International audienceSome work has been carried out on the effect of calcium carbonate on cement paste, but there is no general agreement on the relative effects of different amounts of calcium carbonate on cement paste properties. The objective of the present work is to assess the effect of various amounts of calcium carbonate on the hydration of tricalcium silicate in order to explain the physico-chemical changes occurring during Portland cement hydration. It is shown that calcium carbonate has an accelerating effect on C3S and cement hydration and leads to the precipitation of some calcium carbosilicate hydrate

This work deals with the relative efficiency of polysaccharides and their influence on cement hydration. Several parameters such as the structure, concentration, average molecular weight, and soluble fraction value of polysaccharides were examined. Cement hydration was monitored by isothermal calorimetry, thermogravimetry (TGA), and infra-red spectroscopy (FTIR). Results clearly show that retardation increases with higher polysaccharide-to-cement weight ratio (P/C). Low molecular weight starch showed enhanced retarding effect on the hydration of cement. The retardation effect of polysaccharides is also dependant on the composition of cement.

a b s t r a c tThanks to their refractoriness, carbides are sensed as fuel coating for the IVth generation of reactors. Among those studied, the Ti 3 SiC 2 ternary compound can be distinguished for its noteworthy mechanical properties: the nanolamellar structure imparts to this material some softness as well as better toughness than other classical carbides such as SiC or TiC. However, under irradiation, its behaviour is still unknown. In order to understand this behaviour, specimens were irradiated with heavy ions of different energies, then characterised. The choice of energies used allowed separation of the effects of nuclear interactions from those of electronic ones.

International audienceCarbide-type ceramics, which have remarkable thermomechanical properties, are sensed to manufacture the fuel cladding of Generation IV reactors that should work at high temperature. The MAX phases, and more particularly titanium silicon carbide, are distinguished from other materials by their ability to have some plasticity, even at room temperature. For this study, polycrystalline Ti3SiC2 was irradiated with ions of different energies, which allow to discriminate the effect of both electronic and nuclear interactions. After characterization by low-incidence X-ray diffraction and cross-sectional transmission electron microscopy, it appears that Ti3SiC2 is not sensitive to electronic excitations while nuclear shocks damage its structure. The results show the creation of many defects and disorder in the structure, an expansion of the hexagonal close-packed lattice along the c axis, and an increase in the microstrain yield