Corrosion of Unbonded Prestressing Tendons

The causes and effects of corrosion of unbonded single strand tendons are, in several respects, different fixnn those of bonded conventional reinforcing or other post-tensioning systems. Thus, the methods for evaluating and repairing corrosion of single strand tendons are also different in some respects.  

For example, since the tendons are laigely isolated from the surrounding concrete, they may not be affected by deleterious materials, such as chlorides and moisture in the concrete. However, they also are not passivated by the surrounding concrete and can corrode if water gains access to the inside of the sheathing or anchorage and the grease protection is inadequate. 

Measures taken to repair and protect the surrounding concrete may not repair or reduce deterioration of the prestressing steel where corrosion has been initiated. The tendons usually require separate evaluation and repair. 

Unbonded tendons in the early systems used bundles of wires or strands, sometimes inaccurately called cables, of various diameters and protected by grease and paper sheathing that were sometimes applied by hand. 

For many types of structures, these advantages included shorter construction time, reduced structural depth, increased stiffness and savings in overall cost. In addition to their use in 

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