DE2152312B2 - Corrosion protection agent for steel reinforcement in steam-hardened concrete - Google Patents

Description

prevents the formation of calcium silicates during the superheated steam treatment, so that the coating remains high even after steam curing Retains alkalinity and ensures passivation of the reinforcing steel.

[mV]

This fact is supported by experimental results based on electrochemical Trials for the different compositions of the coatings were obtained. In the following graphic representation

50 60 70 80 90 100 UO 120

1200 -

1600

Anodic polarization of reinforcing steel

738 - steel without coating,

739 - steel with coating according to DT-PS 8 48 923
882 - steel with coating according to the invention.

the polarization curves of reinforcing steel are shown, which are under the influence of the different Coatings.

All test pieces were made from cellular concrete with a specific weight of 700 to 800 kg / m ³ . From curve 882 (bitumen coating according to the invention) it can be seen that the reinforcing steel under the coating is completely passivated. Curve 739 (coating of calcium silicates with an organic binder, the influence of which was eliminated in the course of the autoclave treatment, made from lime, quartz sand and casein glue according to DT-PS 8 48 923) shows that the reinforcing steel is in an activated state. Finally, curve 738 has been recorded from a fitting steel without an anti-corrosion coating.

The agent receives its advantageous properties (increased adhesiveness and corrosion resistance) mainly through the autoclave treatment of reinforced concrete parts under steam pressure between 8 and 12atü.

The ohmic resistance of the coating according to the invention after 28 hours of storage in water is 10 ₇ ohm cm, whereas in the case of the calcium silicate coating according to DT-PS 8 48 923 the ohmic resistance practically does not exceed the resistance of the concrete itself.

The high density of the coating according to the invention and the associated impermeability to moisture and gas is a factor that, in turn, also enhances the high anti-corrosion properties of the Coating ensures and also prevents the lime from the action of carbon dioxide the air is carbonized, which in turn increases the alkalinity of the coating and the passivation of the reinforcing steel can be guaranteed.

The corrosion resistance properties of the coating were proven by corrosion tests determining the suitability coefficient K of the protective coating. K represents the ratio of the rate of corrosion of reinforcing steel without a coating to the rate of corrosion of armature steel with a coating. The rate of corrosion is measured by the weight loss of the metal per unit surface area and unit time.

If casein, gelatine or cellulose ether are used as the organic binder, the protection coefficient for the corresponding coatings, as produced in accordance with DT-PS 8 42 468 and 8 48 923, is K = 5 to 7 and usually not more than 10.

The protection coefficient for a bitumen coating of the type according to the invention with optimal parameters, on the other hand, amounts to K - 1500, when using petroleum bitumen of the optimal type with a softening point of 90 ° C. The final size of the coefficient could practically not be determined by the following three quick determinations:

a) alternately wetting with 3% saline solution for one hour and drying at 6O ⁰ C for 23 hours,

b) alternating wetting with water for 7 hours and drying for 17 hours 60 ° C,

c) alternating wetting with water and drying at 40 to 45 ° C in eight cycles per day (so-called Gardner wheel).

In tests in the humid chamber at a relative humidity of 95% and a temperature of 25 to 50 ^° C., no signs of corrosion were observed under the coating according to the invention after seven years of testing, so that the coefficient K could not be determined under these conditions; the experiments are being continued into the present day.

When using petroleum bitumen with a softening point of 70 ⁰ C in the inventive coating, the protective properties were somewhat lower; a value for K of 1500 was obtained.

When producing the bitumen coating in the composition according to the invention, but with the difference that, according to the teaching of DT-AS 1119 731, slaked lime is used instead of unslaked lime, one obtains a protection coefficient that is 30 times lower, and the adhesion of the coating to the Reinforcement and the concrete is lowered by two to three times. In the case of the coating according to the invention, the adhesiveness is in the range of 20 to 30 kg / cm ² for smooth reinforcement, while the adhesion of unprotected reinforcement is around 15 kg / cm ² and even 12 to 13 kg when using slaked lime / cm ² decreased.

