Untersuchung über die Auswirkung der Elementbildung zwischen Stahl in Beton und Stahl in Erdboden

Investigation of the effect of galvanic corrosion between steel in concrete and steel in soil The investigation of cathodic polarization of steel in concrete on samples of portland cement and blast furnace cement revealed that oxygen reduction on steel in portland cement is less hindered than on steel in blast furnace cement. As to the magnitude of the cathodic current the aeration of the samples is important. Dry stored samples before measuring case a higher current density than wet stored ones. A significant relationship of the cathodic current depending on the water/cement value and the storage time of concrete could not be ascertained. The polarization resistances for portland cement samples lie within 86 and 3000 kΩ · cm² and for blast furnace cement samples between 430 and 5100 kΩ · cm². The measurements of the anodic current densities on corrosion cells of steel in concrete/steel in solution and steel in wet sand respectively rendered, by varying the cathode/anode aspect ratio from 1000: 1 to 1: 1, values for portland cement samples between 560 and 1,2 μAJcm² (corresponding to an annual corrosion of 6,5 and 0,014 mm respectively), and for blast furnace cement samples values between 730 and 0,28 μA/cm² (corresponding to an annual corrosion rate of 8,5 and 0,003 mm respectively). A decrease of the anodic current density variable with time could not be observed during the 28 days of measurements. On account of the investigations the following conclusions can be made: A formation of a corrosion cell with steel in concrete/steel in soil is particularly then to be expected if the concrete is dry on one side, e.g. the foundation of a building where oxygen diffuses by way of the gas pores in the concrete from the inner side to the cathode. This is less serious if the concrete is fully embedded in soil and thoroughly moistened. In this case the transport of oxygen has to be carried via waterfilled pores.     

Anodic polarisation measurements of corrosion and corrosion inhibition of Steel in concrete

Abstract

Anodic polarisation experiments were carried out on steel in concrete. The effects of surface treatment of the steel, medium of curing, as well as durations of curing were investigated.

Corrosion of steel in concrete due to the presence of the corroding chloride ions, either added to the mixing water or diffusing from the external attacking medium, was also investigated. The chloride ions when present in the mixing water are more effective in destroying the passivation of steel than when present in the outside medium. In the former case a minimum concentration of 1 % is required for this action, while in the latter case 4% is required.

Anodic corrosion inhibitors like nitrite, chromate, phosphate, benzoate and silicate were tried in order to suppress the action of the corrodent. The minimum concentration required of the inhibitor to stifle the corrosion is generally lower in the case when it is added to the mixing water of concrete. Possible mechanisms of corrosion and corrosion inhibition are discussed in the light of the current views on both processes.     

矿物掺合料对钢筋氯盐腐蚀行为的影响及其作用机理

用水泥提取液模拟混凝土孔隙液,用自腐蚀电位、动电位极化和电化学阻抗技术,研究单掺粉煤灰或矿粉、复掺粉煤灰和矿粉对混凝土中钢筋氯盐腐蚀行为的影响.结果表明,粉煤灰和矿粉均能有效降低钢筋受氯离子腐蚀的风险,减小腐蚀速率,并能不同程度地提高钢筋腐蚀的临界氯离子浓度.抑制氯离子腐蚀能力由强到弱依次为:矿粉>矿粉+粉煤灰>粉煤灰>水泥.且随氯离子浓度的增大,矿粉和粉煤灰的阻锈效率会有不同程度的下降.用矿粉和粉煤灰按适当比例复掺的方法来对抗氯离子腐蚀不仅经济,而且有不错的阻锈效果.     

Corrosion behavior of reinforced no-fines concrete

The CO₂ induced corrosion behavior of no-fines concrete manufactured with three different strength classes and reinforcements is compared. The main results showed that black steel corrodes with rates three times higher with respect to those monitored in the other reinforcements, with higher corrosion rates in lower strength class concretes. The corrosion rates of steel covered by cement grout and galvanized reinforcements are not affected by concrete strength class since they protect themselves with the cement grout coating or zinc passivation, respectively. Among the reinforcements considered in this work, galvanized steel shows the best corrosion behavior.     

Corrosion inhibitors in reinforced concrete structures Part 3 – migration of inhibitors into concrete

Abstract

To prevent and control rebar corrosion in concrete, corrosion inhibitors may be used both as a preventative technique if added to fresh concrete and as a repair system if applied to hardened concrete. In the past six years, an experimental research was performed on both mixed and migrating inhibitors. Effectiveness of mixed inhibitors has been investigated in Part 1: the ability to delay time to corrosion and to reduce corrosion rate has been studied both in the case of chloride-induced corrosion and carbonated concrete. Organic migrating inhibitors were applied to concrete specimens, and their ability to control corrosion was investigated: results are described in Part 2. Results allow to state that the inhibitors are able to delay time to corrosion, while a negligible effect was observed in the reduction of corrosion rate. In the third part, the inhibitor migration into concrete has been analysed in order to quantify inhibitor penetration depth and main penetration mechanism.     

