A highly osmotolerant rhizobial strain confers a better tolerance of nitrogen fixation and enhances protective activities to nodules of Phaseolus vulgaris under drought stress

The effect of water deficiency on nodules of common bean (Phaseolus vulgaris) inoculated with three rhizobial strains differing in their osmotolerance, was investigated in two different experiments on sterile sand. In the first experiment, the control plants were maintained at 90% field capacity (FC) and water-deficient plants were grown at 35% FC. The nitrogen fixation and growth parameters drastically decreased under water deficiency, however the three rhizobial strains, Rhizobium etli A32 (sensitive), Rhizobium tropici CIAT899 (tolerant), and Ensifer meliloti 4H41 (highly tolerant), showed different symbiotic performances. E. meliloti 4H41 allowed the best acetylene reduction activity (ARA) and biomass production and the highest number of large-sized nodules, while no significant effect was observed on lipid peroxidation, protein and legheamoglobin contents. The effect on antioxidant activities was the lowest. In the second experiment, plants were maintained at 90% FC during 45 days and then watering was stopped. The results showed that, the response to water deficit was quite similar for the three analyzed symbioses until 35% FC, but below this value of FC, symbiosis involving strain E. meliloti 4H41 was the most tolerant. This tolerance was accompanied, by in both experiments, by a stability of metabolic indices and protective antioxidant activities. These results suggest that, the relative tolerance of the nodules induced by strain 4H41 could be due to a constructive adaptation involving specific cortex structure and stress-adapted metabolic activities acquired during nodule formation and growth, rather than to a timely inducible response due to the stimulation of antioxidant enzymes. This suggestion should be confirmed through microscopic structure analysis and supplemental key enzymes in nodule metabolism such as sucrose synthase and malate dehydrogenase.Key words: Antioxidant activities, in pots experiment, leghemoglobin content, nodule, rhizobia, osmotolerance, symbiotic efficiency, water deficiency

Behavior of limestone filler cement mortars exposed to magnesium sulfate attack

WOS:000342367500042International audienceIn the cement production industry, looking for a less expensive binder using industrial waste and natural resources has become a major concern for the deficit level in the manufacture of Portland cement. However, despite the technical, economic and environmental benefits brought by the use of blended cements, they are associated with disadvantages. The objective of this paper is to study the effects of the incorporation of limestone fillers on the mechanical properties and durability of mortars prepared in different combinations based on this admixture material. The durability was evaluated after immersing the specimens in a 5% solution of magnesium sulfate for periods up to 360 days, and the penetration of chloride ions. The test results demonstrated that mortar and paste samples incorporating higher replacement levels of limestone filler were more susceptible to sulfate attack. According to microstructural analysis, such as DRX, the deterioration was significantly associated with formation of thaumasite, gypsum, and the brucite in the deteriorated parts of the specimens

Behavior of limestone filler cement mortars exposed to magnesium sulfate attack

WOS:000342367500042International audienceIn the cement production industry, looking for a less expensive binder using industrial waste and natural resources has become a major concern for the deficit level in the manufacture of Portland cement. However, despite the technical, economic and environmental benefits brought by the use of blended cements, they are associated with disadvantages. The objective of this paper is to study the effects of the incorporation of limestone fillers on the mechanical properties and durability of mortars prepared in different combinations based on this admixture material. The durability was evaluated after immersing the specimens in a 5% solution of magnesium sulfate for periods up to 360 days, and the penetration of chloride ions. The test results demonstrated that mortar and paste samples incorporating higher replacement levels of limestone filler were more susceptible to sulfate attack. According to microstructural analysis, such as DRX, the deterioration was significantly associated with formation of thaumasite, gypsum, and the brucite in the deteriorated parts of the specimens

Behavior of limestone filler cement mortars exposed to magnesium sulfate attack

In the cement production industry, looking for a less expensive binder using industrial waste and natural resources has become a major concern for the deficit level in the manufacture of Portland cement. However, despite the technical, economic and environmental benefits brought by the use of blended cements, they are associated with disadvantages. The objective of this paper is to study the effects of the incorporation of limestone fillers on the mechanical properties and durability of mortars prepared in different combinations based on this admixture material. The durability was evaluated after immersing the specimens in a 5% solution of magnesium sulfate for periods up to 360 days, and the penetration of chloride ions. The test results demonstrated that mortar and paste samples incorporating higher replacement levels of limestone filler were more susceptible to sulfate attack. According to microstructural analysis, such as DRX, the deterioration was significantly associated with formation of thaumasite, gypsum, and the brucite in the deteriorated parts of the specimens

