外文翻譯--混凝土中鋼腐蝕的有關(guān)問題

1、<p><b>　　外文原文II:</b></p><p>　　Some questions on the corrosion of steel in concrete.</p><p>　　Part Ⅱ: Corrosion mechanism and monitoring, service</p><p>　　life predi

2、ction and protection methods</p><p>　　J.A. Gonzdlez , S. Felifd, P. Rodffguez , W. Lfpez , E. Ramlrez , C. Alonso , C. </p><p><b>　　Andrade </b></p><p><b>　　ABSTRA

3、CT</b></p><p>　　This second part addresses some important issues that remain controversial despite the vast amounts of work devoted to investigating corrosion in concrete-embedded steel. Specifically,t

4、hese 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

5、 methods for preventing or stopping reinforcement corrosion; 4) the possibility of a reliable p</p><p>　　1. INTRODUCTION</p><p>　　Concrete-embedded steel is known to remain in apassive state und

6、er 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

7、 that disrupt 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 analyse<

8、/p><p>　　2. MATERIALS AND METHODS</p><p>　　The 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 her

9、ein were obtained with the same types of specimens and slabs.Galvanic couples were determined on speciallydesigned specimens, such as those shown in Figs. 1 and 2.Near-real conditions were simulated by using a beam that

10、was 160cm long and 7 x 10 cm in cross-section. The beam was made from 350 kg cement/m 3, half of which</p><p>　　contained no additives, while the other half included 3% CaC12 by cement weight [2], (Fig. 1).

11、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</p><p>

12、　　(Fig. 2). In this way, the ratio's consistensy was assured. In addition, the potential and icorr of stainless steal and those of the passive structures were very similar.</p><p>　　Fig. 1 - Beam used to

13、 measure icoTr and Ecorr in Fig. 2 - Scheme of galvanic macrocouples embedded</p><p>　　concrete with and without chlorides and to in chloride- containing mortar used to study the</p><p

14、>　　illustrate the significance of passive steel/active effect of the Sanod/Scathod ratio and their relative</p><p>　　steel macrocouples. significance to corrosion micro

15、cells.</p><p>　　3. RESULTS AND DISCUSSION</p><p>　　3.1 What is the relative significance of galvanic macrocouples and corrosion</p><p>　　microcells in RC structures ?</p><

16、;p>　　According 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, quan

17、titative and reasonably precise. However, it is uncertain whether it may give rise to serious errors with highly-polarized electrodes by the effect of passive/active area galvanic</p><p>　　macrocouples in th

18、e reinforcements [6].</p><p>　　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 t

19、o that of 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:</p><p>　　(a) Galvan

20、ic macrocouples have a slight polarizing effect on anodic areas in wet concrete, whose potential is thereby influenced in only a few millivolts.</p><p>　　(b) On the other hand, macrocouples have a strong pol

21、arizing effect on passive areas despite the low galvanic currents involved relative to the overall corrosion current.</p><p>　　(c) As a result, galvanic currents can result in grossly underestimated icorr va

22、lues for the active areas since they are often smaller than 10% of the ico= values estimated from polarization resistance measurements.</p><p>　　(d) The corrosive effect ofcoplanar macrocouples on RC structu

23、res only proves dangerous within a small distance from the boundary of active and passive areas.</p><p>　　Fig. 3 compares the estimated icorr and ig values, in mortar containing 3 o~ A CaC12, per anode surfa

24、ce unit for a number of anode/cathode surface ratios for AISI 304 stainless steel/carbon steel macrocouples in support of the above conclusions [9].</p><p>　　3.2 By what mechanism do reinforcements corrode i

25、n an active state ?</p><p>　　When the passive state is lost, the rate of reinforcement corrosion in inversely proportional to the resistivity of concrete over a wide resistivity range [10]. Because </p>

26、;<p>　　Fig. 3 - Relative significance of corrosion microcells Fig. 4 - Trends in ico. and Ecorr for</p><p>　　(icorr) and galvanic macrocouples (i.) in corrosion specimens exposed to an oxyg

27、en-free </p><p>　　of steel embedded in mortar containing no chloride. environment.</p><p>　　Both currents were calculated relative to Sanod</p><p>　　(carbon steel in the macro

