Characterizing the reactivity and industrial ecology of pseudowollastonite to enable highperformance building materials from waste streams

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Ordinary Portland cement is a critical building material with a large environmental footprint. Preliminary work carried out by the investigator's group suggests that an alternative material, pseudowollastonite (PWOL), which is a high temperature polymorph of calcium silicate (CaSiO3), can form a variety of platey mineral products during hydration and carbonation. It appears that these products resemble the mineral phases that give ancient Roman cement much of its strength and its remarkable ability to gain strength over time even in environments that would rapidly degrade modern cements. Also, there is reason to anticipate that substituting one or more of these products for Portland cement may lead to a decreased environmental footprint. However, a large number of questions exist as to which combination of reactions and chemical conditions result in the formation of these phases. This project will develop both the physicochemical understanding needed to deploy PWOL-based cements and the systems-level life cycle and techno-economic potential of deploying these types of materials in an economically competitive and sustainable manner. The work is divided into four research tasks-- Task 1. Characterize the chemical kinetics of PWOL carbonation and hydration under a range of natural water and atmospheric conditions. Task 2. Evaluate the chemical stability of the resulting mineral phases. Task 3. Measure the mechanical strength of PWOL cements. Task 4. Understand the Industrial Ecology of PWOL cements. This work will include fundamental advances in the understanding of aqueous carbonation of PWOL at high temperatures. Preliminary experiments suggest that PWOL reacts very differently with CO2, H2O, and Na+ than wollastonite, which is already being actively developed as a carbon neutral cement alternative. The products of PWOL reactions will be tested for their chemical stability and mechanical strength under a range of representative conditions. In parallel, the industrial ecology of PWOL-based cements will be studied to evaluate both the economic opportunity and environmental implications of this cement substitute. PWOL is relatively uncommon in nature but abundant in industrial waste streams such as cement kiln dust. It is also possible that it could be synthesized using other waste streams using less energy than it takes to make ordinary Portland cement. The curing of these materials, which require heat, moisture andCO2, could occur in the presence of a flue gas stream, and so a geospatial analysis will be carried out to understand where in the United States these waste streams are in close proximity. Efforts to develop carbon capture, utilization, and storage (CCUS) technologies, like the one proposed here, are motivated in part by the goal of reducing net emissions of greenhouse gas. Quantifying those emissions can be challenging, especially for innovative technologies. To support greater transparency in pursuing CCUS activities, this project will develop guidelines and an open-source tool for evaluating the life cycle performance of CCUS projects in the concrete alternatives space. Such an effort can serve as a model for other CCUS applications areas to help promote transparency and rapid assessment of early-stage CCUS ventures.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.