Study on the corrosion behavior of reinforcing steel in cement mortar by electrochemical noise measurements

The corrosion behavior of reinforcing steel in cement mortar has been studied by electrochemical noise (EN) compared with the electrochemical impedance spectroscopy (EIS). The wavelet transform, as well as the statistical methods including the standard deviation of current noise (σ_I) and noise resistance (R_n), has been employed to analyze the EN data of reinforcing steel in mortar. It is revealed that there exist three different corrosion stages of reinforcing steel in cement mortar, including a competition process between breakdown and repassivation of passive film, a pitting development and an active corrosion during the 20 cyclic immersion and drying tests. The energy distribution plot (EDP) is able to provide useful information about the dominant process for the different corrosion stages.     

基于不同胶凝材料钢筋混凝土耐腐蚀性试验研究

针对混凝土结构中钢筋的锈蚀问题,以普通硅酸盐水泥和镁水泥作为胶凝材料,制作了钢筋裸露和涂有环氧树脂涂层的4种钢筋混凝土试件,将其浸泡在氯盐、硫酸盐及镁盐的耦合溶液中,利用电化学方法得到极化曲线和交流阻抗谱,通过塔菲尔外推法进行非线性最小二乘法拟合计算得到腐蚀电流密度、腐蚀电位、腐蚀速率等相关评价指标来衡量混凝土中钢筋锈蚀情况.结果表明:长期浸泡在耦合盐溶液中,普通硅酸盐水泥和镁水泥钢筋混凝土试件都发生了较严重的腐蚀,普通硅酸盐水泥的抗腐蚀性优于镁水泥;在钢筋表面涂有GHT涂层可极大地降低钢筋的腐蚀速率;镁水泥GHT涂层混凝土试件的抗腐蚀性能劣于硅酸盐GHT涂层混凝土试件但优于硅酸盐裸露钢筋混凝土.     

矿物掺合料与钢筋表面状态对砂浆中钢筋锈蚀的影响

通过电化学方法和剖开型观察方法研究了不同矿物掺合料(硅灰和粉煤灰)和不同钢筋表面状态(预钝、预锈和未处理)对砂浆试样中的钢筋锈蚀行为的影响.用电化学阻抗谱法测试钢筋的腐蚀速率和与钢筋锈蚀相关的电化学参数.结果表明:硅灰由于发生火山灰反应而明显降低体系的pH值,且硅灰结合氯离子的能力明显弱于粉煤灰,氯离子临界值也低于掺粉...     

Corrosion mechanisms of steel concrete moulds in the presence of a demoulding agent

The behaviour of E24 mild steel, the constituent steel of most moulds for concrete, was studied by voltamperometry and electrochemical impedance spectroscopy in two electrolytes: (i) a filtered cement solution and (ii) a homogeneous mortar without large air cavities. Experiments were carried out with and without Aquadem^®, a demoulding agent in aqueous phase. In the filtered cement solution, the E24 steel is passivated and the passivation mechanism is totally controlled by the anodic process, not by oxygen reduction. Whatever the experimental conditions (O₂ concentration, rotation speed, immersion time), the corrosion current, i _cor, is equal to the anodic plateau current and is of the order of 0.8 A cm^–2. Therefore i _cor can be directly assessed from the steady state current–potential curves. The E24 steel in contact with a homogeneous mortar without large air cavities is passivated as well as in the filtered cement solution. For both electrolytes, the results are independent of the presence or absence of Aquadem^®. Therefore the pitting corrosion observed in service conditions does not arise from the presence of a solid phase in the electrolyte but may result from the heterogeneity of concrete created by air cavities.     

