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Due to its complexity at nanoscale, calcium silicate hydrate (C-S-H), the dominant binding phase in cement hydrates, is not yet completely understood. In this study, molecular dynamics was employed to simulate the hydration products at low and high calcium/silicon ratios. It was found that two morphologies of calcium silicate hydrate gels can be distinguished - a branched structure at low calcium/silicon ratios and an ellipsoid particle structure at high calcium/silicon ratios. Using virtual X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and small-angle neutron scattering (SANS) techniques, the simulated structures were characterised, confirming that they show features of calcium silicate hydrate as revealed by experimental approaches. The short-range structures of calcium and silicon atoms and the distorted calcium tetrahedrons resemble the features of silicate glasses obtained from experiments, implying the amorphous nature of the local structure in calcium silicate hydrate gel. Furthermore, formation mechanisms for the two morphologies are proposed. In the hydration process, calcium ions play roles in depolymerising the silicate structure and preventing the amorphous network formation. Therefore, at low calcium/silicon ratios, the reaction is governed by silicate skeleton growth, but at high calcium/silicon ratio, aggregations of calcium ions and short silicate chains dominate. [ABSTRACT FROM AUTHOR]

In masonry, the most commonly used materials are concrete blocks or burnt clay brick. Owing to energy costs, there is a need to explore alternative raw materials and energy-efficient technologies for making building materials. This paper deals with the incorporation of blast furnace granulated slag in sand-lime materials as a replacement for hydrated lime during autoclaving conditions. The slag grain-size grinding and the heat treatment in saturated vapour pressure autoclave conditions were investigated to study the compressive strength behaviour of the new material. This substitution induces a decrease in compressive strength. The reaction products consist mainly of 11 nm tobermorite and xonotlite. The X-ray diffractions of these phases are difficult to see. The slag seems more reactive with lime than quartz. Observations with the scanning electron microscope allow better appreciation of these crystallites. With its composition and amorphous structure, the granulated slag does not release new distinct phases of hydrates. [ABSTRACT FROM AUTHOR]