CBI presents: Hot-dip galvanised reinforcing steel

In many cases, corrosion of the reinforcement due to loss of passivity as a result of progressive carbonation or the penetration of chlorides is limiting the lifespan of reinforced concrete structures In the majority of cases, the use of stainless steels is ruled out for economic reasons. Galvanized concrete steels can be an alternative.

The above-mentioned and possibly further obstacles and restrictions in the use of galvanized reinforcing steel are to be identified and systematized concerning the underlying technical questions.

The use of galvanized reinforcing steels is currently carried out in Germany based on a building authority approval. The existing problems, which are currently hindering widespread use, can be attributed to two main aspects:

– Limitations of the applicability of galvanized reinforcing steels compared to conventional reinforcement and the resulting disadvantages in design

– Limited possibilities to consider the additional benefit of galvanizing in the service life design and thus legitimize the higher production costs compared to conventional reinforcement.

The application possibilities and limits of galvanised reinforcing steel according to the approval differ in some points from those of conventional reinforcing steel. These include restrictions on bending and reverse bending, as well as restrictions on the permissible oscillation width for predominantly non-stationary loads. The latter is based on the danger of LMAC damage (Liquid Metal Assisted Cracking).

Possibilities for considering the corrosion-protective effect of galvanizing are only provided by the approval in the area of carbonation. Here, the required minimum concrete cover for exposure classes XC2, XC3 and XC4 may be reduced by 10 mm in each case. There is no provision for the possibility of providing evidence of an extended service life for a given concrete pavement compared to conventional reinforcing steel. Similarly, the protective effect for chloride-induced corrosion of reinforcement cannot be considered, although positive effects are known from the literature.

A third aspect, which goes beyond the fields of application described in the building supervisory approval, is the applicability of galvanized reinforcing steel in core-insulated building components. Stainless steels are used here today, as alkaline protection in the insulation area cannot be assumed. Galvanized reinforcing steels could also be an economical alternative here.

At this point, the CBI would like to thank the companies for their productive cooperation!