SusChEM: Environmentally sustainable concretes enabled by multiscale investigation of ancient Roman concretes

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NON-TECHNICAL DESCRIPTION: Production of concrete based on Portland cement hydration is an energy intensive process responsible for a staggering 5-8% of the annual global CO2 emissions. The concretes of ancient Roman monuments and seawater harbors, produced from volcanic rocks and hydrated lime, have a far smaller CO2 footprint than conventional Portland cement concretes, far greater chemical and mechanical resistance to decay, and take a smaller energy budget to produce. The secret to the environmental sustainability of the 2000-year old concretes is traced to the chemical nature of the mortar binder. The goal of the project is to gain a fundamental understanding of this chemistry. The broader impact of this work lies in its positive contributions to interdisciplinary science, society, and educational and outreach activities. The research will provide guideposts for greater sustainability of our resources (both energy and clean water) and future applications to high performance concretes, as well as to increased durability of Portland cement concretes blended with environmentally-friendly supplemental materials, and including seawater, which conserves fresh water resources. From a societal perspective, the research has the potential to transform traditional concepts of the concrete industry based on Portland cement hydration, to binding mechanisms inherent in naturally-occurring volcanic ash deposits. The results may also be of value in developing improved methods for conservation of ancient structures and more recent concrete structures. From an economic perspective, it will contribute to "green" construction, an important growth sector of the national economy. TECHNICAL DESCRIPTION: This project aims to gain a fundamental understanding of the hydration mechanisms, binding mechanisms, cation exchange properties, and nanoscale mechanical properties of 2000-year old cementitious components of Roman concretes. The research is based on a nanostructural approach that focusses on thin, intact slices of mortars, already prepared from the Baianus Sinus breakwater (first century BC) in Pozzuoli Bay near Naples, Italy, and reproductions of these materials prepared with Campi Flegrei volcanic ash. The primary analytical techniques include X-ray microdiffraction (to identify crystalline phases), Raman spectroscopy (for structural and vibrational properties and bonding environment characterization), nuclear magnetic resonance (for Si-O and Al-O bonding environments), high-resolution transmission electron microscopy (for detailed nanostructural studies), nanoindentation to assess mechanical properties of these phases (modulus, hardness, strength) with nanoscale resolution, and engineering strength and durability testing for the mortar reproductions. It is anticipated that this research will result in new formulations of high performance concretes with a lifetime improvement of over one order of magnitude, and in new processes designed specifically for reduced waste product, especially CO2 emissions, and for much higher energy efficiency than current processes. A significant impact of this project is in education, in particular by training graduate and undergraduate students in several disciplinary areas: materials science, earth science, archaeological science, and civil engineering.