Using Additive Manufacturing to Enhance Carbonation Rates of Magnesium Silicate Binders

Abstract

The concrete and cement industry contributes to around 7-8% of global anthropogenic carbon emissions. This thesis investigates using a magnesium silicate binder as a potential replacement for ordinary portland cement (OPC), which would sequester carbon dioxide to form a magnesium carbonate-based cement. Other carbonation-based binders including calcium silicates and reactive magnesium oxide have been studied but present significant cost barriers. Magnesium silicates, especially in the form of the mineral olivine, are highly prevalent in the Earth's crust. However, olivine faces low dissolution and carbonation rates. This thesis explores whether additive manufacturing (AM) combined with an ex-situ carbonation approach can increase carbonation rates. This work develops a magnesium silicate binder suitable for 3D printing via flow table analysis, miniature slump cone tests, and rheometry. X-ray diffraction is used to characterize the raw material and the finalized mix in an uncarbonated and carbonated state. Cast and 3D-printed samples were placed in a carbonation chamber and tested using thermogravimetric analysis to examine the extent of carbonation. Finally, three-point bending is utilized to investigate the mechanical properties of the samples. Preliminary findings indicate that an ex-situ approach achieves a limited extent of carbonation. However, between the cast, lamellar, and cellular sample types tested, cellular 3D-printed samples achieved higher extents of carbonation in their interior cross-section. Thus, materials architecture and additive manufacturing could inform the refinement of this research. Future research includes exploring using an in-situ carbonation approach or a pH swing procedure to increase carbonation rates in combination with additive manufacturing.