A further reduction in the protective and mechanical properties of the coating occurs if you know how also proposed in DT-AS 1119 731, an organic solvent is used. this happens according to a sharp decrease in the density of the coating due to pore formation during the Drying when the solvent evaporates.

The anti-corrosion agent according to the invention for the reinforcement is produced in the following manner.

Bitumen is melted in a heated bath equipped with mechanical screw stirrers, whereupon the lime-sand mixture is poured into the melt as an additive while stirring. The mixture mentioned is produced by previously grinding together unslaked lime and quartz sand. The grinding fineness of the mixture is determined according to the specific sand surface and should be between 1000 and 3000 cm ² / g. The active calcium oxide content in the mixture can be 9 to 30%.

After the aggregate has been introduced into the bitumen, the temperature of the mixture produced is increased to 150 to 170 ^° C. Then the reinforcement (steel baskets, nets or individual bars) is immersed in the hot mixture at the temperature mentioned and it is held for a few minutes in it and take it out. The holding time of the reinforcement in the hot mixture depends on the diameter of the reinforcement and the desired thickness of the covering on the metal: the longer the holding time of the reinforcement in the mixture, the thinner the covering will be and vice versa. The working thickness of the covering is between 0.5 and 1 mm, preferably 0.7 mm.

After removing the reinforcement from the bathroom. hold it over the bath for about 1 minute so that the excess mixture drains off. The covering hardens as the reinforcement cools down. At around 20 ^° C., the covering hardens when the reinforcement is transported to the interim storage facility or to the molds. After the pavement has hardened, the reinforcement is ready to be poured in, molded and poured with concrete.

For a better understanding of the invention, the following examples are given for the preparation of the invention Corrosion protection agent for steel reinforcement in autoclave concrete.

example 1

Prepare a means of the following composition:

Oil bitumen

(Softening point 90 ° C) 1 part by weight

Lime-sand mixture with 20%

active calcium oxide 2.5 parts by weight

First the bitumen was melted, after which the lime-sand mixture was added as an aggregate. The latter was previously obtained by grinding together unsoluteed lime and quartz sand. The grinding fineness, determined according to the specific sand surface, was 3000 cm ² / g.

The agent prepared consisting of bitumen and aggregate, the mixture was heated at 150 to 170 ⁰ C, followed by dareintauchte the reinforcement. The diameter of the reinforcing steel is 6 mm. The average holding time of the reinforcement is 2 minutes. After 2 minutes, the reinforcement was removed from the medium and held in the air for 2 minutes. The coating hardened. The thickness of the anti-corrosion coating is 0.7 mm.

The agent was tested through corrosion tests and adhesion tests on concrete and reinforcement examined. The reinforcing steel, which is covered with the agent according to the invention and in cellular concrete

is inserted, no signs had a Korrosionsbeschädigüng, after having been kept in a moist chamber (at relative Lufteuchtigkeit of 95 to 100%, and BTI 25 ± 5 ⁰ C) for 5 years. (According to German standards [DIN 4223], the reinforcing steel inserted in cellular concrete should not have any layer of rust under the corrosion protection coating after a year of testing in a damp room and the corrosion area should not be more than 5% of the total metal surface.)

The adhesive strength of the reinforcement, a smooth, unprofiled bar covered with corrosion protection compound, on the cellular concrete was 32 kp / cm ² with a cellular concrete density of 800 kg / m ³ (the adhesive strength of the unprotected reinforcement on the specified concrete is 14 kp / cm ² ) .

Example 2

Prepare a means of the following composition:

oil bitumen

(Softening point 90 ^° C.) .... 1 part by weight

Lime-sand mixture with 20%

active calcium oxide 2.5 parts by weight

Unslaked lime and quartz sand were ground together in the ball mill up to a specific sand surface of 1000 cm ² / g. The subsequent operations in the manufacture of the agent, whose

Application to a steel reinforcement and the test lime-sand mixture with 9%

Test conditions correspond to the active calcium oxide in Example 1, 2.5 parts by weight

described.

