The reinforced concrete (RC) caissons, code-named Phoenix, still visible off the coast of Arromanches, France, have been exposed to marine immersion, tidal, splash and atmospheric conditions since 1944. Little evidence of corrosion of the steel reinforcement was observed during inspections in 2011, 2015 and 2019, although there was much structural damage. Archival material from the Second World War reveals the caissons were designed to low safety margins, without consideration of durability and constructed at a very fast rate mostly with unskilled labour, minimal material usage, without additives and no restrictions on adding water to aid concrete workability. Analysis of data that has recently become available indicates the concretes had a high cement content and were made with calcareous aggregates. It is concluded that these factors contributed to the high strength, low permeability and high remaining alkalinity of the concretes and hence to the very low evidence of reinforcement corrosion. When interpreted using recent experimental observations, these observations have implications for the design of new RC structures in marine exposures and for the prediction of the remaining life of older marine-exposed RC structures.

中文翻译：

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经过75年的海上暴露后，凤凰沉箱的增强腐蚀

自1944年以来，代号为Phoenix的钢筋混凝土沉箱，仍在法国Arromanches海岸附近可见，已经沉浸在海洋浸没，潮汐，飞溅和大气条件下。在2011年，2015年和2019年进行了检查，尽管结构上有很多损坏。第二次世界大战的档案材料显示，沉箱的设计安全系数低，不考虑耐用性，并且建造速度非常快，主要是熟练的劳动力，最少的材料使用，没有添加剂，并且没有添加水来提高混凝土的可加工性。对最近可用数据的分析表明，混凝土的水泥含量很高，是用钙质骨料制成的。结论是这些因素导致了混凝土的高强度，低渗透性和高残留碱度，因此导致钢筋腐蚀的证据非常低。当使用最新的实验观察结果进行解释时，这些观察结果对海洋暴露中新的钢筋混凝土结构的设计以及对海洋中暴露的旧钢筋混凝土结构的剩余寿命的预测都具有重要意义。