Diffusion of chloride ions in polymer‐mortar composites

In recent years, the rapid deterioration of various reinforced concrete structures has been a widely recognized problem in the world. Penetration of chloride ions into the concrete structures was found to be the major cause of premature corrosion of reinforcing steel and to promote their deterioration. The present articles deals with the resistance to chloride penetration of polymer‐mortar, which are often used as low‐cost promising materials for preventing or repairing various reinforced concrete structures. To gain more knowledge on the efficiency of polymer‐mortar, four mortar mixtures: one specimen with Portland cement (control sample) and three mixtures with 2.5, 5, and 7.5 wt % of the replacement of cement by polyethylene terephthalate (PET) were tested for chloride ion permeability under immersion in 5% sodium chloride solution. Their chloride ion penetration behavior is discussed by applying Fick's second law. In conclusion, the chloride ion penetration depth and apparent chloride ion diffusion coefficient of the polymer‐mortar composites are smaller than those of unmodified mortar. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Corrosion behaviour of innovative stainless steels in mortar

The main problem of the building sector is the limited durability of reinforcing concrete structures under highly aggressive environments due to the corrosion of reinforcements. In order to demonstrate that stainless steels are the adequate solution to avoid corrosion of reinforced concrete structures by contained chlorides, the corrosion behaviour of AISI 304 and AISI 316L stainless steels in mortar with two chloride doses is compared with the corrosion behaviour of three new stainless steels of low Ni content and reduced cost, and with the traditional carbon steel. The lowest chloride contamination (2% Cl⁻) has been used in this research to provoke corrosion in an active state of reinforcing carbon steel, whereas the highest one (5% Cl⁻) exceeds all expected levels found in the natural environment, including sea water. The new stainless steels remain in the passive state in mortar specimens with both chloride contents.     

Effect of carbon fibres on the mechanical properties and corrosion levels of reinforced portland cement mortars

The changes in mechanical properties of portland cement mortars due to the addition of carbon fibres (CF) to the mix have been studied. Compression and flexural strengths have been determined in relation to the amount of fibres added to the mix, water/binder ratio, curing time and porosity. Additionally, the corrosion level of reinforcing steel bars embedded in portland cement mortars containing CF and silica fume (SF) have also been investigated and reinforcing steel corrosion rates have been determined. As a consequence of the large concentration of oxygen groups in CF surface, a good interaction between the CF and the water of the mortar paste is to be expected. A CF content of 0.5% of cement weight implies an optimum increase in flexural strength and an increase in embedded steel corrosion.     

The performance of a migrating corrosion inhibitor suitable for reinforced concrete

The protection provided by a migrating corrosion inhibitor (MCI) based on an alkylaminoalcohol was tested on concrete specimens containing reinforcing steel bar (rebar) segments. Two inhibitor dosages were investigated, together with two water/cement ratios and various chloride contents. The inhibition efficiency was followed over a period of 1000 days measuring electrical and electrochemical parameters such as the corrosion potential, the corrosion current density, the electrical resistance and performing electrochemical impedance spectra. The inhibitor was able to reduce the corrosion rate only when the initial chloride content was below 0.16 wt.% (percent weight relative to cement content). The efficiency increased as the water/cement ratio increased. There was no beneficial effect when the initial chloride content was greater than 0.43 wt.%. The efficiency of the product increased when the amount of inhibitor being applied doubled.     

Effect of steel microfibers on corrosion of steel reinforcing bars

Steel microfiber reinforcement was previously found to be successful in mitigating alkali silica reaction in concrete, an expansive phenomenon. The use of steel microfibers to mitigate rebar corrosion, another expansive reaction, was investigated. Mortar specimens with and without steel microfiber reinforcement were exposed to a corrosive environment. All specimens were prepared with water/cement ratios of both 0.40 and 0.55, cured for 28 days, and then submerged in aerated 3.5% NaCl solution. The corrosion behavior of the specimens was monitored via electrochemical measurements. Three types of electrochemical tests were performed: corrosion potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Chloride concentration measurements and microscopic analysis were performed as well. The polarization curves, Tafel, and polarization resistance measurements indicate that the steel rebar in the microfiber-reinforced mortars are more resistant to corrosion than the rebar in the control mortars, despite higher chloride concentrations. Furthermore, the steel microfiber-reinforced cement based materials have a lower electrolytic resistance. This is not indicative of a higher corrosion rate, which would be the case if it had been observed in standard mortar specimens.     

