不同因素下钢筋混凝土电化学除氯效率研究

采用2 A/m²的电流密度、饱和氢氧化钙溶液、不锈钢网对钢筋混凝土试件进行电化学除氯实验，研究除氯时间、粉煤灰掺量、减水剂、引气剂对电化学除氯效率及残留Cl^-含量的影响。结果表明：除氯效率随通电时间增长而提高；掺10%与20%粉煤灰的试件28 d除氯效率分别为56.9%与54.3%，粉煤灰掺量的增加对除氯效率无明显增益；经28 d除氯，掺入减水剂试件比普通组除氯效率下降约10%；掺引气剂除氯效率约75.1%。除氯后，Cl^-集中在距试件表面15~35 mm的范围内，钢筋附近Cl^-含量大幅下降。经试件钢筋锈蚀电位测量可见，除氯时电位负向增大，除氯一段时间后电位正向移动，逐渐达到钝化电位。     

Chloride threshold for corrosion of galvanized reinforcement in concrete exposed in the mexican Caribbean

The time of incubation (TI) and chloride threshold (CT) necessary to initiate corrosion of reinforcement steel are crucial variables to predict the useful life of an infrastructure in any model. For black steel there is a great amount of data in the bibliography. However, for galvanized steel, is very scarce and in tropical climates no data exist. In this research, CT and TI were determined for galvanized steel embedded in concretes with water/cement (w/c) ratios of 0.4, 0.5, 0.6, and 0.7. The samples were corroded under natural conditions in the north coast of the Yucatan Peninsula for nine years. The results show that galvanized reinforcement can resist chloride levels 2.6–3 times higher than black steel, even in poor quality concretes. Likewise, it was possible to observe that TI for galvanized steel is twice that of black reinforcement, and so the former offers the possibility of extending the useful life of structures.     

Effect of water and chloride contents and carbonation on the electromagnetic characterization of concretes on the GPR frequency band through designs of experiment

Water content, chloride content and carbonation are three durability indicators that affect not only concrete properties and integrity, but also the ground penetrating radar (GPR) response. This article characterizes the effect of water and chloride contents as well as carbonation on the high-frequency electromagnetic (EM) properties of concretes using a coaxial-cylindrical cell operating within the large frequency band from 50 MHz to appprox. 1000 MHz, thus making possible to study dispersion effects on the complex relative permittivity of various concretes.During a second step, three specific designs of experiment (DoE), involving water and chloride contents, and then carbonation, are designed and studied in order to establish the relative sensitivity of these parameters compared to others in describing the mixes at three different frequencies.The complex dielectric properties are evaluated in the laboratory on many concrete specimens (numbering 24, 36 and 24 for the moisture, chloride and carbonation studies respectively). For these evaluations, the composition parameters consist of nature of aggregate, nature of cement, cement content and water-to-cement ratio (W/C) while conditions are described by degree of water saturation, chloride content or carbonation. In the case of the chloride and carbonation DoEs, the mixes are tested under both dry and saturated conditions.The models describing complex relative permittivity, in association with the designs of experiment, are multi-linear polynomials of the 4 or 5 identified engineering parameters, to be chosen depending on the study. The interpretation of datasets entails in independent calculation of model coefficients for the real and imaginary parts of relative permittivity, at the three chosen frequencies. This approach reveals the significant relationships existing between dielectric properties and composition parameters as well as their evolution versus frequency.The major results of this work can be summarized as follow:

• -The degree of water saturation amounts to about 80% on ε′_r variability and 60% to 15% versus frequency on ε″_r variability, for the first campaign.
• -The chloride content, while only visible in saturated mixes, represents approx. 40% and 50% with porosity (via the W/C ratio) accounting for some 30% and 40% on ε′_r and ε″_r variabilities, respectively.
• -Lastly, carbonation, while also only visible in saturated mixes, corresponds to a weight of about 14% in low frequencies and vanishes at high frequencies for ε′_r variability; this amount rises to roughly 24% for ε″_r variability.

