混凝土中钢腐蚀的有关问题毕业论文外文翻译

1、外文翻译some questions on the corrosion of steel in concrete.corrosion mechanism and monitoring, servicelife prediction and protection methods abstract：this second part addresses some important issues that remain controversial despite the vast amounts of work devoted to investigating corrosion in concre

2、te-embedded steel. specifically,these refer to: 1) the relative significance of galvanic macrocouples and corrosion microcells in reinforced concrete structures; 2) the mechanism by which reinforcements corrode in an active state; 3) the best protective methods for preventing or stopping reinforceme

3、nt corrosion; 4) the possibility of a reliable prediction of the service life of a reinforced concrete structure ; and 5) the best corrosion measurement and control methods. the responses provided are supported by experimental results, most of which were obtained by the authors themselves. 1. introd

4、uctionconcrete-embedded steel is known to remain in apassive state under normal conditions as a result of the highly alkaline ph of concrete. the passivity of reinforcements ensures unlimited durability of reinforced concrete (1kc) structures. however, there are some exceptional conditions that disr

5、upt steel passivity and cause reinforcements to be corroded in an active state. this has raised controversial interpretations, some of which were discussed in part i of this series 1. this part ii analyses though far from exhaustively, other - to the authors minds at least - equally interesting issu

6、es on which no general consensus has been reached.2. materials and methodsthe reader is referred to part i for a detailed description of the materials and methods used in this work. most of the experimental results discussed herein were obtained with the same types of specimens and slabs.galvanic co

7、uples were determined on speciallydesigned specimens, such as those shown in figs. 1 and 2.near-real conditions were simulated by using a beam that was 160cm long and 7 x 10 cm in cross-section. the beam was made from 350 kg cement/m 3, half of whichcontained no additives, while the other half inclu

8、ded 3% cac12 by cement weight 2, (fig. 1). in order to study the effect of the sanod/scathoa ratio on galvanic macrocouples, they were modelled by surrounding a small carbon steel anode with a stainless steel (aisi 304) cathode and vice versa(fig. 2). in this way, the ratios consistensy was assured.

9、 in addition, the potential and icorr of stainless steal and those of the passive structures were very similar. fig. 1 - beam used to measure icotr and ecorr in fig. 2 - scheme of galvanic macrocouples embedded concrete with and without chlorides and to in chloride- containing mortar used to study t

10、heillustrate the significance of passive steel/active effect of the sanod/scathod ratio and their relativesteel macrocouples. significance to corrosion microcells.3. results and discussion3.1 what is the relative significance of galvanic macrocouples and corrosionmicrocells in rc structures ?accordi

11、ng to several authors 3, 5, the polarization resistance method provides an effective means for estimating the corrosion rate of steel in p,c ; the method is quite rapid, convenient, non-destructive, quantitative and reasonably precise. however, it is uncertain whether it may give rise to serious err

12、ors with highly-polarized electrodes by the effect of passive/active area galvanicmacrocouples in the reinforcements 6.based on the authors own experience with the behaviour of galvanic macrocouples in pc, the contribution of these macrocouples to overall corrosion is very modest rehtive to that of

13、the corrosion microcells formed in the active areas of reinforcements in the presence of sufficient oxygen and moisture 2, 7, 8. thus, it has been experimentally checked that:(a) galvanic macrocouples have a slight polarizing effect on anodic areas in wet concrete, whose potential is thereby influen

14、ced in only a few millivolts.(b) on the other hand, macrocouples have a strong polarizing effect on passive areas despite the low galvanic currents involved relative to the overall corrosion current.(c) as a result, galvanic currents can result in grossly underestimated icorr values for the active a

15、reas since they are often smaller than 10% of the ico= values estimated from polarization resistance measurements.(d) the corrosive effect ofcoplanar macrocouples on rc structures only proves dangerous within a small distance from the boundary of active and passive areas.fig. 3 compares the estimate

16、d icorr and ig values, in mortar containing 3 o a cac12, per anode surface unit for a number of anode/cathode surface ratios for aisi 304 stainless steel/carbon steel macrocouples in support of the above conclusions 9.3.2 by what mechanism do reinforcements corrode in an active state ?when the passi

17、ve state is lost, the rate of reinforcement corrosion in inversely proportional to the resistivity of concrete over a wide resistivity range 10. because fig. 3 - relative significance of corrosion microcells fig. 4 - trends in ico. and ecorr for (icorr) and galvanic macrocouples (i.) in corrosion sp

