Service life and durability of reinforced concrete structures have become crucial issues in all industrialized countries because of their economic and ecological relevance. Limited durability is ...frequently due to deterioration of steel and cement-based materials, such as mortar and concrete, by interactions with water and aggressive aqueous solutions. Neutron imaging has proved to be a powerful non-destructive technique to study quantitatively water content and water movement in porous materials. A neutron beam is much more attenuated by hydrogen in water than by most other elements present in cement-based materials.
In this review, focus is placed on applications of both two-dimensional neutron radiography and three-dimensional neutron tomography to investigate specific aspects of durability and deterioration of cement-based materials. Examples of results obtained by qualitative and quantitative investigations of moisture movement in cracked and uncracked cement-based materials are presented. Self-healing, efficiency of water repellent treatment, internal curing, frost damage, fire spalling, ettringite formation and observations of various reinforced concrete components are addressed. The results obtained by neutron imaging provide a solid basis for better understanding of deterioration mechanisms of cement-based materials. Recent improvements of neutron imaging facilities have allowed unexpected possibilities to study complex processes in cement-based materials. The potential for further research based on this promising technology is outlined and discussed.
Measured from a bag of sand taken in large rivers, the concentration of cosmogenic nuclides such as in situ-produced 10Be, 26Al, and 14C can be used to constrain the mean sediment flux of the ...headwaters and assess the duration of sediment storage from source to sink. We revisit these principles, with examples from the Amazon and Ganga basins.
We identify two end member cases controlling the concentration of cosmogenic nuclides in lowland river sediment: 1) if the time scale of floodplain sediment storage is short compared to the half-life of the nuclide, in situ cosmogenic nuclide concentrations are not significantly altered in lowland basins. In this case the concentration of e.g. in situ-produced 10Be in the sediment taken in the lowland basin equals in most cases that exported from the sediment source area, but the variability in nuclide concentrations between headwater streams is significantly averaged-out. Thus to convert the measured river sediments' in situ cosmogenic nuclide concentration into a catchment-wide denudation rate, production rates are scaled to include those of the sediment-producing mountainous areas only, rather than the entire catchment area. Nuclide production in the lowlands, where no sediment is being produced, is hence excluded. This correction is termed “floodplain correction”. 2) If sediment buried for periods of the order of the nuclides´ half-life is episodically re-entrained into the active river, paired nuclides, for example the ratio of 26Al/10Be, through the differential decay of these isotopes, constrain the the storage duration and re-mixing of floodplain sediment.
As in-situ cosmogenic nuclides measure denudation rates over longer time scales, typically integrating between 103 and 105years, their combination with modern estimates of sediment fluxes from river load gauging offers a rich potential of deciphering the controls of Earth surface fluxes across large basins. From this combination, we can assess how river systems react to external perturbations such as climate change or human interference, and how such signals are transmitted through the alluvial reaches of lowland basins. The most important results in both basins are that i) lowland Amazon and Ganga nuclide concentrations indeed broadly reflect the spatial average of Andean and Himalayan denudation, respectively, ii) the thus calculated sediment fluxes are within uncertainty of modern fluxes from sediment gauging, indicating complete sediment delivery to the sea without net loss into the basin, and iii) only the Amazon basin, given its size, contains a substantial fraction of sediment buried temporarily in the Quaternary.
Finally, we provide a short introduction to the use of meteoric cosmogenic nuclide 10Be and its ratio to stable 9Be, released by rock weathering, in lowlands. In the Amazon basin we show that 10Be concentrations in fine-grained suspended loads, depth-integrated over the water column using Al/Si ratios, provide erosion rates whereas the 10Be/9Be ratio on Be adsorbed to particles provides the denudation rate. Both are similar to denudation rates from in situ10Be. We show that this system responds more sensitively to sediment storage than the in situ system, and both accumulation and decay of meteoric concentrations may thus be used to determine sediment residence time.
•Source-to-sink sediment fluxes from long-lived cosmogenic nuclides (in situ10Be)•Controls of Earth surface fluxes across river basins over kyr-long temporal scales•Ganga and Amazon nuclide concentrations reflect their mean headwater erosion signals.•In situ- and meteoric-derived erosion in Amazon basin in good agreement
Acylcarnitine metabolites have gained attention as biomarkers of nutrient stress, but their physiological relevance and metabolic purpose remain poorly understood. Short-chain carnitine conjugates, ...including acetylcarnitine, derive from their corresponding acyl-CoA precursors via the action of carnitine acetyltransferase (CrAT), a bidirectional mitochondrial matrix enzyme. We show here that contractile activity reverses acetylcarnitine flux in muscle, from net production and efflux at rest to net uptake and consumption during exercise. Disruption of this switch in mice with muscle-specific CrAT deficiency resulted in acetyl-CoA deficit, perturbed energy charge, and diminished exercise tolerance, whereas acetylcarnitine supplementation produced opposite outcomes in a CrAT-dependent manner. Likewise, in exercise-trained compared to untrained humans, post-exercise phosphocreatine recovery rates were positively associated with CrAT activity and coincided with dramatic shifts in muscle acetylcarnitine dynamics. These findings show acetylcarnitine serves as a critical acetyl buffer for working muscles and provide insight into potential therapeutic strategies for combatting exercise intolerance.