Limitations and advantages of electrochemical chloride removal in corroded reinforced concrete structures

Existing experience on electrochemical methods for the rehabilitation of corroded reinforced concrete structures (RCS) shows that chlorides can be removed from these structures and that carbonated concrete can be realkalised. However, the current state of know-how has not advanced sufficiently to dissipate serious doubts about the efficiency of electrochemical chloride removal (ECR) and electrochemical realkalisation (ERA). A fundamental controversy remains to be resolved, which can be summarised in the following question: Once the causes of corrosion have been removed, does the corrosion of corroded RCS cease?The present work attempts to find an experimental response to this question, determining the corrosion rates of corroded rebars embedded in cement mortar slabs with chloride additions, before and after the application of ECR, and of clean and prerusted steel electrodes embedded in small chloride-free mortar specimens. According to the results obtained, if ECR is applied preventively it is an efficient procedure for delaying the start of corrosion. However, if applied too late it does not assure the repassivation of corroded RCS and is therefore useless.     

Spatial distribution of crystalline corrosion products formed during corrosion of stainless steel in concrete

The mineralogy and spatial distribution of nano-crystalline corrosion products that form in the steel/concrete interface were characterized using synchrotron X-ray micro-diffraction (μ-XRD). Two types of low-nickel high-chromium reinforcing steels embedded into mortar and exposed to NaCl solution were investigated. Corrosion in the samples was confirmed by electrochemical impedance spectroscopy (EIS). μ-XRD revealed that goethite (α-FeOOH) and akaganeite (β-FeOOH) are the main iron oxide–hydroxides formed during the chloride-induced corrosion of stainless steel in concrete. Goethite is formed closer to the surface of the steel due to the presence of chromium in the steel, while akaganeite is formed further away from the surface due to the presence of chloride ions. Detailed microstructural analysis is shown and discussed on one sample of each type of steel.     

Development of a galvanic sensor system for detecting the corrosion damage of the steel embedded in concrete structure: Part 2. Laboratory electrochemical testing of sensors in concrete

The correlation between sensor output and the corrosion rate of steel bar was confirmed in concrete environment. Open-circuit potential, linear polarization resistance (LPR) measurement and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of steel bar embedded in concrete. Also, galvanic current measurements of designed sensors were conducted to obtain the charge of sensor embedded in concrete.In this study, the results of corrosion behavior of reinforcing steel showed a consistence among the data obtained by open-circuit potential monitoring, LPR and EIS measurements. Steel/copper sensor showed a good correlation in concrete environment between sensor output and corrosion rate of steel bar. However, there was no relationship between steel/stainless steel sensor output and corrosion rate of steel bar due to the low galvanic current output. Through the relationship between the steel/copper sensor output and the corrosion rate of reinforcing steel, the real corrosion damage of the reinforcing steel can be detected. Consequently, this confirms that the galvanic sensor system is a good method for detection of corrosion in reinforced concrete.     

The use of migrating corrosion inhibitors to repair motorways' concrete structures contaminated by chlorides

The effectiveness of migrating corrosion inhibitors (MCIs) and repair mortars against rebar corrosion was studied in concrete specimens made by ordinary Portland cement with w/c ratio equal to 0.6 and containing 1 wt.% of chlorides. An alkanolamine-based inhibitor was tested in addition with a common mortar and two repair mortars. Electrochemical techniques, measurements of corrosion potential and electrochemical impedance spectroscopy (EIS) were used to determine the corrosion behaviour of the specimens when a cell containing a 3.5% NaCl solution was applied on the rehabilitation mortar. Mercury intrusion porosimetry (MIP) was also used for the characterisation of repair mortars' total porosity and a chemical analysis was made to determine the amount of chlorides penetrated in the mortar layers and in the concrete substrate. Results demonstrate that the simultaneous use of the alkanolamine-based inhibitor with a good barrier coating offers protection against rebar corrosion and allows rehabilitation of deteriorated concrete structures.     

