Myriam Duc

Role of interfacial chemistry on the rheology and thermo-mechanical properties of clay-polymer nanocomposites for building applications

This study is directed towards investigating the role of the surface treatment of clay particles on the rheological and thermomechanical behaviour of clay-epoxy blends. Nanocomposites were prepared by mixing small amounts (5–10 mass %) of commercial organoclays or raw clays with an epoxy system commonly used in civil engineering. Rheological characterisations in the liquid state revealed a pronounced thixotropic character of the organoclay-based systems, which all exhibited a shear-thinning behaviour above a critical stress threshold (yield stress), depending on both the intensity of interfacial interactions and the degree of filler dispersion. On the other hand, systems based on raw clay particles behaved like Newtonian fluids, in the same way as the unreinforced polymer matrix. Complementary dynamic mechanical analyses (DMA) performed on the cured cross-linked nanocomposites also showed significant changes in the viscoelastic behaviour of the epoxy matrix due to the introduction of organoclays, whereas only minor variations were observed following the introduction of raw fillers. These results were consistent with nanoscale morphological characterisations performed by conventional X-ray diffraction (XRD) on the various hybrid systems. In this context, rheology and DMA appear as attractive alternative methods for assessing the filler dispersion at a macroscopic (and possibly more relevant) scale. This research is of practical interest for civil engineers, since clay reinforced-epoxies could in the future be used as coating materials with enhanced barrier performances, in order to protect infrastructures against environmental ageing or corrosion.

Effect of different drying methods on the mechanical behavior and the microstructure of an Algerian compacted limestone crust

Abstract This experimental work aims to better understand the hardening process of limestone tuff after compaction when water content varies. Indeed, the pavements built with wet calcareous crust or tuff are hardened by the effect of compaction followed by water evaporation but this cohesion after compaction disappears completely by total saturation. In order to classify the materials according to geotechnical specifications related to limestone crusts, tuff from Faidh el Botma area was studied by following the change of compressive strength measured on specimens prepared at different water contents and stored for several days either under air (for fast drying) or in non-hermetic bags (for slow drying). The first series of specimens appeared more resistant than the second one. As explanation of the hardening, the possible precipitation of new phases such as carbonate during the fast drying is discussed based on chemical and microstructural observations as well as the effect of suction than could change the microstructural arrangement of tuff particles when the moisture content varies.