痕，NMR, SEM/EDS/ QXRD）与面向对象的FEM模拟相结合；并且可以确定最佳的材料比例和加工实践，从而实现稳定的相形成，降低收缩和碳化的风险，同时不影响强度和其他性能要求。此外，化学形态模型用于设计新的外加剂，以减少碳化和诱导膨胀反应。该研究成果对于提高碱活化混凝土的性能，以及波特兰水泥和其他替代混凝土材料都是非常有益的。这项研究与教育计划很好地结合在一起，包括(a)在土木工程教育、研究和职业中扩大、招聘和留住女性和少数族裔学生，以及(b)为研究生和本科生提供世界一流的研究和教学经验。此外，这项工作将通过开发主动学习和创新的以学生为中心的教学方法，以及评估这些方法在提高学生学习，参与和保留方面的有效性，为工程教育文献做出贡献。

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.