Application of various microscopy techniques to study early‐age and longer‐term behaviour of super sulphated cement microstructure.

Super sulphated cement (SSC) is a very promising substitute for traditional construction materials (i.e. Portland cement), due to its enhanced durability and particularly low environmental impact. This paper explores the microstructure and certain properties of SSC, focusing on the particular complexities of its microstructure and the difficulties of microanalysis of its hydrates. To do so, SSC paste samples were first cast to identify hydration products using X‐ray diffraction, then observed at early age using confocal laser scanning microscopy (CLSM) and at early and late age using scanning electron microscopy. In addition, concrete cores impregnated with fluorescein in order to highlight porosity, cracking and aggregates debonding were observed under UV light using optical microscopy (OM), showing a complete absence of cracking and aggregate debonding. Both microscopy techniques (CLSM and UV light OM) have been applied to this type of binder for the first time. The results show that SSC microstructure is characterised by a sophisticated intergrowth of various phases, including ettringite and amorphous calcium‐(alumina)‐silicate hydrate gels. Finally, Monte–Carlo simulation of electron‐matter has been provided for a better understanding of EDS analysis. LAY DESCRIPTION: This work focuses on the study of a particular construction material known as super sulphated cement (SSC). SSC appears to be a promising alternative to traditional building materials as it offers improved durability reduced and environmental impact attributed to its composition comprising at least 75% of a by‐product of the steel industry. This study investigates the microstructure and properties of this type of cement, focusing particularly on its complex microstructure and the challenges posed by the analysis of its hydration products. To do this, samples of SSC cement paste were first cast to identify hydration products using X‐ray diffraction. They were then examined at early stages using confocal laser scanning microscopy (CLSM) and at early and late stages using scanning electron microscopy (SEM). In addition, fluorescein‐impregnated SSC concrete cores were observed under ultraviolet (UV) light using optical microscopy (OM) to highlight porosity, cracking and delamination of aggregates, phenomena that may be present in such materials. These observations revealed the absence of these problems on this type of cement in this work. This research marks the first application of CLSM and OM under UV light to this type of cement. These microscopic techniques enabled us to understand the hydration phenomenon of this type of cement and its highly complex morphology. Finally, Monte–Carlo simulation was used in this study to model electron‐matter interaction, enabling us to understand the elemental analyses obtained and to gain a better understanding of the microstructure of SSC samples. [ABSTRACT FROM AUTHOR]