Corrosion Protection

Ischebeck Titan hollow bars can offer peace of mind when designing applications using the unique TITAN thread bar. Coming with a 120-year design life for permanent applications, we have a range of bars that will both meet designer requirements and give that added protection from corrosion, relying on only grout encapsulation.

When steel is left unprotected in the atmosphere, it will quickly form a brown oxide (rust) on its surface. This will continue to grow until a scale flakes from the surface; unless some external means to prevent this is provided. As the steel is required to be in place for many years, it is important that correct measures are taken to protect it. Here at Ischebeck Titan we recognise that standards suggest that designers can apply the following when designing applications using our hollow bar range:

  • additional surface coating
  • galvanizing
  • duplex
  • stainless steel (like INOX)
  • encapsulation in grout, mortar or concrete
  • plastic tubes for pile head or free length
  • a combination of the above-mentioned products

British Standard guidelines (BS8081; 1989: 8.1.2.2; 8.2.3 and Appendix A.5) propose that crack widths of <0.1mm are acceptable in a cementitious protective barrier.

Steel Characteristics

The steel used for hollow bars is a high quality, micro alloy structural steel, which has a high yield strengths and limited tensile strengths (as with strands, detailed in BS8081:1989). Unlike high tensile steel, high yield steel has a low carbon content and as a result is not susceptible to stress crack corrosion or hydrogen embrittlement. Our hollow bars are fashioned from fine-grained, S460 NH, seamless, structural steel tubes to EN 10210. The steel has notch impact resistance of approximately W = 100 Joules (at -20°C) which is higher than that of typical structural and pre-stressing steels (W = 27-15 Joules at -20°C).

Combi Coated (Epoxy) Galvanised Bar

Epoxy coatings provide optimum protection against abrasion, turbulence, corrosive fluids, and extreme temperatures. Epoxy coating is not only durable, but also resistant to many corrosive substances.

Crack Width Limitation

The Ischebeck Titan thread is coarse, widely spaced and has a groove taken out of the crown. This induces controlled cracking of the grout along the length of the bar.

Corrosion is likely to occur initially where the bar intersects a crack. Therefore, the smaller the crack width, the lower the risk of corrosion. British Standard guidelines propose that crack widths of <0.1mm are acceptable in a cementitious protective barrier. Also, BS8081:2015 recommended that further research be carried out to determine the use of crack width limitation as a form of corrosion protection.

That research has been carried out in the form of shear friction tests, in conjunction with crack width measurements, and the results have shown that the frequency of cracking within a grout body can be controlled to such an extent that the crack widths stay well below the permitted 0.1mm. In fact, the maximum crack width measured was 0.08mm compared to 0.21mm for a rope thread (R-type).

This has been determined by extensive testing and research (Report No’s. 1250/MU/2800/523dt29/07/97 & gl-2202399dd.) carried out by the LGA Geotechnical Institute, University of Munich.

Conclusion

Consideration should be given when designing applications such as soil nails that a surface coating to the bar is not always required (dependant on ground conditions). Whilst tests have concluded that the unique orientation of the threaded TITAN bar will help crack control widths to below 0.1mm, others will have to allow sacrificial allowance of the cross-sectional area and either allow for a higher capacity bar or add a surface coating. Either way, a surface coating or a sacrificial allowance will endure a higher cost. The TITAN bar will give both performance and cost savings.

If you have any questions about corrosion protection, please contact us