Incorporating carbon sequestration materials in civil infrastructure: A micro and nano-structural analysis

The Calera method for carbon sequestration promotes carbon mineralization through aqueous precipitation. This work reports a comprehensive analysis on a carbonate obtained by the Calera process to evaluate its suitability as a cement replacement for concrete applications. This work focuses on the analysis of two hydrated cement pastes made with a blend of Portland cement and Calera carbonates by various advanced analytical techniques. Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) was used to observe microstructures and determine elemental compositions. The synchrotron X-ray diffraction technique combined with Rietveld analysis were applied to identify constituent phases and refine crystal structures, crystallite sizes as well as relative phase abundances. Calcite and vaterite are observed in all samples while CSH II and portlandite are dominant in the cement pastes. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectrometry and Scanning Transmission X-ray Microscopy (STXM) experiments were conducted to investigate chemical speciation and morphological information of carbonate minerals with different absorption energies. STXM results confirmed heterogeneity of the samples, and also provided a nano-scale phase map across multiple particles. Differential Thermogravimetric (DTG) was used to observe heat transfer through structures and changes in mass upon heating. A compressive strength tests were performed on materials and shown comparable strength to Portland cement.