28、couples of Fig. 2).</p><p>　　the environment's relative humidity and ionic additives of concrete determine concrete resistivity, these factors, together with oxygen availability at reinforcement surfaces

29、,control the corrosion rate [11].</p><p>　　The electric resistivity of water-saturated concrete structures is relatively very low, and the corrosion rate is believed to be essentially controlled by the diffu

30、sion of dissolved oxygen through the concrete 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.</

31、p><p>　　The significance ascribed to the role of oxygen justifies the efforts to determine its diffusion coefficient in concrete[12, 13]. The variety of methods and experimental conditions used for this purpose

32、 have led to a wide range of diffusivity values (from 10 -12 to 10 -8 m2/s) for oxygen in</p><p>　　cement paste [14].</p><p>　　Since the diffusion coefficient of oxygen in aqueous solutions (1)O

33、2 = 10 -5 cm2/s-1), is saturation concentration (CO2 = 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 calc

34、ulated as :</p><p>　　ilo2 = - z FD02C02/r = 8 x 10 -4 A/cm 2 (80 pA/cm 2)</p><p>　　where z is the number of equivalents per mole (4) and F the Faraday (96,500 A.s/eq).</p><p>　　For

35、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

36、estimated under pore saturation conditions at the end of the curing</p><p>　　process, both for mortars containing no chloride ions and for those including 2, 4 or 6% C1- [16].</p><p>　　On the ot

37、her 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 allowed by the limiting di

38、ffusion 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 dissolve

39、d oxygen at the steel/concrete interface was claime</p><p>　　There are a number of facts that refute oxygen reduction as being the sole corrosion rate-determining step, namely: </p><p>　　- Under

40、 some circumstances, once corrosion in an active</p><p>　　state has started, it develops at the same rate even though oxygen is being removed from the medium (Fig. 4) [11].</p><p>　　- As saturat

41、ion of concrete pores decrease, concrete resistivity controls ico~r over a wide resistivity range ; therefore, the corrosion rate seems to decrease in proportion to the ease with which oxygen penetrates into the structur

42、e(Fig. 5)[10].</p><p>　　On the other hand, there are several arguments in favour of proton reduction in Ca(OH)2-saturated solutions or cement mortars [11] :</p><p>　　- The pH decreases from 12.6

43、 to ca. 5 within crevices at the steel/electrolyte interface upon exposure of the steel to a Ca(OH)2-saturated solution with C1- additions and wellaerated. If sufficient oxygen is available, the pH can drop as low as 1-2

44、.</p><p>　　- 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).</p><p>　　- Th

45、e formation 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. Eve

46、rything points to pits with a low enough pH for the anodic current applied to overlap with a corrosion process involving proton reduction as a cathodic half-reaction.</p><p>　　When concrete-embedded steel is

47、 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 environment's relative humidity increases [18]

48、. 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).</p&g

49、t;<p>　　Fig. 5 - Relationship between mortar resistivity Fig. 6 - Influence of the degree of pore saturation</p><p>　　and the corrosion rate of reinforcements. on the corrosion rate of rei

50、nforcements.</p><p><b>　　中文翻譯II:</b></p><p>　　混凝土中鋼腐蝕的有關(guān)問題</p><p>　?、颍焊g機(jī)理和監(jiān)督、使用年限的預(yù)測(cè)和保護(hù)方法</p><p>　　J.A. Gonzdlez , S. Felifd, P. Rodffguez , W. Lfpez , E.

51、Ramlrez , C. Alonso , C. </p><p><b>　　Andrade </b></p><p>　　摘要:第二部分闡述幾個(gè)仍然存在爭(zhēng)議的重要問題，盡管已經(jīng)在混凝土中鋼腐蝕的調(diào)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(jié)構(gòu)中的大電偶和腐蝕微電池對(duì)的相對(duì)重要性；2)激活狀態(tài)的鋼筋腐蝕機(jī)理；3)阻止或停止鋼筋腐蝕最好的保護(hù)方法；4)一

52、個(gè)鋼筋混凝土結(jié)構(gòu)使用年限的可靠預(yù)測(cè)的可能性探索；5)最好的防腐措施和控制方法。這些回答需要試驗(yàn)得出，大部分都由作者們得出。</p><p><b>　　1.前言</b></p><p>　　正常條件下強(qiáng)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(jié)構(gòu)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(shí)驗(yàn)條件。在第Ⅰ部分中討論到的一些實(shí)驗(yàn)結(jié)構(gòu)已經(jīng)引起