     

混凝土抗氯离子渗透扩散性研究

采用快速氯离子渗透试验方法、稳态电迁移方法和电导方法，对普通水泥混凝土、轻骨料混凝土及掺粉煤灰、矿渣、硅粉、偏高岭土和稻壳灰的混凝土进行了氯离子渗透扩散性试验研究。结果表明，混凝土的抗氯离子渗透扩散能力随水灰比的减小而提高。粉煤灰和矿渣能提高混凝土的抗氯离子渗透扩散能力，硅粉、偏高岭土、稻壳灰和适当掺量的矿渣能大幅度提高混凝土的抗氯离子渗透扩散能力。在整个通电量范围内，通电量和初始电流之间并不存在良好的线性关系。     

Corrosion resistance of low‐nickel duplex stainless steel rebars

The use of stainless steel bars in reinforced concrete structures may be an effective method to prevent corrosion in aggressive environments where high amounts of chlorides may penetrate in the concrete cover. For an estimation of the service life of structures where stainless steel bars are used, the chloride threshold for these rebars should be defined, and the influence of chemical composition and metallurgical factors that may affect the corrosion resistance (strengthening, welding, etc.) should be assessed. To reduce the cost of stainless steel reinforcement, duplex stainless steels with low nickel content have been recently proposed as an alternative to traditional austenitic steels, even though, few results are available regarding their corrosion performance in chloride contaminated concrete. This paper deals with the corrosion resistance of low‐nickel duplex stainless steel rebars (1.4362 and 1.4162) as a function of the chloride content. Comparison is made with traditional austenitic steels. An attempt to define a chloride threshold for the different stainless steels is made by comparing the results of several test procedures both in concrete and in solution.     

Detection and identification of concrete cracking during corrosion of reinforced concrete by acoustic emission coupled to the electrochemical techniques

The tenacious oxide passive film, which is formed on the surface of embedded reinforcing steel under high alkaline condition of concrete, protects the steel against corrosion. However, the condition of passivity may be destroyed, due to processes such as leaking out of fluids from concrete, atmospheric carbonation or through the uptake of chloride ions. Passive steel reinforcing corrosion induced by chloride is a well-known problem, especially where chloride-containing admixtures or chloride contaminated aggregate are incorporated into the concrete. The objective of this work is on one hand to study the effect of chloride ions on passivity breakdown of steel, respectively, in simulated concrete pore solution (SCP) and in concrete reinforcement, and on the other hand to reproduce the carbonation phenomena by applying to the concrete samples a heating–cooling cycles. In this context, the acoustic emission coupled to the electrochemical techniques (potentiodynamic and electrochemical impedance spectroscopy (EIS)) are used.

The results show clearly that [Cl⁻]/[OH⁻] ratio of 0.6 is the critical threshold where the depassivation set-up can be initiated. In addition, the carbonation process is very aggressive with chloride ions and shows a perfect correlation with acoustic emission evolution.

A physical model of the reinforcement/electrolyte interface is proposed to describe the behavior of the reinforcement against corrosion in chloride solution.     

Comparative Study of Factors Influencing the Action of Corrosion Inhmitors for Mild Steel in Neutral Solution: II. Potassium Chromate

Abstract

The action of potassium chromate as a corrosion inhibitor for mild steel in neutral aqueous solution has been studied in relation to the surface preparation of the steel, the presence of aggressive salts in the solution, and temperature.

Surface preparation of mild steel has little effect on the minimum concentration of chromate required for protection in distilled water. In solutions containing aggressive anions a linear relation exists between the logarithm of the chromate concentration and the logarithm of the maximum concentration of aggressive anion that will permit inhibition. In solutions of low chromate concentration, up to 10^?1M, the order of aggressiveness of anions is chloride > sulphate > nitrate; the order changes at chromate concentration above 10^?1M to chloride > nitrate > sulphate. Corrosion in non-inhibiting chromate/aggressive anion solutions is always of a localised nature but is usually stifled, thus not leading to ‘dangerous’ attack. A 5-fold increase in chromate requirement for inhibition of abraded mild steel in distilled water is found between 5° and 60°, with a further large, rather indeterminate, increase above 60°.     

