This work aims at studying the electrochemical behavior, by Electrochemical Impedance Spectroscopy (EIS), of austenitic (AISI 304 and AISI 316) and duplex (SAF 2205 and SAF 2304) stainless steels, ...when embedded in concrete specimens. Concrete specimens were exposed to chloride containing solutions simulating the aggressive conditions found in sweater environments. Samples were fully immersed and submitted to periodic immersion/emersion cycles. EIS and open circuit potential (OCP) were monitored in a monthly basis. Samples containing carbon steel (C-steel) rebars were also prepared for comparison of the corrosion rates between the different materials.
The results showed that the austenitic and duplex SAF 2205 stainless steels were passive for all the testing period, due to the formation of protective oxide layer, with the AISI 316 presenting the higher corrosion resistance value. The EIS results suggest an increase of more than one order of magnitude in the corrosion resistance of the duplex steels and AISI 316 comparatively to C-steel rebars.
BV equivalence with boundary Simão, F. M. Castela; Cattaneo, A. S.; Schiavina, M.
Letters in mathematical physics,
2023/2, Letnik:
113, Številka:
1
Journal Article
Recenzirano
Odprti dostop
An extension of the notion of classical equivalence of equivalence in the Batalin–Vilkovisky (BV) and Batalin–Fradkin–Vilkovisky (BFV) frameworks for local Lagrangian field theory on manifolds ...possibly with boundary is discussed. Equivalence is phrased in both a strict and a lax sense, distinguished by the compatibility between the BV data for a field theory and its boundary BFV data, necessary for quantisation. In this context, the first- and second-order formulations of nonabelian Yang–Mills and of classical mechanics on curved backgrounds, all of which admit a strict BV–BFV description, are shown to be pairwise equivalent as strict BV–BFV theories. This in particular implies that their BV complexes are quasi-isomorphic. Furthermore, Jacobi theory and one-dimensional gravity coupled with scalar matter are compared as classically equivalent reparametrisation-invariant versions of classical mechanics, but such that only the latter admits a strict BV–BFV formulation. They are shown to be equivalent as lax BV–BFV theories and to have isomorphic BV cohomologies. This shows that strict BV–BFV equivalence is a strictly finer notion of equivalence of theories.
Concrete properties can be improved by various additives. Nowadays there is a strong interest concerning the use of spent fluid catalytic cracking catalyst (SFCC) as an admixture to improve ...mechanical properties of concrete. This work aims at studying the corrosion resistance of steel rebars in SFCC modified mortar specimens. Results of physicochemical characterization indicate the acceleration of cement hydration due to pozzolanic activity of SFCC. Electrochemical measurements show that the addition of the SFCC enhances corrosion resistance by delaying its corrosion onset and decreasing the corrosion rate. These benefits can be attributed to the reduction of the mortar permeability.
Corrosion of reinforcing steel in concrete is a worldwide problem. An important factor affecting such process is the concrete composition and, especially the presence of additives. In fact, the ...kinetics of water absorption and water evaporation are affected both by the environment conditions and by the nature of the additives. This is important for powdered additives, which can partially occlude the porous structure, changing porosity and permeability of concrete too.
Reinforced concrete samples were modified by adding spent fluid cracking catalyst powders (SFCC) and an environment friendly commercial inhibitor. The samples were submitted to consecutive cycles of 15day of immersion (in saturated NaCl electrolyte) followed by 15day of drying. Samples were regularly monitored by electrochemical Impedance Spectroscopy (EIS). The results revealed that the additives interfere with the water adsorption/evaporation kinetics in concrete, a process resulting from the joint effect of diffusion and capillary processes. These interferences occur due to three combined mechanisms: two related to pore blocking and pozzolanic activity, which are the result of structural changes in concrete and affect the diffusion processes/mechanism; the third one is the capillary mechanism, which is strongly dependent from the chemical nature of the additives, but can also be influenced by structure modifications. This mechanism can increase, reduce or eliminate the capillary processes.
This work aims at studying the response of unsupported concrete media by Electrochemical Impedance Spectroscopy (EIS) and its influence in the results obtained for steel corrosion in reinforced ...concrete samples. Measurements carried out in full immersed samples correspond to a typical electrolyte media, presenting essentially a resistive behavior. Thus, rebar corrosion, which appears commonly at intermediate frequency region, can be assessed and easily interpreted.
For samples in partial dry conditions the spectra show several time-constants distributed across the entire frequency range. In the high frequency region, the time constant is ascribed to dielectric properties of the system. At low frequencies the time constant corresponds to the ionic depletion, while the time constant at intermediate frequencies result from charge separation inside the material bulk, typically of unsupported media. Interpretation of the results obtained by EIS for concrete reinforced steel in partial dry conditions cannot be fully interpreted without considering the dielectric behavior of the system.
A capacitance model for the estimation of water uptake in polymeric coatings is presented. The model is based upon a linear combination of the individual capacitances of the polymeric phase, the ...water and the air contained in the coating. Experimental comparison of the model with gravimetric data has revealed an improvement with respect to the classical equations.
Efforts have been made to create new procedures based on Electrochemical Impedance Spectroscopy (EIS) to study several characteristics of cementitious materials with practical interest. Similar ...approaches can be followed to study other materials, in which the comprehension of their physical, transport-related and durability properties are also needful. Natural stones are one of these materials, wherein such properties play a fundamental role on their performance when in service, in both monumental and non-monumental constructions.