Stratigraphy of the Hameima and lower Fahdene Formations in the Tadjerouine area (Northern Tunisia)

In the Tadjerouine area of north-western central Tunisia, the Albian transgression is characterized by deposition of alternating marls, limestones and sandstones (Hameima Fm) that overly massive platform carbonate rocks (Serdj Fm). The continuing transgression results in deposition of a thick series of marls and shales with subordinate carbonate beds (Fahdene Fm). A detailed study of the Hameima Fm, previously ascribed to the Late Aptian, shows that this formation can be subdivided into three members, all of earliest Albian age (Leymeriella tardefurcata Zone). The top of the Hameima Fm is slightly diachronous in the study area. A similar study of the Lower Shales of the Fahdene Fm demonstrates that they belong to the L. tardefurcata Zone and to the lower part of the Douvilleiceras mammillatum superzone. The overlying Allam limestones, formerly considered Middle Albian in age, are mainly of late Early Albian age (upper part of the D. mammillatum Superzone and Lyelliceras pseudolyelli Zone), although an extension into the lower Middle Albian cannot be ruled out. The Allam limestones are abruptly overlain by a diachronous series of Late Albian shales (Middle Shales of the Fahdene Fm), thus evidencing a stratigraphic hiatus of most of the Middle Albian and part of the early Late Albian. Our new data will lead to revision of the range of some Aptian/Albian orbitolinids and Albian planktic foraminifera

Mechanical, Microstructure, and Corrosion Characterization of Dissimilar Austenitic 316L and Duplex 2205 Stainless-Steel ATIG Welded Joints

The present work analyzed the microstructure, mechanical, and corrosion properties of a dissimilar activated tungsten inert gas (ATIG) welded 2205 duplex stainless-steel (2205 DSS) plate and AISI 316L austenitic stainless steel (316L ASS) and compared them to conventional dissimilar welded tungsten inert gas (TIG). The mixing design method is a tool used to establish the optimal combined flux to achieve a full-penetrated weld bead in one single pass. A microstructure study was carried out by scanning electron microscopy (SEM). The ATIG and TIG fusion zones revealed a matrix ferrite structure with intragranular austenite, Widmanstätten needles, allotriomorphic austenite at the grain boundaries, and plate-like precipitates free of deleterious phases such as sigma and chi phases or second austinite owing to the moderate heat input provided of 0.8 kJ/mm. Ferrite volume proportion measurements were carried out utilizing the areas image processing software. The average ferrite volume proportion attained 54% in the ATIG weld zone; however, it decreased to 47% for the TIG weld zone. The results showed that the optimal flux composed by 91% Mn2O3 and 9% Cr2O3 allowed a full penetrated weld to be obtained in one single pass. However, a double side weld is required for conventional TIG processes. The values of the tensile (599 Mpa), hardness (235 HV), and impact test (267 J/cm2) measurements of ATIG welds were close to those of conventional TIG welds. The elaborated flux did not degrade the mechanical properties of the joint; on the contrary, it reinforced the strength property. The width of the ATIG heat-affected zone was narrower than that of TIG welding by 2.6 times, ensuring fewer joint distortions. The potentiodynamic polarization test results showed a better electrochemical behavior for ASS 316L than with the weldment and the parent metal of DSS 2205

Effects of ATIG Welding on Weld Shape, Mechanical Properties, and Corrosion Resistance of 430 Ferritic Stainless Steel Alloy

Flux activated tungsten inert gas (ATIG) welding is a variant of tungsten inert gas (TIG) welding process with high production efficiency, high quality, low energy consumption, and low cost. The study of activating flux mechanism by increasing weld penetration has direct significance in developing flux and welding process. This study has been conducted on 430 ferritic stainless steel alloy. Design of experiment is used to get the best formulation of flux. Based on Minitab17 software, nineteen compositions of flux were prepared using the mixing method. Fluxes are combinations of three oxides (MoO3-TiO2-SiO2). Using the optimizer module available in Minitab 17 software, the best formulation was obtained to achieve the best weld depth. Hence, the obtained depth is twice greater than that achieved by conventional TIG welding. Moreover, mechanical properties and corrosion resistance have been investigated for TIG and ATIG welds respectively in tensile, impact, and hardness tests, and in potentiodynamic polarization measurement test