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Galvanic corrosion protection by embedded zinc anodes is an accepted technique for the corrosion protection of reinforcing steel in concrete. Galvanic currents flow between the zinc anode and the steel reinforcement due to the potential difference that is in the range of a few hundred mV. The ion distribution was studied on two steel reinforced concrete specimens admixed with 3 wt.% chloride/wt. cement and galvanically protected by a surface applied EZ-anode. On both specimens, a zinc anode was embedded and glued to the concrete surface by a geo-polymer-based chloride-free binder. At one specimen, the EZ-anode was operated for 2,5 years, the EZ-anode at the other specimen was not electrically connected to the reinforcement, this specimen serves as a reference. Both specimens have been stored under identical conditions. The ion distribution between the anode (EZ-ANODE) and cathode (steel reinforcement) was studied by laser-induced breakdown spectroscopy (LIBS) after 7 months, 12 months, and 2,5 years. Results of the LIBS studies on the specimen with activated EZ-anode after 7 months, 12 months, and 2,5 years and of the reference specimen after 2,5 years are reported. Results show that diffusion of ions contributes to the changes in the ion distribution but migration, especially of chlorides towards the EZ-anode is significant despite the weak electric field – several hundred millivolts generated by the galvanic current. Results show that chloride ions accumulate near the zinc-anode as in water-insoluble zinc-hydroxy chlorides Simonkolleit.

An important aspect with regard to the service life of zinc based galvanic anodes and the durability of the corrosion protection of steel in concrete is the “galvanic chloride extraction”. Chloride ions move in the electric field generated by the current, flowing between the galvanic anode and the cathodic steel. Migration leads to an accumulation of anions, e.g. chloride ions, at the anode and depletion of chlorides near the steel rebar surface. The ion migration was studied on steel reinforced concrete specimens admixed with 3 wt.% chloride/wt. cement and galvanically protected by a surface applied embedded zinc anode (EZA). The zinc anode was embedded and glued to the concrete surface by a geo-polymer based chloride free binder. The EZA was operated over a period of 1 year and the ion distribution between anode (EZA) and cathode (steel reinforcement) was studied by laser induced breakdown spectroscopy (LIBS) after 5 months, 7 months and 12 months. The results show that chloride ions efficiently migrate in the direction of the zinc-anode and accumulate there. Chloride distribution in the EZA correlates with the distribution of zinc ions generated by the anodic dissolution of the zinc anode in the binder matrix. The microstructure of the binder matrix and its interface to the zinc-anode are studied by REM/EDX – preliminary results will be reported.

Carbon-based conductive coatings are complex composites, consisting of an organic or inorganic binder and conductive carbon components, for application as anodes in impressed current cathodic protection systems of reinforced concrete structures. The electrochemical properties of three coatings at different humidity and in saturated calcium hydroxide solution were studied by electrochemical methods, such as electrochemical impedance measurement, measuring of open circuit potential over time and galvanostatic polarization. The dissolved organic and inorganic carbons in electrolyte solution were quantified by using a photometric method. The structures of the coatings were investigated before and after the electrochemical tests by microscopy and scanning electron microscope/EDX analysis. The results of the electrochemical impedance measurements show that the tested coatings all have a relatively low resistance, which is between 100 and 200V. The binder and the surface porosity influence the degradation behavior of those coatings. Especially the organic binder reacts with the strong alkaline medium under dissolving of organic carbon. [ABSTRACT FROM AUTHOR]

The reduction of the chromate contents in cements affects the electrochemical reactions of galvanized reinforcing steels in fresh concrete. By means of electrochemical measurements and bar pull-out tests the effect of chromates on the formation of protective coatings at the zinc and the bond behaviour have been investigated using chromate-containing and chromate-reduced cements. The results have shown that the bond zone was affected as a result of chromate reduction for cement types CEM I and CEM II. The disturbance to the bond zone should be considered as long-term in relation to the pore structure which is formed. The effects on the bond are largely compensated for as the concrete ages. The results of the related bond strength with displacement paths of 0.1 and 0.5 mm, respectively, are still within the range of expected figures for non-galvanized reinforcing steel despite the structural disturbance. Under practical aspects it is not necessary that the existing structural disturbance with respect to bond strength is taken into consideration. [ABSTRACT FROM AUTHOR]

