Threshold Chloride Concentration Research Articles

Reliability Approach to Service Life Prediction of Concrete Exposed to Marine Environments

In the life of concrete structures they are subjected to external actions or agents that in time may alter them from a safe state to failure or a damage state. One of the processes that may trigger the onset of corrosion of steel embedded in concrete is the ingress of chloride ions that eventually reach the reinforcement, causing the rupture of the passive film. In this paper, a method is proposed for interpretation of immersion test results and prediction of the service life of concrete structures exposed to chloride ions. Once the chloride profiles are determined after the immersion test, a realization of the random diffusion coefficient is obtained at each point for which there is a measurement of the chloride content. These samples are used to predict the probability density function of the diffusion coefficient. A reliability analysis is subsequently performed for 10 different lightweight high-strength concrete mixes. A reinforced concrete element is considered to have failed when corrosion initiates at the reinforcement, i.e., after a certain chloride concentration threshold is reached at the reinforcement. The probability of corrosion initiation in time is computed for some of the concrete mixes examined.

Factors affecting threshold chloride for reinforcement corrosion in concrete

Three cements with variable C 3A contents were mixed with different levels of chloride, alkali and sulfate contents to study the effect of these parameters on pore solution composition. Effect of exposure temperature was also studied by curing the chloride-treated specimens at 20 ° and 70 °C. Pore solution was extracted using a high pressure pore solution extrusion device and analysed for chloride and hydroxyl ion concentrations. Threshold chloride for onset of reinforcement corrosion was computed using threshold [ Cl − OH − ] ratio of 0.3. The results showed that C 3A content and exposure temperature have very strong influence on threshold chloride content. Alkali content of cement has marginal effect whereas presence of sulfates along with chlorides has moderate effect on the threshold chloride content.

Chloride attack of reinforced concrete: an overview

The mechanism of chloride-induced corrosion of steel embedded in concrete, the ingress of chlorides into the concrete, and the threshold chloride content for corrosion to occur are discussed. The binding of chloride ions by cement compounds and the associated effect of using different cements, both Portland and blended, as well as other factors influencing corrosion, are considered. Tests for the penetrability of concrete to chlorides are described. Finally, the prevention of corrosion is discussed.

Assessment of the toxicity of an industrial effluent with a two-generation reproduction test using Daphnia magna

The toxicity of an industrial effluent and solutions of its main component, CaCl 2, was assessed with acute and chronic toxicity tests with Daphnia magna. EC 50 values were not different until after 96 h when the effluent proved more toxic than the pure CaCl 2, In the first generation of the chronic tests, reproduction was decreased at the same threshold chloride concentration for both the pure CaCl 2, and the effluent. In the second generation, reproduction returned to control levels in all tested CaCl 2, concentrations. The effluent, however, decreased the reproduction even at a dilution corresponding to one-tenth of the 96-h EC 50, a dilution at which all effluent components are within European water quality standards. This difference in chronic toxicity between the effluent and the CaCl 2 solutions could not have been foreseen with 48 h acute tests or one-generation reproduction tests, which are the standard ecotoxicological testing procedures. Expanding the reproduction tests to two generations revealed important information on chronic toxicity that could add to an increased cost-effectiveness in the treatment of the effluent.

Effect of cement composition on chloride binding and corrosion of reinforcing steel in concrete

Pore solution study has been carried out on 2.43 and 14% C 3A hardened cement pastes. Data have been analyzed in conjunction with the data developed in two pore solution studies made by Page and Vennesland and Diamond using 7.37 and 9.1% C 3A mature cement pastes. The results show that C 3A and alkali contents of a cement have significant effect on its chloride-binding capacity. For similar alkali content, the levels of free chlorides in the pore solutions of 2.43 and 9.1% C 3A cement pastes are respectively 4.7 and 2.8 times more than in a 14% C 3A cement. The alkali content of a cement appears to have an inhibiting effect on its chloride-binding capacity. However, this effect is overshadowed by a conjoint strong elevation of the OH − ion concentration in the pore solution due to cement alkalies, causing a net lowering of the Cl −/OH − ratio which roughly ascertains corrosion risk. Threshold chloride values have been evaluated for different C 3A cements. The threshold chloride content for a typical Type I portland cement with C 3A upto 8% and Na 2O equivalent upto 0.60%, may be taken as 0.4% chlorides by weight of cement. However, for a similar alkali cement with a high C 3A content of about 14%, the chloride threshold value is 2.5 times higher and may be taken as 1.0% by weight of cement.