Investigation on the effectiveness of the repair method 8.3 “Corrosion protection by increasing the electrical resistivity” in chloride-containing concrete Part 3: The influence on corrosion of chloride-contaminated concretes under protective coatings

With the implementation of the repair method “increasing the electrical resistivity by coating” (MR 8.3), no direct repassivation of the reinforcing steel is initially intended. The success of the repair is rather linked to the change of the corrosion-relevant parameters over time. These include an increase in the concrete resistivity due to dehydration and gradual decrease in corrosion currents and driving voltages on the reinforcing steel. Within the scope of a research project funded by the German Research Foundation (DFG), application limits for the repair principle W-Cl could be defined. The chloride content present in the concrete at the rebar is the significant limiting factor for the application. While the corrosion activity even with moderately dehydrated specimens under diffusion-retarding coatings at chloride contents of 1 wt% Cl⁻/c is in the range of the passive current density, this cannot be generally determined for chloride contents of 2 wt% Cl⁻/c. The type of coating has a decisive influence on the dehydration of the concrete. For example, less dense concretes under a permeable coating (acrylic dispersion/OS 4) can dry out to such an extent that the passive current density is reached. With semipermeable coatings and the presence of high chloride contents of 2 wt% Cl⁻/c, the repair principle W-Cl does not lead to success according to the available test results.     

Evaluation of chloride contamination in concrete using electromagnetic non-destructive testing methods

We present the results of the sensitivity of some electromagnetic non-destructive testing (NDT) methods to chloride contamination. The NDT methods are resistivity, using a quadripole probe, capacitive technique, with few sets of electrodes, and radar technique, using different bistatic configurations. A laboratory study was carried out involving three different concretes with different water to cement ratios. The concretes were conditioned with different degrees of NaCl saturation by means of three solutions containing 0 g/L, 30 g/l or 120 g/l. The solution was homogenized in the concrete by using a specific procedure. Results show that the EM techniques are very sensitive to the chloride content and saturation rate and, on a second level, to the porosity. Multi-linear regression processing was performed to estimate the level of sensitivity of the NDT measurements to the three indicators. Values of ten ND observables are presented and discussed. At last, the uncertainties of the regression models are studied on a real structure in a tidal zone.     

混凝土保护涂层抗氯离子渗透性研究

在NaCl溶液中对混凝土保护涂层进行干/湿循环加速腐蚀实验,用电化学循环极化法和高压渗水法对混凝土保护涂层的防护效果进行了研究,并将两种方法研究结果进行对比.结果表明：氯盐环境中,混凝土保护涂层可以有效提高混凝土的抗渗性,降低氯盐对钢筋的腐蚀破坏;循环极化测试法可用于研究钢筋钝化膜的溶解特性和钢筋的锈蚀趋势.      

Effect of curing temperature on corrosion of steel bars embedded in calcium aluminate mortars exposed to chloride solutions

Important corrosion problems have been detected in reinforced concretes made of calcium aluminate cement (CAC). However, very little research has been performed to evaluate the incidence of the use of such cement on the corrosion process. Reinforced mortar specimens, pre-mixed with or without 4% NaCl of weight of cement, cured at 20° C, 40° C and 60° C for two weeks and immersed in either a 0.5 M or a 1.5 M NaCl solution, or kept in plastic bags for 255 days, have been monitored electrochemically. Corrosion potential, corrosion intensity and ohmic drop were recorded over time. The appearance with time of chloroaluminates has been monitored by X-ray diffraction, and its microstructure has been observed by means of back-scattering electron (BSE) microscopy. The reaction of chloroaluminates formation in reinforced concrete deals with the process of immobilising chloride ions which penetrate through the concrete up to the reinforcement. Therefore, the enhancement of such a reaction would be a way to reduce chloride ions in the pore solution contained in the concrete pores. Furthermore, stable chloroaluminates formation could mean a decrease in the risk of corrosion. Thus, corrosion rate measurements were carried out throughout the testing period to evaluate this point. Aluminous hydrates showed a high capacity to react with chloride ions to form chloroaluminates; however, the remaining chloride ions in the pore solution were still in an amount enough to promote reinforcement corrosion over time. Corrosion rate was found to be directly influenced by the curing temperature and, therefore, by the degree of conversion from hexagonal to cubic phases.     

