Identification des phases sous-hydratées du sulfate de calcium

L'utilisation de moyens et de procédures expérimentales adaptées a permis d’identifier chimiquement et structuralement deux formes sous-hydratées de sulfate de calcium : CaSO4, 0,5 H2O et CaSO4, 0,6 H2O.Avec l’hanhydrite soluble - γ-CaSO4 - à laquelle elles s'apparentent structuralement ce sont les trois phases distinctes entrant dans la constitution du plâtre

Weed interference with peppermint (Mentha x piperita L.) and spearmint (Mentha spicata L.) crops under different herbicide treatments: effects on biomass and essential oil yield

BACKGROUND: ‘Minor crops’ such as spearmint and peppermint are high added value crops, despite the fact that their production area is comparably small worldwide. The main limiting factor in mint commercial cultivation is weed competition. Thus, field experiments were carried out to evaluate the effects of weed interference on growth, biomass and essential oil yield in peppermint and spearmint under different herbicide treatments. RESULTS: The application of pendimethalin and oxyfluorfen provided better control of annual weeds resulting in higher crop yield. Additionally, when treated with herbicides both crops were more competitive against annual weeds in the second year than in the first year. All pre-emergence herbicides increased biomass yield, since pendimethalin, linuron and oxyfluorfen reduced the density of annual weeds by 71–92%, 63–74% and 86–95%, respectively. Weed interference and herbicide application had no effect on essential oil content; however, a relatively strong impact on essential oil production per cultivated area unit was observed, mainly due to the adverse effect of weed interference on plant growth. CONCLUSION: Considering that pendimethalin and oxyfluorfen were effective against annual weeds in both spearmint and peppermint crops, these herbicides should be included in integrated weed management systems for better weed management in mint crops. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industr

Thermo-poro-mechanics Modelling of Gypsum Dehydration

Understanding the behaviour of natural calcium sulphates is important to ensure the sustainable integrity of civil structures. The phase transitions of these minerals are associated with considerable volume variations, creation of porosity with local defects, and water exchanges. Such changes can jeopardise the integrity of structures when the conditions that trigger the phase transitions are encountered. This paper uses advanced poromechanics to investigate the dehydration of gypsum when subjected to heating. The proposed approach includes the fundamental principles of non-equilibrium thermodynamics as well as the coupled multi-physics of thermal, hydraulic, mechanical and chemical (THMC) processes. A novel mathematical formulation is introduced to describe the coupled constitutive relationships in the reversible and dissipative regimes as well as the consequent partial differential equations that describe the THMC processes. The governing equations are integrated numerically using the finite element method. The obtained results show a significant correlation between gypsum dehydration and creation of fluid pathways. The proposed model can be generalised to describe the effects of dehydration in other minerals carrying water in their crystal structures.</p