Corrosion and Corrosion Inhibition of Reinforcing Steel: I. Immersed in Alkaline Solutions

Abstract

The electrochemical behaviour of reinforcing steel in stagnant alkaline solutions, especially calcium hydroxide, has been investigated. It was found that the oxidation processes that take place on steel are determined by the degree of surface oxidation of the sample and by dissolved oxygen, but not by the type of cation present.

In aerated solution, ferrosoferric oxide (Fe₃O₄) is the intermediate oxidation product on the steel surface while ferrous hydroxide is the intermediate product in de-aerated solution.

In pure alkaline solutions, the critical pH above which stable passivity occurs is 11·5. This value increases when the alkaline solution is contaminated with aggressive ions or when reinforcing steel having mill-scale on its surface is used. A linear relationship holds between the pH of the alkaline solution and the highest concentration of sodium chloride that can be tolerated (CC1-): pH = n logCcc^? + K where nand K are constants.

Calcium hydroxide solutions prepared fronl water of different local sources act differently towards steel. Thus, in saturated calcium hydroxide solution prepared from either distilled or tap water, the steel becomes passive. In the corresponding solution in mineral or sea water, the metal corrodes. On the other hand, mineral water becomes inhibitive when the pH is increased to 13. Sea water could not be tolerated by mere increase in pH.     

Korrosionsverhalten von unlegierten Stählen bei Berührung mit Baustoffen

Corrosion of unalloyed steels in contact with building materials Embedded in concrete no corrosion of steel occurs even in the presence of water as long as the water in the concrete pores is alkaline enough to maintain the passivity of iron. The passivity can be destroyed by chloride-ions, which may be components of concrete additives. Another possible reason for loss of passivity is the decrease of alkalinity due to the reaction with carbon dioxide. In contact with non alkaline building materials as e.g. insulating material corrosion is guided mainly by the access of water. A very high risk of corrosion damage occurs due to a galvanic element when steel in contact with non alkaline material is connected by metallic and electrolytic conductor with steel in concrete.     

钢渣矿渣水泥性能的研究

以钢渣、矿渣、水泥熟料为主要原料,并掺入少量激发剂,成功制备了高强、高钢渣掺量的钢渣水泥。探讨了激发剂、熟料掺量、钢渣掺量对钢渣水泥性能的影响。并通过SEM、XRD分析了激发剂对钢渣水泥水化产物及水泥石微观结构的影响。结果表明:激发剂显著提高了钢(矿)渣的活性,从而大幅度提高了钢渣水泥的早期性能。掺加激发剂后,钢渣水泥3d抗压强度可增加119.7%,激发剂对水泥水化产物的种类影响不大。与硅酸盐水泥相比,钢渣水泥浆体中C-S-H凝胶和AFt晶体含量明显增多,Ca(OH)2晶体含量显著降低。     

Chloride threshold for rebar corrosion in concrete with addition of silica fume

The effect of silica fume on the chloride threshold for the initiation of pitting corrosion of steel in concrete was investigated. Laboratory tests were carried out in concrete specimens made with ordinary Portland cement and with 10% of silica fume. Chloride contents up to 2% by mass of cement were added to the mixes, in order to investigate the corrosion rate of embedded bars made of both strengthened and mild steel. A lower chloride threshold was observed in the bars which were embedded in concrete with silica fume compared to those embedded in concrete made of Portland cement.     

Accelerated Corrosion of Metallic and Reinforced Concrete Constructions when Connected to Lightning Conductors

Abstract

With the object of examining the influence on the corrosion of metallic and reinforced concrete constructions of their connection to lightning conductors (as is demanded by the regulations of some countries), the following measurements were made: (1) corrosion potentials of steel and copper specimens (in the form of sheets) in distilled water at 25°c vs time: (2) potentiostatic curves of steel and copper specimens (in the form of sheets) in distilled water at 25° c; (3) weight loss of steel and copper specimens in the form of sheets (in ASTM corrosion chamber) and in the form of tubes (by internal circulation of artificial sea water at 70° c) and of the reinforcements of reinforced concrete specimens (in circulating sea water at 25°c). All these experiments were done with the specimens both unconnected and connected to lightning conductors (or needles); in some cases artificial lightning was introduced. These experiments proved that connecting metallic specimens and reinforcements of reinforced concrete to lightning conductors (or metallic needles) increased their corrosion rate.