Pore Solution Composition and Chloride Effects on the Corrosion of Steel in Concrete

Abstract The corrosion mechanism of steel in concrete and the so-called threshold chloride content are discussed based on the results obtained by electrochemical measurement, pore solution analysis, and scanning electron microscopy (SEM) observation. It is shown that mortar (or concrete) provides better protection to steel than alkaline solutions. One of the protective mechanisms provided by mortar is found to be the pH control action of calcium hydroxide crystals located at the steel-mortar interface. For the protective mechanisms provided by mortar to operate, adhesion between the steel and the mortar is necessary and formation of voids at the steel-mortar interface is essential for active corrosion to start. The critical threshold chloride content is not determined simply by a parameter of the pore solution such as [Cl−]/[OH−] ratio; it is shown that the threshold value depends on the steel-mortar interface conditions.

The electrochemical behaviour of INCOLOY 800 and AISI 304 steel in solutions that are similar to those within occluded corrosion cells

Occluded corrosion cell solutions were synthesized by a mixture of iron, nickel and chromium chloride salts, the concentration of which was proportionally the same as that of the alloy matrix. The overall chloride concentration varied between 0.01 and the saturation of one of these salts. The variation of open-circuit electrode potential and of the potential-dynamic anodic polarization curves with increasing overall chloride concentration indicated that the corrosion behaviour of INCOLOY 800 and AISI 304 steel changes from the passive to the active dissolution corrosion mechanism. The threshold chloride concentration is close to 0.5 g ion 1−1 for both alloys. It was noticed that, even for a very concentrated medium, the dissolution rate was independent of mass transport. It was also found that the anodic behaviour of these alloys depended essentially on the chloride concentration and pH of the solution. Hence, an acidified NaCl solution, which is much easier to prepare than a synthetic occluded corrosion cell solution, can be used in kinetic studies on the propagation of localized corrosion.

Differential sensitivity to angiotensin II in pregnant rabbits

Threshold concentrations for angiotensin II and barium chloride were determined in the perfused hind limb of the nonpregnant, pseudopregnant, and pregnant rabbit. The threshold concentration for these vasoconstrictors was defined as the amount of drug per milliliter of hind limb blood flow which would increase hind limb blood pressure by 4 mm Hg. There was no difference in the mean angiotensin II threshold concentration between the nonpregnant and pseudopregnant rabbits. The angiotensin II dose for the pregnant rabbits was double that of the first two groups. There was no significant difference in the mean barium chloride threshold concentration between the three groups. This difference in the pregnant angiotensin II threshold concentration with no difference in barium chloride threshold concentration indicates a change in vascular sensitivity which is dependent upon a specific angiotensin II-receptor interaction and is not inherent in the contractile response of the vessel, nor is it mimicked by pseudopregnancy.

Méthodes de conservation d'objets de fouilles en fer. Etude quantitative comparée de l'élimination des chlorures

Abstract The Laboratory of the Musee d'art et d'histoire, Geneva, has been concerned with the problem of conserving excavated iron objects, often very corroded. In the search for a satisfactory method of desalination, the alkaline sulphite treatment developed by North and Pearson for marine objects was studied. Within the framework of a quantitative study of chloride elimination, this was compared with five other methods. Further researches were undertaken on the quantitative distribution of chlorides in a corroded iron object, the quantity of chlorides remaining after different treatments, the chloride concentration threshold at which corrosion starts and becomes dangerous.