Hot Dipped Galvanized Steel Rebar Versus Fiberglass Rebar (GFRP)
Galvanized Steel and other metals (except gold) are inherently unstable. This instability is what drives the corrosion process. Metals are continually trying to revert to their natural state as an elemental mineral. Some metals corrode faster than others. As metal corrodes it expands. In concrete this causes degradation resulting in loose bonding, spalling, cracking and breakage.
Hot dipped galvanized rebar relies on a sacrificial zinc coating to protect the underling black steel rebar from rusting. Although it has occasionally been credited with extending the life of concrete structures, it often has had little or even a negative impact on concrete life. Current government funded studies both in Canada and the U.S. indicate a life expectancy of 20 years with galvanized reinforced concrete. (Excerpts from current studies links are listed below).
A 23-year-old bridge deck reinforced with Galvanized rebars suffering from corrosion induced cracking.
This may be related to zinc’s high reactivity with alkali which is found in concrete. In certain applications, the by-products of the reaction will cause coating expansion rates of up to 260%. This effect may be as damaging to concrete as surface rust (see diagram below).
Corrosion Cycle of Steel Rebar
All types of steel will eventually rust causing premature degradation of concrete structures. GFRP eliminates the corrosion cycle.