阻锈剂对海水拌和再生胶砂力学性能和钢筋腐蚀行为的影响研究

针对海水拌和再生骨料混凝土的耐久性问题,对比分析了两种阻锈剂在单掺和复掺下对海水拌和再生胶砂力学性能和钢筋腐蚀行为的影响,并通过X射线衍射(XRD)、压汞(MIP)等测试手段分析其影响机理。结果表明:海水拌和再生胶砂在不掺阻锈剂的情况下前期腐蚀速度较快,7 d后腐蚀速度较慢,逐渐趋于钝化;氨甲基丙醇对海水拌和再生胶砂力学性能和钢筋锈蚀性能起不利影响,主要原因是其抑制了水泥水化进程,增加了孔隙数量;五水偏硅酸钠能使海水拌和再生胶砂中的钢筋发生钝化,具有显著阻锈作用,同时可促进C-S-H的形成,优化孔结构,对海水拌和再生胶砂力学性能影响较小。该试验可对海水拌合再生骨料混凝土耐久性的改善和服役安全性的提升提供参考。     

Corrosion resistance in activated fly ash mortars

The question of whether reinforcing steel can be protected with activated fly ash cement as effectively as with Portland cement is explored in this study. Corrosion potential (E_corr) and polarisation resistance (R_p) values for steel electrodes embedded in Portland cement mortar and two fly ash mortars, respectively activated with NaOH and waterglass+NaOH solutions, are monitored. Chloride-free activated fly ash mortars are found to passivate steel reinforcement as speedily and effectively as Portland cement mortars, giving no cause to fear that corrosion may limit the durability of reinforced concrete structures built with these new types of activated fly ash cement. The polarisation curves and the response to short-term anodic current pulses (galvanostatic pulse technique) obtained further corroborate the full and stable passivation of the steel by the concrete manufactured with these binders.     

Application of gamma-ray radiography and gravimetric measurements after accelerated corrosion tests of steel embedded in mortar

The accelerated corrosion by the impressed current technique is widely used in studies of concrete durability since it has the advantage that tests can be carried out within reasonable periods of time. In the present work the relationship between the applied current density and the resulting damage on the reinforcing steel, by applying optical microscopy, scanning electron microscopy, gamma-ray radiography and gravimetric measurements, was studied by means of the implementation of accelerated corrosion tests on reinforced mortar. The results show that the efficiency of the applied current is between 1 and 77%, regardless of the applied current density, the water/cement ratio and the mortar cover depth of the specimens. The results show the applicability of the gamma-ray radiography technique to detect localized corrosion of steel rebars in laboratory specimens.     

玻璃钢筋混凝土的有限元计算与试验

钢筋混凝土广泛应用于土木工程领域，但其结构耐久性因钢筋本身的锈蚀成为现今急待解决的问题。人们一直在寻找对钢筋混凝土进行改良的途径，用玻璃钢筋代替普通钢筋是解决这一问题的一个有效的方法，为此进行了试验和ANSYS有限元分析，结果证明此法具有可行性。     

Voltammetric behaviour of iron in cement. III. Comparison of iron versus reinforcing steel

The cyclic voltammetric behaviour of reinforcing steel in cured Portland cement paste was investigated and compared with that of pure iron. The cyclic volammetric behaviour of reinforcing steel in cement is very similar to that reported earlier for iron in cement, both with and without NaCl and NaNO₂ (a corrosion inhibitor) additions. This similarity confirms that the results and conclusions obtained using iron are also applicable to the behaviour of reinforcing steel. A useful method for determining true surface areas of iron or steel electrodes by linear sweep voltammetry also is described in detail.     

Effect of cement type on the corrosion of reinforcing steel bars exposed to acidic media using electrochemical techniques

The effect of different percentages of cement components (tricalcium aluminate C₃A) on the corrosion of embedded reinforcing steel bars was studied in presence of 5% NaCl or 5% MgSO₄ solutions. Different electrochemical techniques namely; half-cell potential measurement, impressed voltage method and impressed current method were used. The C₃A in cement reduced greatly the corrosion of steel bars embedded in concrete subjected to chloride or sulphate solutions. In chloride solution, as the percent of C₃A increased in cement from 2% to 10% the steel corrosion decreased proportionally. The rate of corrosion in 5% MgSO₄ solution was decreased as the percent of C₃A increased from 2% to 6%. From 6% to 10% the steel corrosion rate was rapidly accelerated. In general the presence of chloride and sulphate solutions in surrounding media reduced the destructive effect of sulphate ions on embedded steel bars.