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•CrAT is a mitochondrial enzyme that interconverts acetyl-CoA and acetylcarnitine•Acetylcarnitine in blood and tissues has emerged as a biomarker of energy surplus•Muscle contraction stimulates acetylcarnitine uptake, recycling, and oxidation•CrAT-mediated acetyl group buffering is essential for optimal exercise performance
Seiler et al. investigate exercise fatigue due to metabolic inertia and show that the nutritionally regulated enzyme carnitine acetyltransferase (CrAT), which interconverts acetyl-CoA and acetylcarnitine, plays a key role in modulating muscle energy economy. CrAT modulation could prove a useful strategy in delaying muscle fatigue and combatting exercise intolerance.
Two of the main activities of RILEM Technical Committee 208-HFC Subcommittee 2 were the preparation and publication of the state-of-the-art report on durability of strain hardening cement-based ...composites (SHCC), and the performance of comparative laboratory testing on SHCC. In this paper the comparative mechanical tests are reported, as performed in laboratories of five participating institutions. The purpose was to investigate and compare the crack patterns in terms of crack widths and spacing, and subsequently to make recommendations for a suitable test setup and procedure towards characterizing cracking in this class of materials. Such standardized procedures are required for future systematic and objective research towards durability of these materials in their in-service conditions, i.e. their resistance to deterioration processes in the cracked state. Standardized test procedures are also required for durability testing and guidelines for structural design with SHCC, which is the focus of follow-up committee activity in TC 240-FDS.
► For the first time water movement in cement-based materials could be quantified in a non-destructive way. ► neutron radiography has a sensitivity and a spatial resolution unknown so far. ► Results ...are essential for prediction of service life. ► Results will contribute to more durable and more ecological construction.
Service life of reinforced concrete structures is often limited by penetration of water and compounds dissolved in water into concrete. Concrete can be damaged in this way and corrosion of steel reinforcement can be initiated. There is an urgent need to study water penetration into concrete in order to better understand deterioration mechanisms and to find appropriate ways to improve durability. Neutron radiography provides us with an advanced non-destructive technique with high spatial resolution and extraordinary sensitivity. In this contribution, neutron radiography was successfully applied to study the process of water absorption of two types of concrete with different water–cement ratios, namely 0.4 and 0.6. The influence cracks and of water repellent treatment on water absorption has been studied on mortar specimens. It is possible to visualize migration of water into concrete and other cement-based composites and to quantify the time-dependent moisture distributions as function of time with high spatial resolution by means of neutron radiography. Water penetration depth obtained from neutron radiography is in good agreement with corresponding values obtained from capillary suction tests. Surface impregnation of concrete with silane prevents capillary uptake of water. Even fine cracks are immediately filled with water as soon as the surface gets in contact. Results provide us with a solid basis for a better understanding of deteriorating processes in concrete and other cement-based materials.
Service life and durability of reinforced concrete structures have become a crucial issue because of the economical and ecological implications. Service life of reinforced concrete structures is ...often limited by penetration of water and chemical compounds dissolved in water into the porous cement-based material. By now it is well-known that cracks in reinforced concrete are preferential paths for ingress of aggressive substances. Neutron radiography was successfully applied to study the process of water penetration into cracked steel reinforced concrete. In addition, the effectiveness of integral water repellent concrete to prevent ingress of water and salt solutions was investigated. Results are described in detail in this contribution. It will be shown that neutron radiography is a powerful method to visualize the process of water penetration into cracked and uncracked cement-based materials. On the basis of the obtained experimental data, it is possible to quantify the time-dependent water distributions in concrete with high accuracy and spatial resolution. It is of particular interest that penetration of water and salt solutions into damaged interfaces between concrete and steel can be visualized by means of neutron radiography. Deteriorating processes in cracked reinforced concrete structures can be studied in a completely new way. This advanced technology will help and find adequate ways to improve durability and service life of reinforced concrete structures. This will mean at the same time an essential contribution to improved sustainability.
