US2879578A - Method of rust-proofing concrete reinforcing elements - Google Patents

Description

United States Patent METHOD OF RUST-PROOFIN G CONCRETE REINFORCIN G ELEMENTS Leo Torstenv Ulfstedt, Sodertalje, Sweden, assignor, by mesne assignments, to Casius Corporation Limited, Montreal, Quebec, Canada No Drawing. Application May 14, 1953 Serial No. 355,173.

Claims'priority, application Sweden'March'l3,,1953* 4 Claims. (C1. 25-154) This invention relates to a method of rust-proofing iron and steel. reinforcing elements intendedv to be. cast into concrete or similar structures.

For this purpose, methods of providing reinforcing elements with a coating. of a mineral composition, for example by treating the elements. with. acement-containing grout, silicate-containing.solutionsor thelike, are already known. Such. coatings. may be very-efiective, but they do not give..an..absolute. protection againstrust, since they function only by preventing, more or less, owingto their tightness, the admission. of oxygen to the reinforcing elements, thus retardingrust-formation.

In order to improve the rust-preventing. effect ofsuch mineral coatings, it has been proposed to adinix to the coating compositibnpot'assium chromate or other soluble chromates, in the presence of which iron cannot rust, due to the passivating effect of'thechromates ions on the iron. The use. of suchchromates has. two. drawbacks, however. Firstly, from the sanitary point of. view the use of chromate solutions suffers from the disadvantage that the workers handling the solutions often contract very troublesome allergic'diseases. Secondly, it is uncertain whether the soluble chromate remains in the rust-protective coating for a sufficient time, as it is easily spread and dis t'ribut'ed in the concrete owing to the wandering of moisture in the reinforced concrete structure, so that the. concentration of chromate ions around the. irons maysoon be insuflicient to produce. the intended effect.

According to thepresent invention the drawbacks and inconveniences indicated above are eliminated by adding the chromate in the form of the extremely ditlicultly soluble barium chromate;

The invention is basedzonsthe factsfthatibarium sulfate is still less: soluble. than barium: chromate, while alkali metall chromates as"v well as: calcium chromate. are easily soluble, and further" that: the: hydraulic and other. masses,

into which reinforcing: elementsare generally embedded, generally contain sulfates, or without any inconvenience may be mixed: with a. small quantity of sulfates, whereby a successive conversion of the barium chromate with formation of barium sulfate. and an easily'soluble. chroit will not contain chromate. ions; in concentrations dan-- gerous to health. When the elements after. the' application of' the coating'thereonand. drying the; coating. have been cast into sulfate-containing concrete, or sulfate-containing masses of similar kind, the water. present in the mass (concrete), which always contains small amounts of sulfate dissolved: therein, penetrates. into the rust-protective coating, whereby the barium chromate contained'in the coating reacts extremelyslowly with the'sulfate. This 1 results inth'eprecipitation of barium-sulfate and the formation of a-sol'ublechroma'te, whereby" the chromaterom concentration'risesto values sufficient to secure a passivat-ion of the reinforcing irons. If the cast mass, when set, is allowed or caused. to dry completely, obviously this conversion is discontinued, but at the same time alsothe main cause of rust-formation is eliminated, no moisture being present. If the. concrete. should later absorb moisture, sulfate is again capable of diffusing onto the barium chromate. in thecoating on the irons, whereby thechromate. ion-concentration requiredfor passivating theirons is again restored.

Y The content of sulfate required in. the mass into which the. reinforcing elements provided with a barium chromate-containing coating according to theinvention are. to be cast,.-need not be great. It has. been found in the case of commoncement concrete, the binder of which is Portland cement. containing sulfate corresponding to 1-3% 1 to add to thecoating compositionmay vary within comparatively wide limits. In view of the fact that even very low chromate ion-concentrations are sufiicient; to produce the desired passivating. effect. of the. reinforcement irons,

. and sincethe relatively small difference in the solubility of the. barium. chromate and the. barium, sulfate results in a very slow formation of. chromateions, evena comparatively low content. of bariumtchromate in the. coating issufficient to secure the maintenance of the required chromate ion-concentration in the neighbourhood of the reinforcing elements for a very long period of time. Further, as already indicated above, when the cast concrete has set and its moisture content has decreased, the possibilities of the diffusion of sulfate ions as well as chromate ions are reduced, which results simultaneously in a retarded production and a-retarded removal of chromate ions.

