Corrosion of reinforcing steel and post-tensioned steel in concrete

混凝土在压缩时很结实，但在拉伸荷载下很容易开裂。在钢筋混凝土结构中，钢筋限制了裂缝的宽度；然而，裂纹的存在使棒材容易受到腐蚀。后张拉是为了克服混凝土在受拉作用下的弱点而发明的。除了最大限度地减少混凝土开裂外，与传统的钢筋混凝土结构相比，后张拉减少了混凝土和钢材的使用量，这在经济和环境上都是有益的。所有嵌入混凝土中的钢材都会在混凝土表面形成一层保护膜，这与不锈钢表面形成的保护膜类似，从而保护混凝土免受腐蚀。然而，在加拿大，钢筋混凝土最常见的失效原因是钢筋的腐蚀。这是因为除冰盐或海洋大气中的氯化物通过水泥浆中的孔隙和裂缝渗透到混凝土中，破坏了钢的保护膜。虽然对氯化物渗透到健全混凝土中以及由此产生的腐蚀过程进行了大量研究，但对裂缝在加剧这些过程中的作用以及暴露于盐时后张紧系统的表现知之甚少。

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.