Cosmogenic nuclides produced in quartz may either decay or accumulate while sediment is moved through a river basin. A change in nuclide concentration resulting from storage in a floodplain is ...potentially important in large drainage basins in which sediment is prone to repeated burial and remobilization as a river migrates through its floodplain. We have modeled depth- and time-dependent cosmogenic nuclide concentration changes for
10Be,
26Al, and
14C during sediment storage and mixing in various active floodplain settings ranging from confined, shallow rivers with small floodplains to foreland-basin scale floodplains traversed by deep rivers. Floodplain storage time, estimated from channel migration rates, ranges from 0.4 kyr for the Beni River basin (Bolivia) to 7 kyr for the Amazon River basin, while floodplain storage depth, estimated from channel depth, ranges from 1 to 25 m.
For all modeled active floodplain settings, the long-lived nuclides
10Be and
26Al show neither significant increase in nuclide concentration from irradiation nor decrease from decay. We predict a hypothetical response time after which changes in
10Be or
26Al concentrations become analytically resolvable. This interval ranges from 0.07 to 2 Myr and exceeds in all cases the typical residence time of sediment in a floodplain. Due to the much shorter half life of
14C, nuclide concentrations modeled for the in situ-produced variety of this nuclide are, however, sensitive to floodplain storage on residence times of <
20 kyr.
The cosmogenic nuclide composition of old deposits in currently inactive floodplains that have been isolated for periods of millions of years from the river that once deposited them is predicted to either increase or decrease in
10Be and
26Al concentration, depending on the depositional depth. These conditions can be evaluated using the
26Al/
10Be ratio that readily discloses the depth and duration of storage.
We illustrate these models with examples from the Amazon basin. As predicted, modern bedload collected from an Amazon tributary, the Bolivian Beni River, shows no systematic change in nuclide concentration as sediment is moved through 500 km of floodplain by river meandering. In contrast, in the central Amazon floodplain currently untouched by the modern river system, low
26Al/
10Be ratios account for minimum burial depths of 5 to 10 m for a duration of >
5 Myr.
The important result of this analysis is that in all likely cases of active floodplains, cosmogenic
10Be and
26Al concentrations remain virtually unchanged over the interval sediment usually spends in the basin. Thus, spatially-averaged denudation rates of the sediment-producing area can be inferred throughout the entire basin, provided that nuclide production rates are scaled for the altitudes of the sediment-producing area only, because floodplain storage does not modify nuclide concentrations introduced from the sediment source area.
At present several methods are available to predict the durability of reinforced concrete structures. In most cases, one dominant deterioration process such as carbonation or chloride penetration is ...taken into consideration. Experimental results as well as observations in practice show that this is not a realistic and certainly not a conservative approach. In order to test more realistically, RILEM TC 246-TDC, founded in 2011, has developed a method to determine the durability of concrete exposed to the combined action of chloride penetration and mechanical load. In this report, a test method is presented which allows determination of realistic diffusion coefficients for chloride ions in concrete under compressive or tensile stress. Comparative test results from five different laboratories showed that the combination of mechanical and environmental loads may be much more severe than a single environmental load without mechanical loading. Modelling and probabilistic analysis also showed that the obvious synergetic effects cannot be neglected in realistic service life prediction.
The external photoluminescence quantum yield of, for example, thin film semiconductors can be conveniently determined using the improved integrating‐sphere method (see Figure) presented here. ...Spectrally resolved detection allows the excitation source and the emission to be distinguished. The method will be particularly useful for samples with small Stocks' shifts or low photoluminescence quantum yields or for highly scattering samples. Fig
At an ocean margin site 37°S offshore Chile, we use the meteoric cosmogenic 10Be/9Be ratio to trace changes in terrestrial particulate composition due to exchange with seawater. We analyzed the ...marine authigenic phase in surface sediments along a coast‐perpendicular transect and compared to samples from their riverine source. We find evidence for growth of authigenic rims through coprecipitation, not via reversible adsorption, that incorporate an open ocean 10Be/9Be signature from a deep water source only 30 km from the coast, overprinting terrestrial 10Be/9Be signatures. Together with increasing 10Be/9Be ratios, particulate‐bound Fe concentrations increase, which we attribute to release of Fe‐rich pore waters during boundary exchange in the sediment. The implications for the use of 10Be/9Be in sedimentary records for paleodenudation flux reconstructions are the following: in coast‐proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater, whereas sites beneath well‐mixed seawater will preserve global flux signatures.
Key Points
Meteoric 10Be/9Be in marine sediments shows terrestrial signals overprinted by seawater ratios 30 km offshore Chile coast (37°S)
Net loss of reactive Fe and Be metals from pore water to sedimentary phase provides evidence for boundary exchange mechanism
Implications for 10Be/9Be in marine records for paleodenudation flux reconstructions are that exchange with seawater cannot be neglected
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