Basic Study on Cathodic Protection for Repairing of Prestressed-Concrete Structures Damaged by Chloride Corrosion of Reinforcement

阴极保护有望成为海洋环境下新修混凝土结构的实用防腐体系。为了建立高可靠性的预应力混凝土结构修复阴极保护，本文进行了一些室内和现场试验。结果表明：(1)对混凝土中钢筋的防腐，不能满足-100mV的阴极保护位移判据。在海洋环境中大气干湿循环等严重腐蚀环境中，可能需要150-200mV去极化才能停止腐蚀。(2)在对预应力混凝土结构进行阴极保护的情况下，当电流密度超过保护水平时，预应力混凝土链的强度有降低的可能，并且在该电流密度水平下，由于析氢高压，混凝土也可能发生开裂。因此，无论混凝土和周围大气状况如何，对预张式预应力混凝土结构都不应绝对过度保护阴极保护。(3)通过阴极保护修复钢筋混凝土车库的现场试验，证实了阴极保护对受干燥影响时间较长的混凝土结构是有用的。腐蚀混凝土结构的阴极保护修复效果影响钢筋的均匀抛光状态。(4)开发了混凝土结构阴极保护带阳极的永久形式，简化了阳极体系结构，提高了其耐久性。

Cathodic protection is expected to be a practical corrosion protection system for newly and repaired concrete structures in marine environment. In this study, some laboratory and field examinations were carried out for the establishment of high reliability on the cathodic protection for repairing prestressed-concrete structures. The following results were obtained :(1) -100mV shifting criterion for cathodic protection can not be accomplished satisfactorily for corrosion protection of reinforcements in concrete. 150-200mV depolarization may be necessary to stop the corrosion in severe corrosion environment such as atmospheric dry and wet cyclic condition in marine environment.(2) In the case of cathodic protection on prestressed-concrete structures, the possibility of reduction of strength of prestressed-concrete strand is found at over-protection-level current density, and cracking of concrete may also occur at that current density level, due to the high pressure of hydrogen evolution. Therefore, it is necessary that cathodic protection should not be over-protected absolutely on pretension type prestressed-concrete structures, regardless of condition of concrete and surrounding atmosphere.(3) From the field examination of repairing the reinforced-concrete garage by the cathodic protection, it is confirmed that the cathodic protection can be useful on concrete structures affected by drying for relatively long time. And even polish condition of reinforcement is influenced by the repairing effect of cathodic protection of corroded concrete structures.(4) The permanent form with anode of cathodic protection on concrete structures is developed, as the anode system construction is simplified and its durability is enhanced.