This work aims at presenting a first approach on the application of EIS to study electrolyte absorption and evaporation processes in stones. Stones with different porosities and different fluid-transport behaviors were monitored by EIS using a setup of 4 or 2 electrodes assemblies.
During absorption, EIS spectra presented two distinct responses according to the frequency, a resistive behaviour and a capacitive slope. The evolution of the spectra showed that the absorption process can be accurately monitored in less porous stones, whereas in more porous stones the procedure still requires some improvements.
In what concerns evaporation tests, EIS spectra were more complex, especially for longer periods. At early stages two time constants were poorly detectable, but the evolution of evaporation produced progressive modifications on the spectra and a second time constant became well-resolved, as result of two effects: a gradual loss of contact efficiency and a decrease of moisture within the pores.
In both cases EIS enabled to distinguish between different fluid-transport behaviors and showed to be dependent upon the moisture content within the pores and open porosity of each stone variety.
Biomonitoring programs to access the ecological integrity of freshwaters tend to rely exclusively on structural parameters. Here we evaluated stream ecological integrity using (a) benthic ...macroinvertebrate derived metrics and a biotic index as measures of structural integrity and (b) oak litter decomposition and associated fungal sporulation rates as measures of functional integrity. The study was done at four sites (S1, S2, S3 and S4) along a downstream increasing phosphorus and habitat degradation gradient in a small stream. The biotic index, invertebrate metrics, invertebrate and fungal communities' structure and sporulation rates discriminated upstream and downstream sites. Decomposition rates classified sites S4 and S2 as having a compromised ecosystem functioning. Although both functional and structural approaches gave the same results for the most impacted site (S4), they were complementary for moderately impacted sites (S2 and S3), and we therefore support the need for incorporating functional measures in evaluations of stream ecological integrity.
This study supports the need for incorporating functional measures in evaluations of stream ecological integrity.
Small forest streams and their riparian vegetation are closely linked ecosystems. Stream consumers obtain most of their energy from leaf litter provided by the terrestrial vegetation. Thus, ...understanding the relationship between riparian vegetation, aquatic communities and litter decomposition may help explaining the variability in aquatic communities and processes among non-impacted streams, and anticipate their responses to anthropogenic-induced changes in the riparian vegetation. We surveyed 10 small non-impacted forest streams in central Portugal for riparian vegetation (species richness), benthic litter (species richness and biomass), aquatic hyphomycete conidia in transport (species richness and conidia concentration) and macroinvertebrates associated with benthic litter (taxon richness, density and biomass), during the litter fall peak. We found significant correlations between (a) aquatic communities and riparian vegetation species richness, (b) aquatic communities and benthic litter species richness and biomass and (c) within aquatic communities. Oak litter decomposition rates (from a previous experiment on the same streams) were also correlated with riparian tree species richness. This survey showed that spatial variability in riparian vegetation, benthic litter, aquatic communities and litter decomposition can be high even within a relatively small area, and allowed the identification of complex interactions between these components of the aquatic detrital food web. The positive correlation between aquatic hyphomycete species richness, macroinvertebrate taxon richness, litter decomposition and riparian tree species richness suggests that anthropogenic-induced decreases in riparian species richness may affect aquatic communities and processes. Surveys over streams naturally differing in environmental conditions may allow forecasting the response of aquatic communities and processes to anthropogenic activities.
Aim: We tested the hypothesis that shredder detritivores, a key trophic guild in stream ecosystems, are more diverse at higher latitudes, which has important ecological implications in the face of ...potential biodiversity losses that are expected as a result of climate change. We also explored the dependence of local shredder diversity on the regional species pool across latitudes, and examined the influence of environmental factors on shredder diversity. Location: World-wide (156 sites from 17 regions located in all inhabited continents at latitudes ranging from 67° N to 41° S). Methods: We used linear regression to examine the latitudinal variation in shredder diversity at different spatial scales: alpha (a), gamma (y) and beta (P) diversity. We also explored the effect of y-diversity on a-diversity across latitudes with regression analysis, and the possible influence of local environmental factors on shredder diversity with simple correlations. Results: Alpha diversity increased with latitude, while y-and p-diversity showed no clear latitudinal pattern. Temperate sites showed a linear relationship between y-and a-diversity; in contrast, tropical sites showed evidence of local species saturation, which may explain why the latitudinal gradient in a-diversity is not accompanied by a gradient in y-diversity. Alpha diversity was related to several local habitat characteristics, but y-and ß-diversity were not related to any of the environmental factors measured. Main conclusions: Our results indicate that global patterns of shredder diversity are complex and depend on spatial scale. However, we can draw several conclusions that have important ecological implications. Alpha diversity is limited at tropical sites by local factors, implying a higher risk of loss of key species or the whole shredder guild (the latter implying the loss of trophic diversity). Even if regional species pools are not particularly species poor in the tropics, colonization from adjacent sites may be limited. Moreover, many shredder species belong to cool-adapted taxa that may be close to their thermal maxima in the tropics, which makes them more vulnerable to climate warming. Our results suggest that tropical streams require specific scientific attention and conservation efforts to prevent loss of shredder biodiversity and serious alteration of ecosystem processes.
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