Environmental Chloride Concentrations Research Articles

Corrosion mechanism and damage characteristic of steel fiber concrete under the effect of stray current and salt solution

Steel fiber reinforced concrete (SFRC) has been widely used in construction and transportation due to its superior mechanical properties. From the perspective of structure, SFRC is a potential solution to the problem of stray current induced corrosion in electrical railway systems. However, the corrosion mechanism of SFRC under the coupling effect of stray current and salt solution is not clear, and the change of mechanical properties in the process still lacks a quantitative description, so it is difficult to predict the structural life. In this paper, different corrosive media were selected for the stray current induced corrosion test of SFRC, in which the chloride concentration was adjusted to study its influence on the corrosion rate. Ultrasonic and electric current were combined to monitor the corrosion process. The colorimetric and titration method were used to measure the chloride depth and concentration in the specimen after corrosion, mercury intrusion porosimetry was employed to determine the pore structure. It is found that chloride is the most destructive to SFRC and dominates the corrosion process, while sulfate and caustic alkali contribute secondary effect. Chloride destroyed the passive film on the surface of the steel fiber and corroded it to form a local rust expansion area, causing concrete damage and reducing mechanical properties. In addition, if the damage degree reaches 0.3 ∼ 0.4, the structure will be destroyed. When the environmental chloride concentration reaches the threshold 0.6 mol/L, the higher the concentration, the faster the SFRC corrosion. The quantitative relationship between the main influencing factors (concentration of chloride, corrosion time and chloride penetration depth) and damage degree is proposed based on the experimental data. The research may provide reference for the application of SFRC in electric railway projects.

An experimental study on durability of shield segments under load and chloride environment coupling effect

Taking into consideration a shield tunnel’s environmental and mechanical properties, we designed a durability test method for its segment lining under the coupling effect of load and chloride environment (CEL&E). To verify the credibility of the method, we developed an environmental simulation test device and conducted durability tests on specimens using the test device. The results of the tests showed that with increased environmental chloride concentration and extended time period, the chloride ion content in the protective layer of the concrete increased gradually. It was also found that the external load changed the pore structure properties within the concrete, thus affecting chloride ion penetration. Considering that the load effect can change the structural characteristics of pores, we proposed a chloride diffusion coefficient evolution model for concrete under the CEL&E. By applying numerical fitting and using parameters of quadratic regression, we also established an equation for determining surface ion concentration under the coupling effect. Finally, we devised an evaluation model and calculation method for durability of a shield tunnel’s segment lining under the CEL&E. This calculation method can be used for assessing the concrete durability of existing shield tunnel structures, prediction of remaining service life, as well as durability design of new shield tunnel structures.

Ameliorating Effect of Chloride on Nitrite Toxicity to Freshwater Invertebrates with Different Physiology: a Comparative Study Between Amphipods and Planarians

High nitrite concentrations in freshwater ecosystems may cause toxicity to aquatic animals. These living organisms can take nitrite up from water through their chloride cells, subsequently suffering oxidation of their respiratory pigments (hemoglobin, hemocyanin). Because NO(2)(-) and Cl(-) ions compete for the same active transport site, elevated chloride concentrations in the aquatic environment have the potential of reducing nitrite toxicity. Although this ameliorating effect is well documented in fish, it has been largely ignored in wild freshwater invertebrates. The aim of this study was to compare the ameliorating effect of chloride on nitrite toxicity to two species of freshwater invertebrates differing in physiology: Eulimnogammarus toletanus (amphipods) and Polycelis felina (planarians). The former species presents gills (with chloride cells) and respiratory pigments, whereas in the latter species these are absent. Test animals were exposed in triplicate for 168 h to a single nitrite concentration (5 ppm NO(2)-N for E. toletanus and 100 ppm NO(2)-N for P. felina) at four different environmental chloride concentrations (27.8, 58.3, 85.3, and 108.0 ppm Cl(-)). The number of dead animals and the number of affected individuals (i.e., number of dead plus inactive invertebrates) were monitored every day. LT(50) (lethal time) and ET(50) (effective time) were estimated for each species and each chloride concentration. LT(50) and ET(50) values increased with increases in the environmental chloride concentration, mainly in amphipods. Results clearly show that the ameliorating effect of chloride on nitrite toxicity was more significant in amphipods than in planarians, likely because of the absence of gills (with chloride cells) and respiratory pigments in P. felina. Additionally, this comparative study indicates that the ecological risk assessment of nitrite in freshwater ecosystems should take into account not only the most sensitive and key species in the communities, but also chloride levels in the aquatic environment.

