From earlier linkBeaker wrote:from where ?kinard wrote:Sufficient current already in rebar, effectively a circuit.Beaker wrote:anode will do nothing without current.kinard wrote:Still have to remove blown concrete and rust flake, coat with bitumen and box up for filling.Beaker wrote:And how do you treat the rust without removing the concrete ?
.Introducing an anode into the rebar circuit ensures the rebar rust site is no longer the anode.zincs prevent rust but don't magically remove it
Corrosion of rebar
The corrosion of steel rebar, the strengthening in concrete, is an electrochemical process. Electrons are
exchanged between rebar, water and oxygen. The energy for this circuit is derived from the rebar. The origin of iron is iron ore, a natural form of oxidized iron. A high amount of energy is used in blast furnaces to turn iron ore into iron, this energy is stored in the metal and the metal wants to be transformed back to its original form, therefore it needs to transfer its energy. The circuit runs partially through the rebar and partially through pore water in the concrete. Where (positive) current leaves the rebar, so called anode
places, corrosion takes effect: iron dissolves and rebar is affected. Where the circuit enters the rebar, so called cathode places, oxygen reacts with water creating hydroxide, an innocent byproduct. Draining the
“steel concrete battery” leads to corrosion causing problems in concrete because of the expansion of the
steel material and increasing pressure on the concrete.
Two ways of Cathodic Protection
Cathodic Protection
of rebar in concrete can be applied in two different ways:
Galvanic (GCP) or through Impressed Current (ICCP).
Galvanic Cathodic Protection
(GCP)
Galvanic Cathodic Protection uses anodes made from lesser base material than the rebar. When connected to each other the anode will oxidize instead of the rebar, therefore the term sacrificial anode is used for anodes making use of this principal, the anode sacrifices itself for rebar.
Impressed Current Cathodic Protection
(ICCP)
Cathodic Protection based on Impressed Current makes use of the electro part of the electrochemical corrosion process. By placing anodes in or on the concrete and connecting a direct current power source
between the anode and rebar in the concrete a potential difference has been created, Ions will be transferred through the concrete and the rebar is forced into a cathodic position, hence halting the corrosion.