53、了很多爭(zhēng)論[1]。第Ⅱ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。</p><p><b>　　2.材料和方法</b></p><p>　　讀者指出在第Ⅰ部分詳細(xì)描述了用于這項(xiàng)工作的材料和方法。這里所討論的大部分實(shí)驗(yàn)結(jié)果都是從一樣的試塊和平板中得到的。電偶是由特殊設(shè)計(jì)的試塊確定的，如圖1和2所示。用一根長(zhǎng)16m，70mm×

54、100 mm橫截面的梁模擬近真實(shí)條件。梁是由每立方米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CaCl2[2]，(圖1)。為了了解S正極/S負(fù)極的比值對(duì)大電偶的影響，用在一個(gè)小的碳素鋼正極環(huán)繞一個(gè)不銹鋼負(fù)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(jié)果的電位和不銹鋼的icorr是非常相似的。</p><p>　　圖1.梁用來分別測(cè)量混凝土中含有和不含有氯化物 圖2.用電

55、耦合牢牢嵌入含有氯化物的砂漿里來研究</p><p>　　的icorr和Ecorr來說明鈍化鋼/活躍鋼耦合的意義。 S正極/S負(fù)極的作用和腐蝕微電池對(duì)的相對(duì)意義的方案。</p><p><b>　　3.結(jié)果和討論</b></p><p>　　3.1什么是在鋼筋混凝土結(jié)構(gòu)中大電偶和腐蝕微電池對(duì)的相對(duì)重要性？</p><

56、;p>　　根據(jù)一些作者[3,5]，極化電阻作用為估計(jì)鋼筋混凝土中腐蝕速度提供了一個(gè)有效的方法；這個(gè)方法是非?？?、方便、非破壞性、適量和相當(dāng)精確的。然而，它不確定是否會(huì)對(duì)高度極化的電極產(chǎn)生嚴(yán)重的錯(cuò)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。</p><p>　　在作者自己對(duì)鋼筋混凝土中大電偶性質(zhì)的實(shí)驗(yàn)基礎(chǔ)上，這些大電偶對(duì)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(duì)形成激活狀態(tài)

57、的鋼筋比較[2,7,8]。因此，它已被實(shí)驗(yàn)驗(yàn)證：</p><p>　　(a)大電偶對(duì)潮濕混凝土中的陽(yáng)極部分由一個(gè)輕微的極化作用，只要幾毫伏就可以影響它的電位。</p><p>　　(b)在另一方面，大電偶對(duì)鈍化部分有一個(gè)很強(qiáng)的極化作用，盡管低電流的運(yùn)用相對(duì)于所有腐蝕流。</p><p>　　(c)因此，電流可能會(huì)導(dǎo)致，非常低估在激活部分的icorr的值，因?yàn)樗鼈兺ǔ?/p>

58、比極化電阻值估算的icorr值的10%還小。</p><p>　　(d)腐蝕劑會(huì)引起鋼筋混凝土結(jié)構(gòu)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(gè)很短的距離存在危險(xiǎn)。</p><p>　　圖3是估算的icorr與ig值的比較，在砂漿中含有3%的CaCl2，每個(gè)正極表面單元體為許多正極/負(fù)極表面比值作為美國(guó)鋼鐵學(xué)會(huì)304不銹鋼/碳素鋼電偶的一部分支持以上結(jié)論。</p>&l

59、t;p>　　圖3.腐蝕微電池對(duì)(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</p><p>　　不含有氯化物砂漿里的鋼腐蝕中的相對(duì)意義。 的變化趨勢(shì)。</p><p>　　電流都是相對(duì)于S負(fù)極而計(jì)算得到的(在圖2的電耦合中的碳素鋼)。</p><p>　　3.2鋼筋腐蝕的機(jī)理

60、是什么？</p><p>　　當(dāng)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(gè)很寬的電阻率范圍內(nèi)[10]。因?yàn)榄h(huán)境中的相對(duì)濕度和混凝土的離子型外加劑確定混凝土的電阻率，這些因素與氧氣一起在鋼筋的表面控制著腐蝕速度[11]。</p><p>　　飽和水混凝土結(jié)構(gòu)的電阻率是相對(duì)非常低的，而且腐蝕速度實(shí)際上是溶解氧的擴(kuò)散控制的，通過混凝土包住鋼筋實(shí)現(xiàn)。這與在中性和強(qiáng)堿條件下唯一可能