Experimental investigation on chloride diffusion and binding in concrete containing metakaolin

In this paper, the effects of metakaolin addition on the compressive strength and chloride penetrability were studied. The study focused on the diffusion of the free and total chloride in concrete containing metakaolin (MK), which was measured by a potentiometric titration measurement. Effect of MK and sulphate on chloride binding capability was investigated, and Friedel’s salt was identified by X-ray diffraction and differential scanning calorimetry. The compressive strength increased with the addition of MK. Metakaolin decreased both the permeability of concrete and the free chloride, and increased the chloride binding capability greatly. The mechanism is that MK reduced the porosity and optimised the pore structure. The addition of MK favoured the formation of Friedel’s salts. However, sulphate decreased the chloride binding capability of concrete containing MK due to the formation of ettringite.     

Reinforced concrete structures – shall concrete remain the dominating means of corrosion prevention?

The acknowledged serious deterioration of reinforced concrete structures due to chloride induced corrosion has been the main fuel for research and development of very dense and impermeable concrete, so‐called high performance concrete (HPC). This development has dominated concrete research up through the 80'ies and 90'ies. The results have technically been successful. However, the practical use of such concretes on site have often posed serious difficulties, resulting in at times very low performance concrete structures although HPC was specified. The discrepancy between concrete quality reached in the laboratory, what is being specified in the design and what can realistically be achieved on site is seldom in balance. Alternative means of more or less reliable means of corrosion prevention, often based on organic materials, have during recent years been developed to protect our inorganic concrete and reinforcement. However, a highly reliable means of corrosion prevention has been the introduction of stainless steel reinforcement, which is available with dimensions and strengths directly interchangeable with ordinary carbon steel reinforcement. It has been proven that stainless steel and carbon steel can be in metallic contact when cast into concrete, without causing galvanic corrosion. This seems, for the present, to be like an unexpectedly simple and highly reliable solution to the corrosion problems. As exemplified, this technology is rapidly gaining momentum in highly corrosive environments – and concretes being much more robust to execution can now take over from HPC.     

自动电位滴定仪测定水中氯离子的探讨

通过使用自动电位滴定仪标定硝酸银标准溶液和测定工业循环水中氯离子的实验研究,总结了在使用中应注意的电极的维护保养和滴定终点设定方面的一些规律,结果表明用该仪器测定水中氯离子,其准确性和精密度均可获得满意的结果。     

Beitrag zur Spannungsrißkorrosion austenitischer Stähle

Contribution to the problem of stress corrosion cracking of austenitic steels It is shown on the basis of a stress corrosion cracking theories that the incubation phase is the factor determining the useful life of an element because in this phase protective layers are destroyed and crack nuclei are formed. Testing corrosion susceptibility in boiling magnesium chloride solution has the shortcoming that the solution is highly aggressive so that minor changes of the surface condition which may yield a considerable improvement of material behaviour in less aggressive conditions do not come to bear. Another shortcoming of MgC1₂ testing are divergent literature data concerning concentration so that there is also a scatter of boiling temperatures which has a pronounced influence on test results. Likewise an important role can be attributed to foreign ions and silicates from glas in the solution. It is more advantageous to use less concentrated solutions (up to 35%) because they enable clear current density potential curve to be obtained. An important factor concerning the test method is the previous investigation of specimens with a view to a residual stresses due to cold reduction. Under certain conditions the time to failure may be longer under cycling loads.     

Role of complexes in inhibition of mild steel by zinc–1-hydroxyethylidene-1, 1-diphosphonic acid mixtures

Abstract

The action of 1-hydrox yethylidene-1, 1-diphosphonic acid (HEDP) in combination with zinc ions as a corrosion inhibitor for mild steel in oxygen containing aqueous solutions has been investigated in relation to the presence of different zinc levels, the presence of aggressive anions, and different pH values. The highest inhibition effect was obtained at a 2·7:1 zinc/HEDP molar ratio, corresponding to 60 ppm zinc, and was associated with a significant anodic effect. In the absence of chloride and with no free forms of the inhibitor components, the zinc-HEDP mixture exhibited good protection over a wide range of pH (6·5-9·5). However, in a weakly acidic medium, protection could not be achieved. Calculations based on the dissociation constants of the HEDP and the stability constants of the possible zinc-HEDP complexes showed that this inhibition can be attributed to the presence of the 2:1 zinc-HEDP complex (Zn₂H_-1L^-) at a sufficient level. It is found that this anionic complex can behave as an anodic, passivating, inhibitor at a concentration as low as 0·00015M (20 ppm zinc-32 ppm HEDP mix ture). This passivity is prevented by the presence of sufficient chloride. The critical chloride concentration in these studies is approximately ten times higher than the complex concentration, in molar terms. It is also found that free phosphonate is aggressive and can prevent passivity due to the preferential formation of soluble iron-HEDP complex. The tolerance of the 2:1 complex to free phosphonate is substantially less than to chloride, approx imately equimolar.     

