A metallurgical approach to the durability of reinforced concrete

摘要*岩盐和最近的浓盐水应用于我们的公路和桥梁是混凝土和碳钢钢筋(钢筋)高度劣化的重要原因。这种劣化是由于氯化物的进入和混凝土中钢铁表面非常薄的氧化物的分解造成的，这些氧化物通常可以保护钢铁不生锈。其结果是，温莎至蒙特利尔走廊的公路结构和停车场的盐分积累是北美任何地方最多的，相应地，劣化率也是最高的。*与此同时，《加拿大公路桥规范》已将公路桥的要求使用年限提高到75年，并提议进一步提高到100年。因此，交通当局对使用更耐腐蚀的合金作为钢筋感兴趣，以限制频繁维护的需要和相关的交通延误。尽管用这些合金加固的结构的寿命成本大大降低，但使用它们的最大障碍是初始成本。为了解决这个问题，钢铁公司正在开发使用更便宜的合金件的不锈钢牌号，但当局不愿在打算使用75年或更长时间的结构中安装未经测试的合金。欧洲和北美的一些研究小组(包括申请人的研究小组)一直在短期实验室测试中调查较新合金的相对腐蚀性能。然而，这些测试使用各种方法来加速腐蚀，通常最多包括三到五年的盐暴露，但有时只有三到四天。将加速测试的结果外推到现实世界暴露了3/4个世纪，留下了许多问题。*因此，为了更好地预测不锈钢和耐腐蚀增强合金的长期行为，拟议的研究计划的目标是确定它们嵌入混凝土并最终暴露在除冰盐中时的冶金和电化学状态。在有无氯化物的高pH环境中原位确定钝化膜的性质将是具有挑战性的，需要对传统方法进行修改。这项研究的另一个主要障碍将是在不从根本上改变条件的情况下实际实现对这些高耐蚀合金的腐蚀。需要这些数据来确定它们的腐蚀率。培训将实施这些突破性进展的下一代工程师是一个重要成果。另一个原因是，这项研究的结果将允许基础设施设计者根据当地气候的严重程度和期望的结构使用寿命，为特定的应用指定最具成本效益的材料。*中国政府**

Summary ***    The application of rock salt and, more recently, concentrated brines to our highways and bridges is instrumental in high deterioration levels of concrete and carbon steel reinforcement (rebar). The deterioration arises from the ingress of chlorides and breakdown of the very thin film of oxides on the steel surface in concrete which normally protect the steel from rusting. The result is that the highway structures and parking garages in the Windsor to Montreal corridor have the greatest accumulation of salt of anywhere in North America and correspondingly high deterioration rates. ***    At the same time, the Canadian Highway Bridge Code has increased the required service life of highway bridges to 75 years and is proposing to increase it further to 100 years. Consequently, transportation authorities are interested in using more corrosion resistant alloys as rebar to limit the need for frequent maintenance and the associated traffic delays. Despite the significantly lower lifetime costs of a structure reinforced with these alloys, the greatest obstacle to their use is the initial cost. To address this problem, steel companies are developing stainless steel grades with less expensive alloying components, but the authorities are reluctant to install untested alloys in structures intended to last for 75 years or more. A number of research groups in Europe and North America (including the applicant's) have been investigating the relative corrosion performance of the newer alloys in short-term laboratory tests. However, these tests use various methods to accelerate corrosion and typically consist of three to five years exposure to salts at most, but sometimes are as short as 3 - 4 days. Extrapolating the results of accelerated tests to real world exposure for 3/4 century leaves many questions. ***    Therefore, in order to better predict the long term behaviour of stainless and corrosion resistant reinforcing alloys, the goal of the proposed research program is to define their metallurgical and electrochemical state when they are embedded in concrete and, eventually, exposed to the de-icing salts. Determining the nature of the passive films in-situ in a high pH environment, with and without chlorides, will be challenging and require modification to traditional methods. Another major obstacle to this research will be to actually achieve corrosion in these highly resistant alloys without radically changing the conditions. These data are needed in order to determine their corrosion rates. Training the next generation of engineers who will implement these groundbreaking advances is one important outcome. Another is that the results of this study will permit infrastructure designers to specify the most cost-effective materials for particular applications depending on the severity of the local climate and the desired service life of the structure. ***    **