61、的負(fù)極反應(yīng)是氧氣的還原作業(yè)這個(gè)理念是一致的。</p><p>　　這個(gè)重要性歸因于氧氣的循環(huán)作業(yè)，它證明這些作用對(duì)確定它在混凝土中的擴(kuò)散率是正確的[12,13]。各種方法和實(shí)驗(yàn)條件用于這個(gè)目的，已得出了一定范圍的水泥漿中的氧氣的擴(kuò)散率(從10-12到10-8m2/s)[14]。</p><p>　　因?yàn)樗芤?CO2=10-5cm2/s-1)中氧氣的擴(kuò)散率是飽和濃度(CO2=2.1

62、5;10-7mol/cm3)，不流動(dòng)環(huán)境中(=0.001cm)擴(kuò)散層的近似密度，都是眾所周知的，這個(gè)有限擴(kuò)散流可以這樣計(jì)算：</p><p>　　其中z是等價(jià)的每摩爾(4)的數(shù)值，而F就是法拉第(96,500As/eq)。</p><p>　　平均孔隙率為15%的1cm厚的砂漿保護(hù)層厚度與擴(kuò)散層厚度一樣，與在養(yǎng)護(hù)期的最后空隙飽和條件下估算得的icorr值是非常一致的，這些砂漿不含氯化物離子

63、而都含有2,4或6%的Cl-[16]。</p><p>　　另一方面，ca.10A/cm2的icorr(見第Ⅰ部分圖9)[4]已經(jīng)由一些作者從含氯化物的砂漿或碳酸鹽砂漿與氧氣有限的擴(kuò)散流所允許的速度是不協(xié)調(diào)的。因此，在一些環(huán)境下，替代負(fù)極的過程必須有更快的動(dòng)力。在最近的工作中，裂縫、氯化物例子和溶解氧并存在鋼與混凝土的交界面，可以為質(zhì)子的還原和替換機(jī)理的發(fā)生提供熱動(dòng)力條件[11,17]。</p>&

64、lt;p>　　有很多論據(jù)反駁氧氣的還原作用作為底面腐蝕的定速步驟，即：</p><p>　　— 在一些環(huán)境下，腐蝕一旦開始，它發(fā)展到同一個(gè)速度盡管氧氣正在從媒介中排除(圖4)[11]。</p><p>　　— 當(dāng)混凝土空隙飽和作用降低，混凝土的電阻率控制icorr在一個(gè)寬泛的電阻率范圍內(nèi)；因此，腐蝕速度的減小好像與氧氣進(jìn)入結(jié)構(gòu)的難易成反比例(圖5)[10]。</p>&

65、lt;p>　　在另一方面，有一些論點(diǎn)支持在飽和Ca(OH)2中或水泥砂漿中的質(zhì)子還原反應(yīng)[11]：</p><p>　　— PH值由12.6減小到ca.5在暴露的含有Cl-的飽和Ca(OH)2中的鋼與電解質(zhì)溶液的交界面上。如果提供充足的氧氣，PH值可以降低到1-2。</p><p>　　— 從在潮濕的空氣中含有氯化物的砂漿試塊的裂縫和大空隙中暴露的PH值1-5的酸性分泌物，腐蝕速度很

66、快(5-10A/cm2)。</p><p>　　— 在蝕坑處涂上氫氧化鐵膜的鋼在含有氯化物的飽和Ca(OH)2中極化成陽(yáng)極時(shí)會(huì)產(chǎn)生氣泡，因?yàn)殡娢坏慕档托枰尫叛鯕?。每一個(gè)蝕坑點(diǎn)有一個(gè)足夠低的PH，因參與質(zhì)子還原反應(yīng)就像陰極半反應(yīng)，它們的腐蝕過程與陽(yáng)極流互相重疊。</p><p>　　當(dāng)包裹在混凝土中的鋼處于腐蝕狀態(tài)，它的腐蝕動(dòng)力指數(shù)隨著空隙飽和作用的上升而升高(圖6)，就像裸露在大氣中的鋼