The air contaminants are absorbed in a mixture of hydrochloric acid/acetic acid/water, the solution made basic, and the analytes extracted (as the corresponding diamine in the case of TDI). The trifluoroacetamide derivatives are then formed and measured by gasliquid chromatography. [ABSTRACT FROM PUBLISHER]

Objectives: To measure the concentrations of organochlorine (OC) pesticides in nursing mothers in Western Australia and to evaluate the safety of these concentrations for breast-fed infants; to evaluate the need for future monitoring of OC pesticide concentrations and to determine whether breast milk is an accurate substitute for adipose tissue in future monitoring programs., Design: Two cohorts of nursing mothers were recruited during the period October 1990 to March 1991. Levels of OC pesticides were measured in 128 samples of breast milk and 31 samples each of adipose tissue, maternal blood and cord blood. Laboratory analysis was by gas chromatography with electron capture. Health Department studies since 1974 were collated and levels of OC pesticides compared over time., Results: DDT (dichlorodiphenyltrichloroethane), HCB (hexachlorobenzene) and dieldrin were found in all samples of breast milk and adipose tissue. A significant fall in the levels of OCs was noted since the 1974 survey, with the current concentrations of the cyclodienes (heptachlor, chlordane and dieldrin) being close to the limit of detection of the assay. The acceptable daily intake for dieldrin was exceeded in 90% of infants and for heptachlor in 2% of infants. The daily intakes of the other OCs were below the respective acceptable levels. HCB was detected at a median level of 0.1 mg/kg in both breast milk and adipose tissue despite being deregistered in 1972. As there is no current acceptable daily intake for HCB, the safety of this level could not be assessed by this method. A low correlation was found between levels of the cyclodiene pesticides in breast milk and adipose tissue, but levels of DDT and HCB were closely correlated., Conclusions: Restrictions on the use of the OC insecticides (DDT, aldrin, dieldrin, heptachlor and chlordane) have resulted in reduced concentrations of these chemicals in breast milk and adipose tissue as compared with previous studies. The dieldrin intake of breast-fed infants consistently exceeded the acceptable daily intake; the heptachlor intake exceeded the acceptable daily intake in some infants, but the low concentrations of heptachlor in breast milk made accurate measurement difficult. The concentrations of DDT and chlordane in breast milk did not pose a hazard to breast-fed infants. The significance of the levels of the fungicide HCB in breast milk cannot be determined. The widespread distribution of HCB, its marked persistence in the environment and its potential for human toxicity indicate a need for continued monitoring, for which breast milk is a suitable medium. The poor correlation between concentrations of dieldrin, heptachlor and chlordane in breast milk and adipose tissue may reflect the technical difficulty of measuring chemical concentrations close to the limit of detection. As aldrin is a registered pesticide and the dieldrin intake of breast-fed infants is consistently above the acceptable daily intake, monitoring of dieldrin should continue. Further population monitoring of DDT, heptachlor and chlordane is unlikely to be of value.

The changes in concentration of heptachlor epoxide (HCE) and oxychlordane (OCD) were studied in the tissues of beef cattle that had previously grazed pasture contaminated with commercial heptachlor. In 25 cows and heifers monitored over 488 days, the mean concentration of HCE decreased from 22.0 to 0.08 mg/kg and of OCD from 5.68 to 0.18 mg/kg. The respective half-lives were estimated to be 66 and 92 days. In a controlled feeding experiment, nine steers were subjected to one of three dietary regimes; a high plane of nutrition for 81 days then a low plane for 140 days; a moderate plane of nutrition for the total period; and a low plane of nutrition for 81 days then a high plane for 140 days. Approximately five months later similar treatments were applied for 101 and 94 days. The rate of decline of HCE and OCD was consistently greatest in animals on the high plane of nutrition and lowest in those on the low plane. Lactation did not appear to have a major effect on the rate of decline in the tissue concentrations of these compounds. No significant (P greater than 0.05) relationships were found between the concentrations of HCE or OCD in the subcutaneous fat and either milk or blood at any stage of the experiment. At slaughter, from 18 to 24 months after the commencement of the experiments, significant correlations (P less than 0.05) were found among concentrations of HCE and OCD in subcutaneous fat, renal fat and fat from the bone marrow.(ABSTRACT TRUNCATED AT 250 WORDS)