Toxicity of Ammonia and Nitrite to the Gila Trout

Abstract A pilot study was conducted to determine the acute resistance of Gila trout Oncorhynchus gilae to ammonia (NH3) and nitrite (NO− 2). All fish survived exposure to up to 4.5 mg/L total NH3-N (0.36 mg/L un-ionized NH3-N; pH 8.5, 15°C) for 96 h. The 96-h median lethal concentration was 5.86 mg/L total NH3-N (0.47 mg/L un-ionized NH3-N). Gila trout exposed to nitrite for 96 h died when exposed to 10 mg/L or more NO− 2-N and 3 mg/L environmental chloride. Increasing the environmental chloride concentration increased survival.

Spatial and temporal variability of ground water recharge in central Australia: a tracer approach.

Two environmental tracer methods are applied to the Ti-Tree Basin in central Australia to shed light on the importance of recharge from floodouts of ephemeral rivers in this arid environment. Ground water carbon-14 concentrations from boreholes are used to estimate the average recharge rate over the interval between where the ground water sample first entered the saturated zone and the bore. Environmental chloride concentrations in ground water samples provide estimates of the recharge rate at the exact point in the landscape where the sample entered the saturated zone. The results of the two tracer approaches indicate that recharge rates around one of the rivers and an extensive floodplain are generally higher than rates of diffuse recharge that occurs in areas of lower topographic relief. Ground water 2H/1H and 18O/16O compositions are all depleted in the heavier isotopes (delta2H = -67 per thousand to -50 per thousand; delta18O = -9.2 per thousand to -5.7%o) compared with the long-term, amount-weighted mean isotopic composition of rainfall in the area (delta2H = -33.8 per thousand; delta18O = -6.3 per thousand). This indicates that recharge throughout the basin occurs only after intense rainfall events of at least 150 to 200 mm/month. Finally, a recharge map is developed to highlight the spatial extent of the two recharge mechanisms. Floodout recharge to the freshest ground water (TDS <1,000 mg/L) is approximately 1.9 mm/year compared with a mean recharge rate of approximately 0.2 mm/year to the remainder of the basin. These findings have important implications for management of the ground water resource.

Acute toxicity of nitrite to crayfish Procambarus simulans in varied environmental conditions

In low chloride (≤5 mg litre −1), neutral pH water, resistance times to 50% death of crayfish Procambarus simulans to environmental nitrite concentration were highly significantly correlated (r = -0·953) in an inverse, double logarithmic fashion. The best fit regression equation equalled: log time ( h) = 2·64−0·84 log nitrite concentration (mg litre −1). This model predicts resistance times to 50% death for 24,48, 72 and 96 h of 31·5, 13·8, 8·6 and 6·1 mg of nitrite litre −1. Increases in environmental chloride concentration to 300 mg litre −1 ameliorated the toxicity of nitrite. At a lower pH (5·6) resistance times decreased slightly and the protective efficacy of chloride ions was reduced. These results indicate that P. simulans possesses an intermediate tolerance of nitrite relative to fish species and that chloride ions act as antagonists to nitrite ions (NO 2 −) at monovalent ion uptake sites, but apparently do not compete with the uptake of the uncharged nitrous acid (HNO 2) molecule.

SALT AND WATER ANATOMY, CONSTANCY AND REGULATION IN RELATED CRABS FROM MARINE AND TERRESTRIAL HABITATS

1. Exposure to environmental salinities ranging from 120 to 720 mM. Cl/L. for 72 hours did not produce changes in fresh weights of the land crab (Gecarcinus lateralis), the ghost crab (Ocypode albicans) or the mangrove crab (Goniopsis cruentatus). There was an increase in weight of questionable significance after 24 hours in crabs exposed to distilled water. Only in distilled water was there any change in the blood specific gravity of ghost crabs. Even this change was of questionable significance.2. The total body water content of ghost crabs is significantly larger than those of land crabs and mangrove crabs, which are similar. The fractions of total water content which are available for the dilution of thiocyanate and inulin are similar in the three species. The volumes available for the dilution of inulin are about two-third the volumes in which SCN appears to be diluted. This suggests the interesting possibility of a functionally closed, lumen flow, circulation.3. The blood chloride concentration of m...