18、ecimens exposed to an oxygen-free of steel embedded in mortar containing no chloride. environment.both currents were calculated relative to sanod (carbon steel in the macrocouples of fig. 2).the environments relative humidity and ionic additives of concrete determine concrete resistivity, these fact

19、ors, together with oxygen availability at reinforcement surfaces,control the corrosion rate 11.the electric resistivity of water-saturated concrete structures is relatively very low, and the corrosion rate is believed to be essentially controlled by the diffusion of dissolved oxygen through the conc

20、rete cover up to reinforcements. this is consistent with the widespread belief that the sole possible cathodic reaction in neutral and alkaline solutions is oxygen reduction.the significance ascribed to the role of oxygen justifies the efforts to determine its diffusion coefficient in concrete12, 13

21、. the variety of methods and experimental conditions used for this purpose have led to a wide range of diffusivity values (from 10 -12 to 10 -8 m2/s) for oxygen incement paste 14.since the diffusion coefficient of oxygen in aqueous solutions (1)o2 = 10 -5 cm2/s-1), is saturation concentration (co2 =

22、 2.1 x 10 -7 mol/cm 3) and the approximate thickness of diffusion layers in stagnant solutions (8 = 0.01 cm) are wellknown, the limiting diffusion current can be calculated as :ilo2 = - z fd02c02/r = 8 x 10 -4 a/cm 2 (80 pa/cm 2)where z is the number of equivalents per mole (4) and f the faraday (96

23、,500 a.s/eq).for 1-cm thick mortar covers of average porosity 15%(see fig. 1 in part i) 1 and a diffusioja layer thickness of the same order as the cover thickness, 11o2 = 0.12 laa/cm 2, which is quite consistent with the icorr values estimated under pore saturation conditions at the end of the curi

24、ngprocess, both for mortars containing no chloride ions and for those including 2, 4 or 6% c1- 16.on the other hand, icorr values of ca. 10 lia/cm 2 (see fig. 9 in part i) 4 have been obtained by several authors for mortars with chlorides or carbonated mortars which are incompatible with the rates a

25、llowed by the limiting diffusion current of oxygen. therefore, in some circumstances, alternative cathodic processes allowing for faster kinetics must therefore be involved. in recent work, the concurrence of crevices, chloride ions and dissolved oxygen at the steel/concrete interface was claimed to

26、 provide the thermodynamic conditions required for protons to be reduced and the alternative mechanism to occur 11, 17.there are a number of facts that refute oxygen reduction as being the sole corrosion rate-determining step, namely: - under some circumstances, once corrosion in an activestate has

27、started, it develops at the same rate even though oxygen is being removed from the medium (fig. 4) 11.- as saturation of concrete pores decrease, concrete resistivity controls icor over a wide resistivity range ; therefore, the corrosion rate seems to decrease in proportion to the ease with which ox

28、ygen penetrates into the structure(fig. 5)10.on the other hand, there are several arguments in favour of proton reduction in ca(oh)2-saturated solutions or cement mortars 11 :- the ph decreases from 12.6 to ca. 5 within crevices at the steel/electrolyte interface upon exposure of the steel to a ca(o

29、h)2-saturated solution with c1- additions and wellaerated. if sufficient oxygen is available, the ph can drop as low as 1-2.- the emergence of acid exudates ofph 1-5 from cracks and macropores in chloride-containing mortar specimens under wet atmospheres at high corrosion rates (5-10 pa/cm2).- the f

30、ormation of gas bubbles over iron hydroxide membrane-coated pits when the steal is polarized anodically in a ca(oh)2-saturated, chloride-contaminated solution at potentials below those required for oxygen release. everything points to pits with a low enough ph for the anodic current applied to overl

31、ap with a corrosion process involving proton reduction as a cathodic half-reaction.when concrete-embedded steel is corroded in an active state, its corrosion kinetics rise exponentially with increasing pore saturation (fig. 6), similarly to atmospheric corrosion in bare steel as the environments rel

32、ative humidity increases 18. at some points in the reinfor- cements, a catalytic cycle may take place, e.g., those put forward by schikorr for atmospheric corrosion of steel 19, with chloride ion rather than so2-as the catalyst (fig. 6). fig. 5 - relationship between mortar resistivity fig. 6 - infl

