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

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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.