The adhesive strength of the anti-corrosion compound The joint grinding of quartz sand and

occupied reinforcement on cellular concrete is 24.5 kg / cm ² , s unslaked lime was up in a ball mill

After 4 years of testing, the reinforcement stayed in the specific quartz sand surface of 1000 cm ² / g

no corrosion damage was carried out in a damp room. The subsequent operations at

to be recognized by the metal under the covering. the preparation of the agent, its application on

. -Ii a steel reinforcement and the test experimental conditions

Examples _lo correspond to those described in Example 1. the

A means of the following cohesive strength is prepared with this anti-corrosion agent

Settlement: occupied reinforcement on cellular concrete is 12.7 kp / ctn *.

oil bitumen ^ ^first ** ^eK * ⁱⁿ corrosion damage (3% of metal

(Softening point 90 ⁰ C) .... 0.5 parts by weight total area) on the reinforcement was after 2

Olbitumen 15 search years in a damp room recognizable

(Softening point 70 ° C) 0.5 parts by weight ^bar

Lime-sand mixture with 20% Example 6

active calcium oxide 2.2 parts by weight *, · »♦ ·»>, · ,. 1 t 1 α -y

One prepares a means of the following

Unquashed egg lime and quartz sand were in a 20 settlement:
Ball mill up to the specific sand surface of

Grind together 2000 cm * / g. The subsequent oil bitumen

Operations in the production of the agent, the (softening point 90 ⁰ C) 1 part by weight

Application to a steel reinforcement and the test lime-sand mixture with 30%

Search conditions correspond to the active calcium oxide in Example 1, 2 parts by weight

wrote.

The adhesion strength of the corrosion protective composition The joint grinding of quartz sand and occupied reinforcement at the cellular concrete is 18.8 kgf / cm ² quicklime was in a ball mill and 36.9 kgf / cm ² at the sealing concrete which a raw for specific sand surface 3000 cm ^z / g has a density of 1900 kg / m ³ . After 4 years of trial 30 performed. The subsequent work steps in the reinforcement in a damp room were not the production of the agent, its application to a corrosion damage to the metal under the covering to steel reinforcement and the test conditions recognize. correspond to those described in Example 1. The " . . ,. Adhesion strength of the with this anti-corrosion agent

35 occupied reinforcement on the cellular concrete is 14 kp / cm ² .

A remedy is prepared as follows- The first source of corrosion damage (2% of the

Settlement: total metal area) on the reinforcement was after

Oil damage ^ Years of experimentation in a damp room

(Softening point 90 ^° C.) .... 1 part by weight recognizable.

Lime-sand mixture with 20% * ° Example 7

active calcium oxide 2 parts by weight. ., .. ,,,,.,

^J One rescues the following means of

Unslaked lime and quartz sand were in a settlement:
Ball mill up to the specific sand surface of
Grind together 3000 cm * / g. The subsequent 45 oil bitumen

Operations in the production of the agent, the (softening point 90 ⁰ C) 1 part by weight

Application to a steel reinforcement and the test lime-sand mixture with 20%

Test conditions corresponding to the active calcium oxide in Example 1, 1.66 parts by weight

described.

The adhesive strength of the anti-corrosion compound 5 ° The joint grinding of quartz sand and

occupied reinforcement on cellular concrete is 32 kp / cm *. Quick lime was put up in a ball mill

After 4 years of testing, the reinforcement had been in a wet room with a specific sand surface of 2000 cm ² / kg, and no corrosion damage had occurred. The subsequent operations be

Recognizable by the metal under the protective covering. the production of the agent, the application of which au!

. 55 a steel reinforcement and the test test condition i

Example 5 correspond to those described in Example 1.

A means is prepared as follows: The adhesive strength of this corrosion protection

Settlement: medium occupied reinforcement on cellular concrete is 12.8 kp

cm*. After 4 years of trials, the armament

Shale bitumen 60 in a damp room did not show any corrosion damage

(Softening point 72 ° C) 1 part by weight can be seen on the metal under the protective covering.

