Collaborative Research: Discovering Precipitation Pathways in Reactive Magnesium Oxide Cements via Nanoscale Interfacial Engineering for Durable Structural Composites

这项合作研究的重点是研究和发现具有强大机械性能的氧化镁基水泥材料，用于民用基础设施的可持续建设。活性氧化镁水泥（RMC）作为一种现代混凝土粘结剂，是替代普通硅酸盐水泥的最有前途和最环保的材料之一。与传统水泥相比，RMC的优势包括低成本和低碳足迹。RMC通过与二氧化碳和水反应形成不同的碳酸镁相作为结合力来获得其强度。然而，现有rmc的强度和耐久性表现出显著的变化，减缓了它们在建筑行业的采用。本研究将解决以下两个技术挑战：(i)利用新颖的实验测试和计算机模拟来理解控制致密碳酸镁相形成的基本过程；（ii）通过加入耐腐蚀的微纤维和宏纤维，创新耐用的高强度rmc基复合材料。在该项目中，将为K-12，本科生和研究生实施外展计划，以传播建筑行业低碳结构材料的知识，并培养具有可持续基础设施工程背景的下一代学生和工程师。本研究的主要目标是通过操纵热力学和动力学沉淀途径来定制活性氧化镁水泥的碳化产物，以获得高性能的rmc基复合材料。RMC可以通过低温（500-1000°C）煅烧菱镁矿矿床或废盐水中的水镁石沉淀来生产。因此，它被认为是一种比普通波特兰水泥更可持续的粘合剂，后者的生产占全球人为二氧化碳排放量的7%。然而，RMC不同反应产物的比容变化较大，且由于钝化氧化层的缺失或快速损失，埋入钢筋容易受到腐蚀，阻碍了其在建筑实践中的广泛应用。为了解决这些长期存在的挑战，本研究提供了一个结合实验和计算的研究计划，有两个目标：(i)通过与非反应性种子（石英、方解石、菱镁矿和白云石）的纳米级界面能考虑来指导成核和生长途径，以避免低密度水合碳酸镁相的沉淀，从而通过调节热力学和动力学驱动力之间的竞争来减少体积变化；（ii）利用这些基本知识开发致密的rmc基纤维增强结构复合材料，这种复合材料渗透性较低，更耐开裂和腐蚀。这种方法利用纳米尺度的成核和生长过程的基本原理，而不是对不同的混合设计和加工条件进行逐个测试，以实现强大的复合材料性能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This collaborative research is focused on investigating and discovering magnesium oxide-based cement materials with strong mechanical properties for sustainable construction of civil infrastructure. Reactive magnesium oxide cement (RMC) is one of the most promising and environmentally friendly alternatives to ordinary Portland cement as a modern concrete binder. The advantages of RMC include low-cost and low carbon footprint compared to conventional cements. RMC achieves its strength by forming different magnesium carbonate phases as binding agents by reacting with carbon dioxide and water. However, the strength and durability properties of existing RMCs exhibit significant variations, slowing their adoption by construction industry. This research will address the following two technical challenges: (i) understanding the fundamental processes that govern the formation of dense magnesium carbonate phases using novel experimental testing and computer simulation; and (ii) innovation of durable RMC-based composites with high strength by incorporating corrosion-resistant micro- and macro-fibers. In this project, an outreach program for K-12, undergraduate, and graduate students will be implemented in order to disseminate knowledge on low-carbon structural materials for the construction industry, and train next generation students and engineers with sustainable infrastructure engineering backgrounds. The primary goal of this research is to tailor the carbonation products of reactive magnesium oxide cement by maneuvering thermodynamic and kinetic precipitation pathways in order to achieve high-performance RMC-based composites. RMC can be produced from low-temperature (500-1000 °C) calcination of either magnesite deposits or brucite precipitates from reject brine. Thus, it is deemed a more sustainable binder to ordinary Portland cement, whose production accounts for 7% of the global anthropogenic carbon dioxide emissions. Yet, the large specific volume variability of the different reaction products of RMC and the vulnerability of the embedded rebars to corrosion due to an absence or quick loss of the passivating oxide layer hindered its widespread application in the construction practice. To address these longstanding challenges, this research offers a combined experimental and computational research plan with two objectives: (i) to guide the nucleation and growth pathways via nanoscale interfacial energy considerations with non-reactive seeds (quartz, calcite, magnesite, and dolomite) to avoid the precipitation of low-density hydrated magnesium carbonate phases and hence reducing the volume change by modulating the competition between thermodynamics and kinetics driving forces, and (ii) to employ this fundamental knowledge to develop dense RMC-based fiber-reinforced structural composites that are less permeable and more resistant to cracking and corrosion. This approach exploits the fundamentals of the nucleation and growth process at the nanoscale, rather than case-by-case testing of different mix designs and processing conditions, to achieve robust composite performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.