33、uence of the degree of pore saturation and the corrosion rate of reinforcements. on the corrosion rate of reinforcements.中文翻译混凝土中钢腐蚀的有关问题腐蚀机理和监督、使用年限的预测和保护方法 摘要:第二部分阐述几个仍然存在争议的重要问题，尽管已经在混凝土中钢腐蚀的调查研究投入了大量的工作。特别是这几方面：1)在钢筋混凝土结构中的大电偶和腐蚀微电池对的相对重要性；2)激活状态的钢筋腐蚀机理；3)阻止或停止钢筋腐蚀最好的保护方法；4)一个钢筋混凝土结构使用年限的可靠预测的可能

34、性探索；5)最好的防腐措施和控制方法。这些回答需要试验得出，大部分都由作者们得出。1.前言正常条件下强碱混凝土中的钢仍然处于钝化状态。钢筋的钝性能保证钢筋混凝土结构无限的耐久性。然而，有一些能破坏钢的钝性和引起钢筋腐蚀的实验条件。在第部分中讨论到的一些实验结构已经引起了很多争论1。第部分的分析虽然没有竭尽全力，但至少是作者的意思，就像有趣的问题有不同的意见一样。2.材料和方法读者指出在第部分详细描述了用于这项工作的材料和方法。这里所讨论的大部分实验结果都是从一样的试块和平板中得到的。电偶是由特殊设计的试块确定的，如图1和2所示。用一根长16m，70mm100 mm横截面的梁模拟近真实条件。梁是

35、由每立方米350kg水泥制成，梁的一半含有添加剂，另一半含有水泥的重量的3%的cacl22，(图1)。为了了解s正极/s负极的比值对大电偶的影响，用在一个小的碳素钢正极环绕一个不锈钢负极并夹紧来模拟。这样，比值的连贯性是可靠的。此外，与钝化结果的电位和不锈钢的icorr是非常相似的。 图1.梁用来分别测量混凝土中含有和不含有氯化物 图2.用电耦合牢牢嵌入含有氯化物的砂浆里来研究的icorr和ecorr来说明钝化钢/活跃钢耦合的意义。 s正极/s负极的作用和腐蚀微电池对的相对意义的方案。3.结果和讨论3.1什么是在钢筋混凝土结构中大电偶和腐蚀微电池对的相对重要性？根据一些作者3,5，极化电阻作用

36、为估计钢筋混凝土中腐蚀速度提供了一个有效的方法；这个方法是非常快、方便、非破坏性、适量和相当精确的。然而，它不确定是否会对高度极化的电极产生严重的错误，通过在钢筋中的大电偶的钝化面积与激活面积的比值的影响。在作者自己对钢筋混凝土中大电偶性质的实验基础上，这些大电偶对所有的腐蚀是非常适度的，与存在充分的氧气和水分条件下腐蚀微电池对形成激活状态的钢筋比较2,7,8。因此，它已被实验验证：待添加的隐藏文字内容3(a)大电偶对潮湿混凝土中的阳极部分由一个轻微的极化作用，只要几毫伏就可以影响它的电位。(b)在另一方面，大电偶对钝化部分有一个很强的极化作用，尽管低电流的运用相对于所有腐蚀流。(c)因此，电

37、流可能会导致，非常低估在激活部分的icorr的值，因为它们通常比极化电阻值估算的icorr值的10%还小。(d)腐蚀剂会引起钢筋混凝土结构上共面的电偶，只能证明从激活面积到钝化面积边缘的一个很短的距离存在危险。图3是估算的icorr与ig值的比较，在砂浆中含有3%的cacl2，每个正极表面单元体为许多正极/负极表面比值作为美国钢铁学会304不锈钢/碳素钢电偶的一部分支持以上结论。 图3.腐蚀微电池对(icorr)和电耦合(ig)在包裹在 图4.暴露在自由氧环境下试块的icorr和ecorr不含有氯化物砂浆里的钢腐蚀中的相对意义。 的变化趋势。电流都是相对于s负极而计算得到的(在图2的电耦合中的碳素钢)。3.2钢筋腐蚀的机理是什么？当钝化状态消失，钢筋的腐蚀速度与混凝土的电阻率成反比例，在一个很宽的电阻率范围内10。因为环境中的相对湿