In subsequent papers the results of pilot plant and full scale experiments under natural conditons will be presented.     

Determination of Corrosion and Inhibition of Mild Steel in HNO3 by the Thermometric (Mylius) Technique

Abstract

The thermometric (Mylius) technique has been found to be suitable for determining the action of nitric acid on steel and the effectiveness of inhibitors. This technique may be usefully applied in controlling pickling and acid-cleaning baths by determining the threshold concentrations of inhibitors and checking their depletion during service.

The increase in the rate of attack on steel by HNO₃ with increase in concentration is shown by both weight-loss measurements and the value of the reaction number (R.N.) derived from the thermometric measurements. In HNO₃ at concentrations producing passivity no temperature rise occurs. Lower RN values and, accordingly, lower corrosion rates are obtained in the presence of thiourea, KI, NaCl, and HCl. The presence of an accelerator (NaNO₂) produces higher RN values. Thiourea is able to arrest corrosion occurring in uninhibited HNO₃. Progressive additions of an inhibitor and the recording of the accompanying temperature rise enable the threshold concentration of an inhibitor to be determined.     

The influence of cracks on chloride-induced corrosion of steel in ordinary Portland cement and high performance concretes subjected to different loading conditions

Many reinforced concrete structures are subjected to variable loads, but little information is available on the effect of such loading, and the accompanying opening and closing of cracks, on the initiation and propagation of chloride-induced rebar corrosion. The purpose of this paper is to provide that information for reinforced ordinary Portland cement concrete and high performance concrete exposed to static or cyclic three-point bending and exposed to salt solution.It was observed that: (i) corrosion occurred only at intersections of the rebar with cracks in the concrete; (ii) high performance concrete was more protective than ordinary Portland cement concrete and (iii) the type of loading had less impact on corrosion than the type of concrete and exposure conditions.     

Corrosion of Reinforcing Bars in Carbonated Concrete

Abstract

In all published studies of cement carbonation there has been general agreement that it must be considered as a cause of generalised corrosion in reinforcements, but quantitative data have been provided in very few cases. In the present work the intensity of attack has been modified by means of the accelerated carbonation of mortar specimens without additives, with 2% CaCl², and with 3% NaNO² It has been shown that a critical level of atmospheric moisture must also be present for considerable attack to occur. The measurement of polarisation resistance (Rp) has been used to evaluate the intensity of corrosion of the reinforcements. This method has already been usefully applied by the authors to investigations of corrosion of steel bars in hardened concrete specimens.     

Ternary mixes with high mineral additions contents and corrosion related properties

The choice of blended cements and materials with cementitious properties in concrete is currently seen as a choice that increases the environmental sustainability of the construction industry. The developments with non‐traditional binders (such as the simultaneous incorporation of several types of supplementary cementitious materials) have highlighted new challenges to be researched. In the present paper ternary binders were prepared by mixing ordinary Portland cement (OPC) plus two blended components: low calcium fly ash, blast furnace slag, and/or limestone filler. Several physical and mechanical properties of ternary blend systems have been analyzed in mortar form at several curing ages: 2, 7, 28, and 90 days. Additionally preliminary tests of corrosion performance of reinforcement in these types of mixes have been considered. The results indicate that the use of appropriate content components in ternary blends will allow binders to fulfill the specified mechanical requirements. The best results are obtained when two additions with antagonist properties are mixed, as fly ashes and slags or slags and filler limestone. Besides, certain influence of the effect on durability performance is detected, in particular associated with the stability of the passive state and corrosion of reinforcements in presence of chlorides.     

Industral News

Abstract

The validity of the ac impedance technique has been tested using polished steel samples cast in concrete cubes, followed by immersion in oxygen-saturated sea water and distilled water. In order to accelerate the corrosion processes the concrete used was very porous with a low cover thickness and comparisons were made with samples of pre-rusted steel specimens.

The impedance results show that, as well as estimating the corrosion rates, information related to the surface film on the steel may also be obtained. The data are in accord with corrosion potential measurements; The results highlight a problem inherent in dc polarisation techniques when applied to the study of corrosion of reinforcing steel in concrete, namely, that steady state data are only obtained many hours after the initial measuring perturbation.     

