Tendons (Prestressed concrete)

Flexible fillers has recently been implemented as corrosion protection for post-tensioning
tendons used in bridge structures in Florida. There are two different explanations why
corrosion could take place: 1. water is able to reach the steel 2. Microbiologica l ly
Influenced Corrosion.
The aim of this research is to evaluate corrosion protection effectiveness of five differe nt
microcrystalline waxes under different environmental conditions. Specimens tested ranged
from 7-wire steel strands to single wires (12-16 cm). Another aim is the appraisal of wax
degradation by fungi species. Single wires coated with each of the investigated protection
materials, were sprayed with suspensions of three different fungi species and a mix of them.
For single wires, independent of the environmental condition the specimen with more
corrosion was Nontribos, as well as the filler coated wires contaminated with Fungi. Fungi
species investigated were able to utilize the waxes as carbon source and caused differe nt
extents of MIC.

Qualification criteria for cathodic protection of pre-tensioned tendon wires in concrete were studied with regard to the risks of embrittlement due to chromium microalloying and existing corrosion damage. The selected materials included two microalloyed (with 0.23 and 0.24 w% chromium) and one non-microalloyed, high carbon prestressing steels. The slow strain rate testing technique was used to evaluate the effects of polarization to -0.90 and -1.30 VSCE upon strength and ductility of the steels. Fractographic analysis was performed using scanning electron microscopy. Based upon statistical analysis, an attempt was made to relate the remaining strength of the corroded wire to the extent of corrosion damage for different corrosion morphologies.

Cathodic protection is currently recognized as the most practical mean for arresting corrosion of reinforcing steel tendons in existing concrete structures, however, its appropriateness in the case of prestressed concrete is questioned because prestressing steels are relatively susceptible to environmental cracking (hydrogen embrittlement). For the purpose of studying embrittlement tendencies a series of experiments using the slow strain rate technique were performed. The susceptibility to environmental cracking was compared for different steels corresponding to ASTM grades 270 and 250 polarized at $-$900 and $-1300$ mV (SCE) in deaerated saturated Ca(OH)$\sb2$ solutions. The influence of different notch and pit geometries was studied to simulate the behavior of corroded tendons and investigate the transition between smooth and severely notched specimen behavior. Also evaluated was the evolution of the mechanical properties of tendons after excessive polarization. The different cracking processes are discussed based on test data, fractography and exposures conditions associated with concrete structures.