Product capable of inhibiting the corrosion of the reinforcement

Details Product capable of inhibiting the corrosion of the reinforcement Product capable of inhibiting the corrosion of the reinforcement

1991-01-04

1992-05-05

Dixon, Jr., William R.

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

106714, 106733, 106738, 106789, 501155, C04B 2208, E04C 501, C23F 1100

Patent

active

051103605

DESCRIPTION:

BRIEF SUMMARY
This invention deals with a product which inhibits the corrosion of reinforcements contained in concrete or cement mortar and the relative process.
The phenomenon of the corrosion of the steel of reinforced concrete is today the main worry of builders.
The steel immersed in the concrete, thanks to the strongly alkaline environment, should be protected by a passivating coat; actually in presence of perturbing external agents, with time the passivations will fail and an electrochemical process of corrosion will be started, by which oxidation products are formed at the iron-concrete interface; such products have a much greater volume, up to 6.5 times the original volume, thus producing an explosive destruction of the concrete coating of iron.
The negative effects of such a phenomenon can be specified in three different forms: sections; transformation of iron in iron oxides which may overcome the concrete's resistance to tensile stress; the reinforcing rods, such cracks being extended perpendicularly to the axis of the rods and being invisible from the outside, these crackings being able to cause sudden and unexpected breakages.
The main agents responsible for this phenomenon seem to be carbon dioxide (CO.sub.2) present in the air and the chlorides; to these the occasional facts due to particular environmental situations can be added.
The CO.sub.2 causes, penetrating by diffusion or partial overpressure through the pores of the concrete, a transformation reaction of the hydroxides in carbonates:
When the phenomenon reaches the steel, areas lacking protection are formed in which presumably the iron dissolves like Fe (II) and precipitates again as hydroxide, thus starting the formation of the so called rust.
The chlorides are instead present in the aggregates, in the water contained in the cast concrete and can also penetrate from the outside. When they reach the steel by diffusion they break the passivating superficial coat starting an electrochemical process in which the anode is the surface of the no longer passivated steel and the cathode is the remaining passivated surface.
Macroscopic examples of the degradation which has been described can be found in the areas where chlorinated products are used to prevent the ice formation and in areas which are in some way influenced by a sea environment.
At the present time in order to prevent this phenomenon specific additives are used which slow down the corrosion, like for example, the addition of products capable of forming a passivating coat on the steel.
U.S. Pat. No. 2,879,578 relates to a method of rust-proofing concrete reinforcing elements which comprises coating the reinforcing elements with a composition containing barium chromate.
BE-A-568 543 discloses a process for the preparation of an anti-corrosive coating having to be applied on metals and comprising zinc chromate and Portland cement.
Both the cited known methods have the drawback that the protecting compositions have to be applied directly to the metal structure and further coated with a second layer: it is evident that such a method would be very expensive and time consuming and could not be industrially applied without great drawbacks and technical problems.
The aim of this invention is that of providing an inhibitor of the corrosion of the reinforcements contained in concrete or cement mortar which can be easily and economically obtained and just as easily used.
It has now been discovered that a by-product of the production of chromates is surprisingly good at inhibiting the corrosion of the reinforcements contained in concrete or cement mortar. Such a product is consisted of "exhausted chromite earths" i.e. those earths that are formed by roasting mixes containing chromite ores at high temperatures (500.degree.-1300.degree. C.), and a successive thermal treatment by immersion in water or aqueous solutions at room temperature (leaching).
As is commonly known, further to chromite ores such mixes can contain also other chromium III containing compounds, such as exhausted, old or broken refractorie

REFERENCES:
patent: 2374562 (1945-04-01), Owens
patent: 2879578 (1959-03-01), Ulystedt
patent: 4504321 (1985-03-01), Kapland et al.

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