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Nanoscale ordering in conventional and alternative cementitious materials

Understanding the formation mechanisms and phase stability of amorphous aluminosilicates is extremely important for a range of geological and industrial processes including zeolites, glasses and low-CO2 alkali-activated cements. However, due to their disordered nature at the atomic length scale it is difficult to elucidate the exact structural rearrangements occurring during formation. Until now the atomic/nanoscale ordering present in alkali-activated cements has been described using existing knowledge of ordinary Portland cement (OPC)-based cement, specifically the nanocrystalline nature of the calcium-silicate-hydrate gel. Experimental pair distribution function analysis is a powerful tool capable of elucidating the local structural motifs present in amorphous/nanocrystalline materials. This technique is well-suited for studying the structural arrangements in disordered aluminosilicates, including glasses and cements. Here, by utilizing pair distribution function analysis it will be shown that the atomic structure of calcium-aluminum-silicate-hydrate gel (found in alkali-activated slag cements) is intrinsically different to calcium-silicate-hydrate gel known to exist in OPC-based concrete. This fundamental difference (amorphous versus nanocrystalline) draws into question the suitability of OPC-based approaches (thermodynamic modeling, atomic ordering, phase formation) for studying alkali-activated cement systems.

Author(s):

Claire White    
Princeton University
United States