Concrete is the most consumed manufactured commodity by mass in the world. The manufacturing of Portland cement, the binder of modern concrete, is responsible for 8-9% of global anthropogenic carbon dioxide (CO2) emission, and 2-3% of primary energy consumption. Study of green cement and concrete can provide efficient solutions to reduce the environmental burden of this commodity in the construction industry.

Most concrete is produced using calcium silicate hydrate (C-S-H)-based binder. Understanding the structure of C-S-H based phases is essential to designing a more sustainable cement and concrete. Dicalcium silicate (C2S) is a common clinker compound in both Portland cement and belite-ye’elimite-ferrite cement. The formation of C2S is less energy intensive and yields less CO2. C-S-H is the primary hydration product in hydrated C2S. Incorporation of aluminum-rich industrial by-product is a common method to reduce the environmental impact of concrete production, the principal binding phase of this blended cement-based concrete is calcium aluminosilicate hydrate (C-A-S-H). Sodium hydroxide and sodium silicate activated ground granulated blast-furnace slag are promising cementitious materials alternative to Portland cement due to their lower CO2 emission, the principal binding phase in these alkali-activated materials is sodium incorporated calcium aluminosilicate hydrate (C-N-A-S-H).

This thesis aims to understand different calcium (alumino)silicate hydrates at multi-scale. The characterization of C-S-H and its derivatives, C-A-S-H and sodium incorporated calcium (alumino) silicate hydrate (C-N-(A-)S-H), is reported. There are three main gaps in the current state-of-the art that need to be investigated: (1) β-C2S is the most common C2S polymorph in cement, yet the hydration of other polymorphs (e.g., α’H-C2S ) has rarely been studied, the molecular structure of C-S-H in hydrated α’H-C2S has not been reported; (2) the structure of synthetic C-S-H has extensively studied, however the influences of aluminum incorporation on the coordination environment of Ca and Si in C-A-S-H have not been well understood; (3) the influences of calcium to silicate molar ratio and aluminum induced cross-linking sites on the nanomechanical properties C-S-H have been understood. However, the molecular structure and influence of sodium incorporation of nanomechanical properties of C-N-(A-)S-H have not been resolved.

The studies described in this thesis uses synchrotron radiation-based X-ray techniques to provide new information of the above-mentioned questions. X-ray spectromicroscopy coupled with soft X-ray ptychographic imaging is used to compare the hydration of two polymorphs of dicalcium silicate (β-C2S and α’H-C2S) and to determine the structure of hydration product C-S-H at atomic to microscale. The coordination environments of Ca and Si of C-S-H in the hydrated C2S are studied. Wide-angle X-ray scattering, X-ray spectromicroscopy, and soft X-ray ptychographic imaging are utilized to investigate the atomic to micro-structure of C-S-H and C-A-S-H. The influences of Ca/Si and Al/Si ratios on the coordination chemistry and morphology of C-A-S-H are investigated. High-pressure X-ray diffraction is used to investigate the anisotropic mechanical properties of sodium incorporate C-S-H and C-A-S-H.

The experimental results indicated that C-S-H formed in hydrated β-C2S and α’H-C2S exhibited similar coordination symmetry of Ca. The silicate chains of C-S-H formed in hydrated α’H-C2S polymerize faster than those in hydrated β-C2S. The aluminum incorporation has no significant influences on the coordination symmetry of Ca of synthetic C-S-Hs, while aluminum incorporation increases their silicate polymerization. The morphology of synthetic C-(A-)S-Hs at the nanoscale is independent of the aluminum incorporation and their Ca/Si ratio at temperature of 7-50 °C. The foil of C-A-S-H is significantly coarser at synthesis temperature of 80 °C. Under hydrostatic pressure up to ~10 GPa, the sodium incorporated C-A-S-H exhibit significantly higher incompressibility along the c-axis than sodium incorporated C-S-H and alkali-free C-A-S-H along the c-axis. The experimental results in this thesis improve the understanding of the chemistry of C-S-H and its derivatives (C-A-S-H and C-N-(A-)S-H). The work is important for providing evidence to design high-performance C-S-H based concrete using a bottom-up approach.

Seismic anisotropy is now commonly studied on Earth and has been detected at various depths, from the crust to the top of the lower mantle, in the lowermost mantle, and in the inner core. In the mantle, observations of seismic anisotropy are often taken as an indication of past or present deformation resulting in the preferential orientation of anisotropic minerals. In the crust, it can come from stress-induced oriented cracks, compositional layering, or crystallographic preferred orientation of minerals. 

While many questions remain regarding the presence and interpretation of seismic anisotropy on Earth, scientists are now faced with new, exciting challenges in trying to constrain the structure of other planetary bodies. One of the goals of NASA’s InSight mission, which landed on Mars in November 2018 and includes a very broadband seismometer, is to constrain Mars interior structure. Compared to seismic studies of Earth, which benefit from the availability of a wealth of high quality data recorded on many seismic stations, difficulties with InSight stem from having only one seismic instrument and only a few high quality events. 

In this study, we analyzed the horizontally polarized (SH)-wave reflections generated from the shallowest crustal layer (layer 1) detected at 8 ± 2 km beneath the InSight lander site by a previous receiver function (RF) study. From Sol 105, when the first low-frequency marsquake was recorded, to Sol 1094, a total of 83 broadband and low-frequency events were detected, but only nine are rated as quality-A with constraints on both their epicentral distance and back azimuth. Of those nine events, we selected four that did not show any interference with mantle triplications generated by the olivine to the wadsleyite phase transition and that had a clear signal after the direct SH phase. A model space search approach enabled us to obtain a range of acceptable SH-wave velocities and layer thicknesses, which we then compared with the RF models of Knapmeyer-Endrun et al. (2021). We found that the acceptable SH-wave speeds are systematically lower than those from the RF study. Since this RF analysis is sensitive to vertically polarized (SV)-waves, we interpret this difference as the signature of radial anisotropy with an anisotropy coefficient ?=(?_??/?_??)² between 0.7 and 0.9. Modeling of preferred alignment of inclusions shows that dry or fluid-filled cracks/fractures, and igneous inclusions can reproduce the observed radial anisotropy amplitude with V_SV>V_SH.