Effect of surface condition on the initial corrosion of galvanized reinforcing steel embedded in concrete

The present work was aimed at determining the effect of coating surface condition on the initial corrosion of hot-dip galvanized reinforcing steel bar (HDG rebar) in ordinary Portland cement (OPC) concrete. During zinc corrosion in OPC concrete, calcium hydroxyzincate (CHZ) formed on untreated HDG steel provided sufficient protection against corrosion. Therefore, it is concluded that treating HDG rebar with dilute chromic acid is unnecessary as a method of passivating zinc. A layer of zinc oxide and zinc carbonate formed, through weathering, on HDG bars increased the initial corrosion rate and passivation time compared with the non-weathered rebar exposed to concrete. HDG steel with an alloyed coating, i.e. containing only of Fe-Zn intermetallic phases, required a longer time to passivate than those with a pure zinc surface layer. The lower zinc content of the surface limited the rate of CHZ formation; hence, delayed passivation. Regardless of the surface condition, the coating depth loss after two days of embedment in ordinary Portland cement concrete was insignificant.     

Einfluß einer Feuerverzinkung und PVC-Beschichtung von Bewehrungsstählen und von Inhibitoren auf die Korrosion von Stahl in gerissenem Beton

Influence of galvanizing and PVC-coating of reinforcing steels and of inhibitors on steel corrosion in cracked concrete Cracked concrete beams of concrete quality B15 and B35 with carbonized cracks were exposed in artificial seawater, under frost and deicing salt conditions and in industrial climate. The reinforcement was composed of black steel, galvanized and PVC-coated steel. For the purpose of additional protection the concrete was partly mixed with an inhibitor Ca(NO₂)₂. The concrete cover was 1,5 till 5,0 cm. It was found that the inhibitor protects satisfactorily only in the case of the higher concrete quality, cover 1,5 cm and not to high crack width. A protective effect of galvanizing is given by not to high chloride contents (< 1,5% relative to cement) and crack widths. The chosen PVC-coating failed because of chemical instability in the alcaline medium concrete.     

Chloride-induced steel corrosion in alkali-activated fly ash mortar: Increased propensity for corrosion initiation at defects

Chloride contents at the steel–mortar interface that initiate steel corrosion were determined for carbon steel in alkali-activated fly ash mortar for three different exposure conditions: exposure to 1 M NaCl solution; leaching in deionized water and then exposure to 1 M NaCl solution; and leaching in deionized water, aging in air at 20°C and natural CO₂ concentration, and then exposure to 1 M NaCl solution. For comparison, a Portland cement mortar, exposed to 1 M NaCl solution, was studied. The median values of the corrosion-initiating chloride contents (average over the full length of the rebar) in the alkali-activated fly ash mortar varied between 0.35 and 1.05 wt% Cl with respect to binder, consistently lower than what was obtained for the Portland cement mortar, but with no clear trend regarding the exposure conditions. For most of the alkali-activated fly ash mortar specimens, preferential corrosion at the connection between the working electrode and the external measurement setup was observed, while preferential corrosion did not occur for the Portland cement mortar. Scanning electron microscopy and auxiliary experiments in synthetic solutions indicated that this behavior was caused by inhomogeneities at the steel–mortar interface in the alkali-activated mortar, likely due to its peculiar rheological properties in the fresh state.     

Corrosion testing on steel reinforced XD3 concrete samples prepared with a green inhibitor and two different superplasticizers

In recent years, the use of corrosion inhibitors in producing high‐performance steel reinforced concrete structures has increased significantly to minimize the chloride and sulfate attacks. However, most inhibitors available in the market are toxic to the environment. Hence, one objective of the present investigation was to test a novel, eco‐friendly, so‐called green inhibitor extracted from a fruit waste (orange peel), and its effects were studied on the compression strength of the XD3 type concrete samples. The inhibitor was added to the concrete mix in concentrations of 1% and 3% by weight of cement in addition to two different superplasticizers (Mapei Dynamon SR 31, Budapest, Hungary and Oxydtron, Hungary). The test results on steel reinforced samples immersed in 3.5 wt% NaCl aqueous solutions at room temperature showed promising corrosion mitigating effects just after 6 months testing period. The lower corrosion currents (i.e., better corrosion resistance) after 6 months immersion were observed when the samples contained both green inhibitor and Oxydtron superplasticizer, especially with sample C2 (in this case 3% green inhibitor was added to the mixture of cement + Oxydtron superplasticizer).     

Corrosion of steel reinforcement in structural concrete with carbon material addition

Different types of carbonaceous materials have been added to concrete mixes and their effect on the corrosion of embedded steel has been studied. Using a constant water/cement ratio of 0.42 and different amounts of carbonaceous materials and different curing periods the evolution of the corrosion process in the embedded reinforced bars has been determined. The addition of small quantities of carbonaceous materials to the mixture produces a reduction of the concrete permeability. Tests demonstrate that a decrease of the corrosion level occurs when the content ratio of carbon material addition is increased.