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.

In the next 28 years (2050), 68% of the world's population will reside in urban areas. This growth will increase the quantity and scale of infrastructure. Preceded only by water, concrete is the most used material by humankind and is part of most infrastructure, housing, and commercial projects. As a result, concrete is the fastest growing globally common structural material, and this will result in an increase in anthropogenic CO2 emissions, a greenhouse gas (GHG). The binder of concrete, Portland cement, is an intensive process in terms of energy and the use of raw materials and has significant emissions of GHG to the atmosphere. The need to achieve sustainability in the production of Portland cement involves improving current processes (implementation of new technologies and waste recovery as partial substitutes for fuels and raw materials) and developing new high-performance binders. This dissertation presents advances in understanding calcium aluminosilicate precursors and in evaluating their nature as precursors to produce alkali-activated binders (AABs). These binders are defined as the reaction products when an alkaline source is combined and reacts with aluminosilicates or calcium aluminosilicates precursors resulting in the development of mechanical strength. Characterizing cementitious materials demands advanced, non-traditional experimental techniques due to the complex and locally disordered nature of most chemical phases responsible for strength development and retention. This dissertation uses scanning transmission X-ray microscopy (STXM) as the main characterization method. Characterization of these materials by STXM revealed further insights about their composition at the nano- to micro-scale; specifically, the distribution and coordination of elements in hydrated or AABs. STXM is a technique that enables the nanometer-resolved spectromicroscopic investigation using brilliant synchrotron X-ray radiation as the incident beam. NEXAFS (X-ray absorption near edge structure) is the principia of STXM providing the coordination environment of several elements ( C, Ca, Al and Si were conducted in this dissertation). The first chapter is a State of the Art about alkali-activated materials precursors, amorphous materials, alumino-silicates properties, and the effect of calcium in the last ones. It includes some technical aspects about NEXAFS as the Principia of STXM, the microscope used for the dissertation. The dissertation (Chapters 2, 3, and 4) includes the characterization of synthetic precursors (raw materials aluminosiliceous or calcium aluminosiliceous promt to be activated), the intermediate products involved in alkali activation at 30 mins, and the final reaction products at 20h of curing (activator NaOH 8M at 85°C). Using the beamlines at the Advanced Light synchrotron facility in the Berkeley National Laboratory the precursors were studied using the NEXAFS edges Ca, C, Si, and Al. The use of high-resolution ptychography imaging allowed the characterization of the morphology. Additionally, samples that vary the calcium content have been studied, primarily using the aluminum and calcium edges. The results from the current research confirmed the literature results regarding the presence of fourfold aluminum with the additional presence of six-fold and probably five-fold coordinated Al. However, the present work shows that the at 27Al MAS NMR technique was inaccurate in studying Al coordination number in several stages of the precursors (Fro IETCC). Chapters 2-4 give experimental evidence of the six-fold coordinated Al in some precursors and activation products. Chapter 2 shows that, as a network modifier, calcium improves the precursors' reactivity, enhancing the structure's disorder. In addition, calcium exhibited properties of medium range ordering and, after a certain ratio, promotes the formation of crystalline phases that negatively affect the alkali-activation and reduce the mechanical strength of the AABs (when CaO content is superior to 20%). Furthermore, calcium behaves as divalent when CaO is added to the precursors, requiring two non-bridging oxygens to maintain charge balance. As a result, the oxygen environment surrounding the Ca atom differs significantly from that around the Na atoms, and this will affect the oxygen environment around the Si atoms. In the case of silicon, the inherent disordered nature of precursors gave a broad range of Si-O, Si-Si distances, and Si-O-Si angles. This disorder was demonstrated with the calculations of NBO/T and polymerization (Q). Chapter 3 reports with the high development of six-fold coordinated Al and the presence of CASH (calcium alumino-silicate hydrate) and CSH (calcium silicate hydrate phase) in calcium alkali-activated glasses. The phase noticed for 0% Ca is expected to be one-dimensional NASH (sodium silicate hydrate phase). Comparatively the aluminum white line has lower energy in calcium-free samples because calcium works as a charge compensator taking part in the amphoteric role of aluminum (acting as an amorphous-forming agent when Al ions occur in tetrahedral coordination and as modifying ions when they occur in octahedral coordination). With the use of Al K-edge, a particle with presence CASH was found. With the help of NEXAFS, it was evidenced that the denser region contains mostly four-fold coordinated Al with the presence of six-fold coordinated Al in the dendritic-like activated products in the mentioned particle. The external region of CASH characterized by some dendritic or fibrous morphology includes both Al coordination but with a significantly higher content of six-fold coordinated Al. For CASH the Ca L3/2-edge intensities ratios were like those identified by other authors with Al/Si=0.05 chemical composition. (calcium and sodium alumino-silicate hydrate) Chapter 4 reports that CASH and CNASH are the main products of the AABs. In the micrographs from STXM, the areas identified with a lower presence of calcium are characterized by CNASH. This last mineral phase has not been identified previously using STXM and its characteristic energy in calcium edge allowed the differentiation with CASH. In addition, some traces of unreacted precursors and calcite were identified in the AAB. Finally in the calcium-free sample and using Al-K edge, 3 dimensional NASH is characterized for the first time using STXM. In summary, the ultimate goal of the research in this dissertation is to extend the knowledge about alkali-activated binders starting from the characterization of amorphous materials (working as precursors of the reaction), passing the early stage of activation (30min), and, finally, to study the products of the final reactions at the late stage of activation (20h)