Environmental factors affecting the corrosion behavior of reinforcing steel III. Measurement of pitting corrosion currents of steel in Ca(OH)2 solutions under natural corrosion conditions

Using a simple electrolytic cell, the pitting corrosion current of reinforcing steel is measured in Ca(OH)₂ solutions in presence of chloride and sulfate as aggressive ions. Pitting corrosion current starts to flow after an induction period which depends on the concentration of both the aggressive and the passivating anions. The pitting corrosion current densities reach steady-state values which depend also on the type and concentration of the corrosive and passivating anions. The corrosive action of the aggressive species decreased in the order: SO₄²⁻ > Cl⁻. Corrosion of the steel is found to be governed by a single electron transfer reaction. Raising the temperature decreases the induction period associated with pit initiation and increases the corrosion current associated with pit propagation. From Arrhenius plots, the activation energies for both pit initiation and pit propagation in presence of chloride and sulfate ions are calculated.     

Damage to paint coatings caused by electrolyte immersion as observed in situ by scanning electrochemical microscopy

Damage to paint coatings caused by immersion in aqueous electrolyte solution has been observed in situ by scanning electrochemical microscopy (SECM). SECM was used to image the surface topography of coated metal samples as a function of time in chloride and sulphate solutions. The degradation is observed as a swelling of the polyester coating as a function of time of immersion in chloride solution. The aggressive effect of chloride ions towards coating degradation was established after very short exposure times. No indications of coating failure could be observed by either conventional electrochemical techniques or visual observation. In contrast, blistering could not be observed in a chloride-free sulphate solution. Chloride enhances degradation of the coating at a very early stage.     

Microstructure, microchemistry, and prediction of long-term diffusion behavior of chloride in concrete

Microstructural and microchemical features of two types of concrete are investigated employing electron and ion optical techniques. The first type is the concrete cured in seawater or normal water. The second type is concrete cured in normal water and exposed subsequently to seawater. Major constituent phases of concrete and differences in their distribution due to different curing media are identified. Chloride profiles in different concretes are evaluated using the proton induced x-ray emission technique. Diffusion coefficientD was calculated by modeling the diffusion process and comparing with measured profiles.D, thus estimated, is found to be ∼1.8×10⁻⁹ m²/s, which is higher than the reported values of ∼10⁻¹¹ to 10⁻¹³ m²/s. The faster diffusion of chloride in seawater-cured concrete can be attributed to the availability of water medium in wet concrete, in the initial stages of the hydration of cement. The prediction of the concentration profile of chloride in a layer of 100 mm of 28% fly ash containing concrete over concrete exposed to seawater is carried out. For the worst scenario, analytical estimates of the concentration of chloride as a function of time at a distance of 100 mm in the fly ash containing concrete were made. The concentration profiles of chloride expected after 40 years in the fly ash-containing concrete were also estimated using diffusion coefficient values available in the literature.     

Zum Potentialverhalten der Oberfläche metallischer Werkstoffe bei milder und starker Schwingungskavitation – IV. Aluminium- Werkstoffe

The potential behaviour of the interphase of metallic materials at mild and strong vibratory cavitation IV. Aluminium-base materials In continuation of the reports already published in previous issues of this periodical the authors present results obtained with aluminium base materials, and in particular pure aluminium, AlMg 5, AlZnMgCu 1.5 and AlCuMg 2. The aggressive media used were sodium chloride solutions and artifical sea water. The potential shift is rather small, even under moderate cavitation conditions; only at rather high accélérations (up to 65000 g and more) the potential displacement may exceed ?500 mV. The copper containing alloys form an exception because their potential is constant in the aerated sodium chloride solution in the range of intensities studied. In cases when the protective layer is destroyed and the potential is shifted to more negative values attention has to be paid to the danger of accelerated corrosion in addition to erosion corrosion.