X-Hab Reef: Sustainable Carbon-Neutral Materials for 3D-Printable Coastal Infrastructure

We propose to develop carbon-negative Magnesium Oxychloride Cement (“MOC”) material formulations incorporating novel bio-based products (i.e., hemp shives) and then verify the mechanical (i.e., compressive, and tensile strength), physical (i.e., length-change), and durability (i.e., leaching potential) properties of this novel material. With the goal of utilizing these materials for carbon-negative gray coastal infrastructure, this proposal leverages existing cutting-edge research on modern cement chemistry of research partners at The Pennsylvania State University to produce non-leaching, carbon-negative, and marine-compatible MOC reef starter structures.  The MOC chemical formulations to be investigated have been selected due to their compatibility with the marine environment. Recent research has demonstrated that, in high-salt aqueous environments such as seawater, the stability of phases composing MOCs is stable and, hence, minimal leaching has been reported. The selected MOC formulations proposed demonstrate the highest-marine compatibility with minimal leaching potential of various cement chemistry formulations.  While MgO cements have been used and researched before, our exploration of certain chemical formulations is unique and will lead to distinctive material properties (e.g., static yield stress, controlled setting time, tailored compressive strength) that can be scaled up in Phase II. The proposal circumvents CO2-process output and long-term durability challenges by building upon the team’s foundational research and novel exploration of Mg–Cl–S–Si with hemp shives MOC formulations. The addition of hemp shives (agricultural wastes from local hemp production) can offset calcination and sourcing CO2 emissions and result in a MOC material with negative CO2 emissions. A key aspect of this proposal is the development of economic-environmental lifecycle analysis tools for the optimal MOC formulations as well as the detailed investigation of the long-term marine durability of these materials.  In Phase II, a central composite design will be used to define the chemistry of the system that will be tailored towards 3D printing, where concrete is extruded from a nozzle and deposited digitally according to the designed printing toolpath to replace traditional techniques that require formwork and result in significant material waste and labor cost as well as higher associated embodied carbon and operational carbon emissions. Towards this goal, in addition to the comprehensive investigation of the mechanical, physical, and durability properties of MOCs, X-Hab 3D principal investigator, Nate Watson, will carry out the elementary investigation of the workability of MOCs. This preliminary investigation to control workability (primarily setting time of MOCs) is important to ensure that Phase II additive manufacturing goals can be achieved with desired rheological properties.