1,720,990 research outputs found
Analysis of corrosion with electrochemical techniques applied to geothermal power plants in Switzerland
No full textCritical Analysis of Experiments on Reinforcing Bar Corrosion in Cracked Concrete
No full textCracks in concrete are expected to accelerate the degradation of
reinforced concrete—mainly reinforcement corrosion. Previous
literature studies have shown that the initiation time can decrease
due to cracks, whereas the accelerating effect on corrosion propagation
has no clear experimental evidence. This paper critically
assesses how different common experimental setups may influence
the test results. It is found that, particularly, the exposure duration
and condition, the water-binder ratio (w/b), and the crack width
have an impact on the outcome of the experimental study about
corrosion rates in cracked concrete. Hence, these parameters
should be carefully considered when designing experiments to
study the influence of cracks. Recommendations for future research
work are given
Chloride-induced corrosion of steel in concrete—insights from bimodal neutron and X-ray microtomography combined with ex-situ microscopy
Full text linkThe steel-concrete interface (SCI) is known to play a major role in corrosion of steel in concrete, but a fundamental understanding is still lacking. One reason is that concrete's opacity complicates the study of internal processes. Here, we report on the application of bimodal X-ray and neutron microtomography as in-situ imaging techniques to elucidate the mechanism of steel corrosion in concrete. The study demonstrates that the segmentation of the specimen components of relevance-steel, cementitious matrix, aggregates, voids, corrosion products-obtained through bimodal X-ray and neutron imaging is more reliable than that based on the results of each of the two techniques separately. Further, we suggest the combination of tomographic in-situ imaging with ex-situ SEM analysis of targeted sections, selected based on the segmented tomograms. These in-situ and ex-situ characterization techniques were applied to study localized corrosion in a very early stage under laboratory chloride-exposure conditions, using reinforced concrete cores retrieved from a concrete bridge. Several interesting observations were made. First, the acquired images revealed the formation of several corrosion sites close to each other. Second, the morphology of the corrosion pits was relatively shallow. Finally, only about half of the total 31 corrosion initiation spots were in close proximity to interfacial macroscopic air voids, and > 90% of the more than 160 interfacial macroscopic air voids were free from corrosion. The findings have implications for the mechanistic understanding of corrosion of steel in concrete and suggest that multimodal in-situ imaging is a valuable technique for further related studies
Modelling effect of coarse aggregates on oxygen transport and corrosion products precipitation in reinforced concrete
No full textThe structure of concrete, in particular the microstructure of the steel-concrete interface (SCI), can significantly affect corrosion of rebars. To support corrosion, oxygen needs to diffuse from the ambient environment to the steel surface. Meanwhile, corrosion products transport through the SCI and precipitate in concrete. Transport properties of concrete play an important role in these two processes. However, the effect of the heterogeneous structure of concrete especially coarse aggregates on oxygen transport and corrosion products precipitation in reinforced concrete is rarely studied in the literature. This study employed a numerical model to investigate such effect. Simulation domains in 2D were created with different aggregate contents and sizes. The model included oxygen diffusion, ions diffusion and migration, corrosion products oxidation and precipitation. The simulation results showed that the presence of aggregates significantly reduces oxygen diffusion. It becomes more pronounced for high aggregate contents which lead to more corrosion products formed at the interface. Furthermore, results showed that the interfacial transition zone (ITZ) around aggregates can enhance oxygen diffusion
Corrosion behaviour of L80 steel grade in geothermal power plants in Switzerland
Full text linkIn Switzerland, deep geothermal energy can give a promising contribution to the future
energy scenario. However, the expertise in operational issues of deep geothermal power plants is
limited, and technical challenges, such as corrosion, are a determining factor for their reliable and
long-term operation. In this work, two representative fluids of optimal geothermal conditions in
Switzerland were studied. The corrosiveness of the solutions was assessed using two experimental
setups that allow investigating the range of temperatures and pressures that apply to the reservoir
and power plant conditions. The corrosion behaviour of API L80 steel was analyzed by means of
electrochemical measurements (at 100 and 200 °C) and of gravimetric tests (at 100 °C). After the
tests, the morphologies and composition of the corrosion products were obtained by scanning
electron microscopy (SEM) coupled with energy dispersive X-Ray (EDX) and X-Ray diffraction (XRD).
Results show that corrosion rates are significantly high at 100 °C in environments with a chloride
concentration of around 600 mg/L and pH around 7. The corrosion products deposited on the metal
surface mainly consist of magnetite and/or hematite that might potentially form a protective layer.
This study gives a first insight of the potential corrosiveness of geothermal fluids in Switzerland
Laboratory tests simulating corrosion in geothermal power plants: influence of service conditions
Full text linkOne of the main challenges associated with the operation and maintenance of binary geothermal power plants is the degradation of construction materials. In this sense, it is crucial to apply appropriate preventive maintenance in critical components (such as the wellheads, heat exchangers, or pipes), while reducing shutdown times. Based on electrochemical measurements performed in an autoclave corrosion testing setup, we studied the corrosion mechanism of API L80 steel grade as a function of operational and/or maintenance procedures. We used a test fluid representative for a site in Switzerland, but the main observations made may be applicable in a wider context. We found that changes in the fluid temperature (from 200 to 100 °C) or temporary oxygen ingress significantly influenced the corrosion behavior of this carbon steel and increased its corrosion rate (from approx. 20 μm/year to > 120 μm/year). After a few days, the corrosion rate was found to decrease and stabilize around values of 50–70 μm/year, as a result of a porous corrosion product layer formed on the metal surface (approx. 250 μm thick). Electrochemical impedance spectroscopy indicated an increase in capacitance of the double layer over time, most likely due to an increase in the effective surface area of the steel sample, as a consequence of surface roughening due to corrosion. The results from this study may be implemented in the design and operation of future power plants in Switzerland and elsewhere to ensure reliable and cost-effective energy production from geothermal resources
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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