外文翻譯--混凝土中鋼腐蝕的有關(guān)問題-文庫吧資料
2025-01-13 09:24本頁面
【正文】 oxygen reduction. 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 have led to a wide range of diffusivity values (from 10 12 to 10 8 m2/s) for oxygen in cement paste [14]. Since the diffusion coefficient of oxygen in aqueous solutions (1)O2 = 10 5 cm2/s1), is saturation concentration (CO2 = x 10 7 mol/cm 3) and the approximate thickness of diffusion layers in stagnant solutions (8 = 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 (96,500 ). For 1cm 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 = laA/cm 2, which is quite consistent with the icorr values estimated under pore saturation conditions at the end of the curing process, 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 inpatible with the rates allowed by the limiting diffusion current of oxygen. Therefore, in some circumstances, alternative cathodic processes allowing for faster kiics must therefore be involved. In recent work, the concurrence of crevices, chloride ions and dissolved oxygen at the steel/concrete interface was claimed to 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 ratedetermining step, namely: Under some circumstances, once corrosion in an active state has 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 ico~r over a wide resistivity range 。 the method is quite rapid, convenient, nondestructive, quantitative and reasonably precise. However, it is uncertain whether it may give rise to serious errors with highlypolarized electrodes by the effect of passive/active area galvanic macrocouples in the reinforcements [6]. Based on the authors39。 and 5) the best corrosion measurement and control methods. The responses provided are supported by experimental results, most of which were obta
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