外文翻譯--混凝土中鋼腐蝕的有關(guān)問題(編輯修改稿)
2025-02-04 20:58 本頁面
【文章內(nèi)容簡(jiǎn)介】 ico. and Ecorr for (icorr) and galvanic macrocouples (i.) in corrosion specimens exposed to an oxygenfree 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 environment39。s relative humidity and ionic additives of concrete determine concrete resistivity, these factors, together with oxygen availability at reinforcement surfaces,control the corrosion rate [11]. The electric resistivity of watersaturated concrete structures is relatively very low, and the corrosion rate is believed to be essentially controlled by the diffusion 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. 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].
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