A comprehensive review of the models on the nanostructure of calcium silicate hydrates

The need to master factors affecting the performance of concrete has sparked research on its basic constituent, cement, whose properties are determined by one of the most critical cement hydration products, the calcium silicate hydrate. The present paper discusses the evolution of models describing the nanostructure of the calcium silicate hydrate (C–S–H) over the past century (descriptive models), with a focus on the models presented in the last fifteen years, 2000–2014 (descriptive and predictive models), marked with the breakthrough of nanotechnology. The purposes and outcomes of the suggested models are discussed, along with their limitations. The article concludes that notwithstanding the enormous potentials nanotechnology and advanced molecular modelling have offered in the field, modern models are, in essence, still expanding on the colloidal or layered models suggested in the 60s, rather than providing a ground breaking new approach. However, it is generally recognised that nanotechnology and molecular modelling have, facilitated the shift from descriptive to predictive models, saving time and resources by extrapolating results of very lengthy experiments, e.g. sorption isotherms, or by mathematically manipulating the C–S–H components to derive different structures and assemblages, that would have been difficult or impossible in practice. In that sense, the new experimental methods available, paired with analytical models are able to provide further justification of the pioneering studies and advance cement nanoscience, paving the way to the production of innovative, nanomodified cements, with minimum Portland cement content.