Corrosion of reinforcing steel and post-tensioned steel in concrete

混凝土的抗压强度很强，但在拉伸荷载下很容易开裂。在钢筋混凝土结构中，钢筋限制了这些裂缝的宽度；然而，裂缝的存在使钢筋容易受到腐蚀。后张法的发明是为了克服混凝土在拉伸状态下的弱点。与传统的钢筋混凝土结构相比，后张法除了最大限度地减少混凝土的裂缝外，还减少了混凝土和钢材的使用量，这是经济和环保的。所有嵌入混凝土中的钢材在表面形成一层保护膜，类似于在不锈钢上形成的保护膜，以保护其免受腐蚀。然而，在加拿大，钢筋混凝土失效的最常见原因是钢筋的腐蚀。这是因为除冰盐或海洋大气中的氯化物通过水泥浆中的气孔和裂缝渗透到混凝土中，破坏了钢材上的保护膜。虽然有大量关于氯化物渗透到完好的混凝土中以及由此产生的腐蚀过程的研究，但关于裂缝在加剧这些过程中的作用以及后张拉系统在暴露在盐分中时表现如何，人们知之甚少。

Concrete is strong in compression but readily cracks under tensile loads. In reinforced concrete structures, reinforcing bars limit the width of these cracks; however, the presence of cracks makes the bars susceptible to corrosion. Post-tensioning was invented to combat the weakness of concrete under tension. In addition to minimizing cracking in the concrete, post-tensioning reduces the amount of concrete and steel used compared to the conventional reinforced concrete structures, which is economically and environmentally beneficial. All steel embedded in concrete develops a protective film on the surface similar to that which forms on stainless steel and which protects it from corrosion. Nevertheless, the most common cause of failure of reinforced concrete in Canada is corrosion of the reinforcing steel. This is because chlorides from de-icing salts or marine atmospheres penetrate the concrete through pores and cracks in the cement paste and destroy the protective film on the steel. While there is a large body of research on the penetration of chlorides into sound concrete and the resultant corrosion process, much less is known about the role of cracks in exacerbating these processes and how the post-tensioning system fares when exposed to salts.