Showing papers by "Ángel Justo published in 1991"

Thermal and microstructural studies on mud with additives

Abstract: Mixtures of mud with various additives were studied to explain the reasons for the change in geotechnical properties. The additives were: lime, cement, fly ash, water-glass containing either Na2CO3 or CaCl2 and phosphogypsum. An increase in strength was usually associated with increase of weight loss, both on static or dynamic heating. An exothermic peak occurred between 420°C and 490°C., being especially high in the presence of water -glass, together with CaCl2. XRD indicated an increase in calcite content and the possible formation of calcium aluminate silicate hydrate. SEM showed a non-homogeneous microstructure and big pores in case of mixtures of low strength (water-glass addition). A homogeneous aggregated structure was obtained in the case of higher strength (fly ash, phosphogypsum).

A study of the thermal behaviour and geotechnical properties of a marine clay and its composites

Abstract: A change in geotechnical properties with the addition of fly ash was observed in a marine clay, which was intended for use in earth embankment reconstruction. This was correlated with the drying rate and weight loss on heating. Composites with the optimum fly ash content (6% to 8%) also indicated the highest drying rate ΔG/Δt for Δt=4 h to 1 d. Increase in composite strength was due to aggregation of the material and to the formation of a cementing compound from the amorphous matter present as shown by SEM. This resulted in an increase in weight loss, on heating, of the composite as compared to the parent material. Thus the study of the drying rate ΔG/Δt and weight loss on heating gives some information on microstructure and strength of the system, which were checked by XRD and SEM.

A simple diffractometer heating-cooling stage; application to the study of an organo-clay complex

Abstract: The study of the intercalation of organic compounds into clays, as in the preparat ion of pillared clays, is of great importance both from the theoretical point of view and for its applications in pharmacy, agriculture, clay characterization, catalysis, etc. (MacEwan and Wilson, 1980; Theng, 1974; Pinnavaia, 1983). At different temperatures, intercalated organic molecules, especially long-chain molecules, can undergo reversible phase transitions, and hydratable cations can hydrate to different degrees. These phenomena can be followed by studying the variat ion in X-ray powder diffraction (XRD) basal spacing with temperature (Brindley and Ray, 1964; Lagaly and Weiss, 1971; Pfirrmann et al., 1973). Although various temperature-control stages for powder X-ray diffractometers have been described in the literature (Brown et aL, 1972; Lagaly et aL, 1975; Morandi et al., 1976-1977), the advantage of the system described here is that XRD patterns can be obtained more simply and quickly for temperature ranges both below and above ambient room temperature and with greater temperature stability, due to the simultaneous use of cold and heat sources.