With regard to the above-mentioned facts, even. a barium-chromate content of. about 1%, based on the solid components in the coating composition, is often sufficient and suitable for obtaining the desired effect. However, in certain cases it may be preferable to. add the. barium chromate in a considerably higher concentration, especially in the case of'concrete structures which are exposed to the strong influence of moisture over long periods. Thus the barium chromate content in such cases may amount I05, 1 0, 20 or even 40-50% of the other solid components in the coating composition.

Apart from thecontent of barium chromate, the coatingcomposition according to theinvention may be composed in any suitable manner, for example as disclosed and claimed in. my and Simonssons joint prior US.

.coating remains reactive with water and unites with concrete in which the coated reinforcing elements. are subsequently embedded, as described in the above-mentioned patents; As examples of such binding agents may lulose.

forming calcium silicates, as described in the Patent No. 2,611,945.

As is well-known, common, dense cement concrete constitutes in itself a comparatively effective rust-protection for the reinforcing irons embedded therein. However, this is not the case with light-weight concrete, and for this'reason the application of the invention has its greatest importance in connection with concrete of the latter kind. 'By light-weight concrete according to the application is to be understood concrete which has been produced from light aggregate together with the usual binders, as well as concrete which has been manufactured by producing pores in the concrete mass by the addition of gas-developing of foam-producing agents, independently of whether the light-weight concrete thus produced is then left to set under the influence of moisture and air,

or steam-cured by means of pressure-steam, for example at an over-pressure of 8-12 kgs. In the latter case, the

application of the invention has been found to be especially favourable, in so far as it has proved thatthe sulfate-content in steam-cured concrete is generally present in a very easily soluble form.

When carrying out the invention in practice, the mineral coating composition containing barium chromate is first prepared by mixing the components together to a homogenous liquid, preferably aqueous suspension. The iron or steel reinforcing elements are then coated with the resulting grout or slurry in any suitable manner, for example by dipping, brushing, spraying or other methods. The coating thus applied is thereupon dried by exposing it to the air or, if it is desired to accelerate the drying, to a current of heated air of a temperature of about C., for example.

The so-coated reinforcing elements are embedded in concrete, light-weight concrete or like masses and the coating is united with the concrete during setting or steam-curing and forms, when the concrete has finally set and hardened, an effective bond between the reinforcing elements and the concrete at the same time serving as an effective rust-protective for the elements, due to, the presence of barium chomate therein, as indicated above.

In the following specific non-limitative examples the application of the invention is described more in detail. The parts in the examples are parts by weight.

and iron or steel reinforcing elements are dipped therein. After drying of the coating the elements are cast into common concrete, consisting of Portland cement, sand, gravel and water.

Example 2 Iron or steel reinforcing rods are treated with a mixture of Parts Water-glass solution (common market product) 100 Barium chromate 50 When the coating has been dried, the rodsare cast into 4 a foam-concrete prepared from slag cement, fine sand, water and a foaming agent.

Exainple 3 A mixture is prepared from Parts Portland cement 100 Barium chromate 20 Casein 6 Water 42 and iron or steel reinforcing elements are dipped therein. When the coating has dried, the elements are cast into a light-weight concrete prepared from Portland cement, ground quartz-containing sand, water and aluminum powder, which light-weight concrete after setting is steamcured in autoclave at an over-pressure of 10 kgs. per

sq. cm.

Example 4 Iron or steel reinforcing elements are coated with a mixture consisting of Parts Finely ground quartz-containing sand 100 Slaked lime 25 Barium chromate 10 .A water-soluble cellulose ether 3 Water 50 After the coating has been dried, the elements are cast into a light-weight concrete mixture consisting of ground, unslaked lime, fly-ash, water and aluminium powder, and

- if desired, 1% gypsum, in a mold. After setting the reinforced concrete bodies are steam-cured 1n autoclave with steam at an over-pressure of 8 kgs.

