混凝土中鋼腐蝕的有關問題畢業(yè)論文外文翻譯

1、外文翻譯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.中文翻譯混凝土中鋼腐蝕的有關問題腐蝕機理和監(jiān)督、使用年限的預測和保護方法 摘要:第二部分闡述幾個仍然存在爭議的重要問題，盡管已經在混凝土中鋼腐蝕的調查研究投入了大量的工作。特別是這幾方面：1)在鋼筋混凝土結構中的大電偶和腐蝕微電池對的相對重要性；2)激活狀態(tài)的鋼筋腐蝕機理；3)阻止或停止鋼筋腐蝕最好的保護方法；4)一個鋼筋混凝土結構使用年限的可靠預測的可能

34、性探索；5)最好的防腐措施和控制方法。這些回答需要試驗得出，大部分都由作者們得出。1.前言正常條件下強堿混凝土中的鋼仍然處于鈍化狀態(tài)。鋼筋的鈍性能保證鋼筋混凝土結構無限的耐久性。然而，有一些能破壞鋼的鈍性和引起鋼筋腐蝕的實驗條件。在第部分中討論到的一些實驗結構已經引起了很多爭論1。第部分的分析雖然沒有竭盡全力，但至少是作者的意思，就像有趣的問題有不同的意見一樣。2.材料和方法讀者指出在第部分詳細描述了用于這項工作的材料和方法。這里所討論的大部分實驗結果都是從一樣的試塊和平板中得到的。電偶是由特殊設計的試塊確定的，如圖1和2所示。用一根長16m，70mm100 mm橫截面的梁模擬近真實條件。梁是

35、由每立方米350kg水泥制成，梁的一半含有添加劑，另一半含有水泥的重量的3%的cacl22，(圖1)。為了了解s正極/s負極的比值對大電偶的影響，用在一個小的碳素鋼正極環(huán)繞一個不銹鋼負極并夾緊來模擬。這樣，比值的連貫性是可靠的。此外，與鈍化結果的電位和不銹鋼的icorr是非常相似的。 圖1.梁用來分別測量混凝土中含有和不含有氯化物 圖2.用電耦合牢牢嵌入含有氯化物的砂漿里來研究的icorr和ecorr來說明鈍化鋼/活躍鋼耦合的意義。 s正極/s負極的作用和腐蝕微電池對的相對意義的方案。3.結果和討論3.1什么是在鋼筋混凝土結構中大電偶和腐蝕微電池對的相對重要性？根據一些作者3,5，極化電阻作用

36、為估計鋼筋混凝土中腐蝕速度提供了一個有效的方法；這個方法是非常快、方便、非破壞性、適量和相當精確的。然而，它不確定是否會對高度極化的電極產生嚴重的錯誤，通過在鋼筋中的大電偶的鈍化面積與激活面積的比值的影響。在作者自己對鋼筋混凝土中大電偶性質的實驗基礎上，這些大電偶對所有的腐蝕是非常適度的，與存在充分的氧氣和水分條件下腐蝕微電池對形成激活狀態(tài)的鋼筋比較2,7,8。因此，它已被實驗驗證：待添加的隱藏文字內容3(a)大電偶對潮濕混凝土中的陽極部分由一個輕微的極化作用，只要幾毫伏就可以影響它的電位。(b)在另一方面，大電偶對鈍化部分有一個很強的極化作用，盡管低電流的運用相對于所有腐蝕流。(c)因此，電

37、流可能會導致，非常低估在激活部分的icorr的值，因為它們通常比極化電阻值估算的icorr值的10%還小。(d)腐蝕劑會引起鋼筋混凝土結構上共面的電偶，只能證明從激活面積到鈍化面積邊緣的一個很短的距離存在危險。圖3是估算的icorr與ig值的比較，在砂漿中含有3%的cacl2，每個正極表面單元體為許多正極/負極表面比值作為美國鋼鐵學會304不銹鋼/碳素鋼電偶的一部分支持以上結論。 圖3.腐蝕微電池對(icorr)和電耦合(ig)在包裹在 圖4.暴露在自由氧環(huán)境下試塊的icorr和ecorr不含有氯化物砂漿里的鋼腐蝕中的相對意義。 的變化趨勢。電流都是相對于s負極而計算得到的(在圖2的電耦合中的碳素鋼)。3.2鋼筋腐蝕的機理是什么？當鈍化狀態(tài)消失，鋼筋的腐蝕速度與混凝土的電阻率成反比例，在一個很寬的電阻率范圍內10。因為環(huán)境中的相對濕