Example 5 Iron or steam-reinforcing elements are treated with a mixture prepared from When the coating has been dried, the elements are cast into a light-weight concrete prepared from cement, granulated blast furnace slag and water, in a mold, whereupon the setting and hardening of the concrete bodies thus produced is accelerated by exposing the bodies to a moisture-saturated atmosphere at C.

What I claim is:

1. In the making of reinforced concrete and similar structures, wherein rust-proofed steel and iron reinforcing elements are embedded in concrete and similar masses containing small amounts of water-soluble sulfates, the process which comprises coating the reinforcing elements with a liquid grout of a mineral composition containing at least about 1% barium chromate, based on the weight of the solid components of the coating composition and about 2-20% of a hydrophilic organic colloidal binding material which at least swells in water, drying the coating before setting takes place, and surrounding the reinforcing elements with an aqueous slurry of the concrete composition, whereby the coating on the reinforcing elements sets and unites with the concrete during setting thereof, producing effective joints between the reinforcing elements and the concrete, the said barium chromate being adapted to react with the water-soluble sulfates when moisture is present in the surrounding mass to form barium sulfate and chromate ions having a passivating effect on the iron.

2. In the making of reinforced concrete, wherein rustproofed steel and iron reinforcing elements are embedded in concrete containing small amounts of water-soluble sulfates, the process which comprises coating the reinforcing elements with a liquid aqueous grout of Portland cement containing at least about 1% barium chromate, based on the weight of the solid components of the coating composition, and a small proportion of casein sufiicient to render the coating tough and to produce a binding action in the coating, drying the coating before it has had time to set, and embedding the so-coated reinforcing elements in a slurry of a hydraulic cement and steamcuring the cement, whereby a reinforced concrete is produced with effective joints between the reinforcing elements and the concrete, the said barium chromate being adapted to react with the water-soluble sulfates when moisture is present in the surrounding mass to form barium sulfate and chromate ions having a passivating effect on the iron.

3. In the making of reinforced steam-cured 1ight-weight concrete, wherein rust-proofed steel and iron reinforcing elements are embedded in concrete containing small amounts of water-soluble sulfates, the process which comprises coating the reinforcing elements with a liquid aqueous grout of Portland cement containing at least about 1% barium chromate, based on the weight of the solid components in the coating composition, and a small proportion of a hydrophilic organic colloidal binding material sufficient to render the coating tough and to produce a binding action in the coating, drying the coating before it has had time to set, and embedding the so-coated reinforcing elements in a slurry of Portland cement containing a gas-producing agent in an amount suflicient to produce a porous concrete, and subjecting the whole to a curing by pressure-steam, whereby a reinforced porous steam-cured light-weight concrete is pro duced with effective joints between the reinforcing elements and the concrete, the said barium chromate being adapted to react with the water-soluble sulfates when moisture is present in the surrounding mass to form barium sulfate and chromate ions having a passivating effect on the iron.

4. The process of claim 3 wherein the liquid aqueous grout comprises approximately the following: parts of Portland cement, 20 parts barium chromate, 6 parts casein, and 42 parts water, and the embedding slurry comprises approximately the following: Portland cement, ground quartz-containing sand, aluminum powder and water, and wherein the coated reinforcing elements and slurry, after setting, are steam cured at a pressure of 10 kgs. per sq. cm.

References Cited in the file of this patent UNITED STATES PATENTS 96,936 Mariner et a1 Nov. 16, 1869 2,105,324 Huttemann et a1 Ian. 11, 1938 2,374,562 Owens Apr. 24, 1945 2,416,064 Patterson et a1 Feb. 18, 1947 2,430,589 Sloan Nov. 11, 1947 2,591,625 Simonsson Apr. 1, 1952 2,611,945 Simonsson Sept. 30, 1952 2,668,122 Pitrot Feb. 2, 1954