Claims (3)

Steam curing the presence of the organic binder does not affect the process of curing the cement in the coating, so that the final properties of the coating, such as corrosion 1. Corrosion protection agent made from bitumen and strength, water resistance, mechanical strength aggregate for steel reinforcement in steam etc. not hardened by the properties hardened concrete, characterized by this distinguish cement. η et that it is an aggregate from undeleted From the DT-PS 8 48 923 coatings are known, Lime and quartz sand consisting of a lime-sand mixture of lime and a mixture containing silicon dioxide contains io terial that exist under the conditions of 2. Corrosion protection agent according to claim 1, steam curing to convert to calcium silicates. Besides characterized in that it contains 1 part by weight of the coating organic binders Bitumen and 1 "5 to 2.5 parts by weight of lime- Prevents the coating from flaking off before Sand mix with 9 to 30% active calcium - inserting the reinforcements in molds; the bulk oxide consists. 15 ratios are chosen so that the influence of the 3. Corrosion protection agent according to claim 1, da- organic binder on the coating by the characterized in that it is repealed or made dispensable from 1 part by weight of steam curing Bitumen and 2.5 parts by weight of lime-sand-Ge and the formation of calcium silicates do not mix with 20% active calcium oxide. is hindered from which, according to the teaching of this 20 patent specification the coating should only exist. The formation of calcium silicates from sand and Lime, however, is a factor in terms of the anti-corrosive effect of the coating to be achieved undesirable process because in this way the 25 Alkalinity of the lime-sand mixture from the pH value 12.5, with a passivation of the reinforcing steel it is ensured that the pH value is lowered, which is significantly below the critical pH value (Order of magnitude 11), in which the upper The invention relates to the anti-corrosion surface of the reinforcing steel in the active state The agent for steel reinforcement turns into steam-hardened, which promotes the corrosion process. Concrete, hereinafter referred to as autoclave concrete. The layer of calcium silicate that lies beneath the The anti-corrosion agents are suitable for the influence of the water vapor formed is for protection against moisture the reinforcement with reinforced construction contours and atmospheric oxygen sufficiently permeable Etructions. The corrosion protection with the help of 35 and does not represent a major obstacle to the process The means mentioned is necessary because it is in contrast to the corrosion processes. to sealed reinforced concrete structures of the autoclave - From the DT-AS 1119 731 coatings are known, Concrete, especially cellular concrete, because of reduced exposure to organic solvents (hydrocarbon alkalinity and increased air, gas and moisture) dissolved bitumen or dissolved synthetic permeability the reinforcement against corrosion not 40 resins with a content of highly dispersed hydroxides protects. of alkaline earths from breath weight 24.3 to 137.5 Corrosion protection agents for steel are known. As explained below, leads reinforcements in autoclave concrete, preferably in cells, but the use of slaked lime is not permitted concrete made from shale bitumen and portland cement of the desired increase in protective and mechaals Aggregate exist (USSR copyright 45 niche properties of the coating during the No. 1 560 090). Autoclave treatment. The known agents have too little adhesion. The object of the invention is to determine the type of aggregate ability on the reinforcement and on the concrete mentioned, on average, that of bitumen and aggregate on what is a significant reduction in strength and for corrosion protection of the steel reinforcement structures, in particular of bending cone 50 in autoclave concrete is used to change in such a way that result in instructions. achieves good adhesion to the reinforcement Furthermore, from DT-PS 8 42 468 an anti-corrosion and the formation of calcium silicate is prevented, sion coating for steel reinforcement known, the object of the invention is there- Cement or cement, lime and sand as well as one solved by the fact that the agent as an additive consists of an organic binding agent of preferably colloidal, lime-sand mixture, consisting of unslaked glue-like character. In contrast to lime and quartz sand, contains
the previously more common anti-corrosion coatings. Preference is given to an agent consisting of 1 part by weight based on cement and glue, bitumen and 1.5 to 2.5 parts by weight, preferably consolidation after your application under atmospheric 2.5 parts by weight, lime-sand mixture with a Conditions takes place, one saw the following content of active calcium oxide between 9 and 30%, parts: the organic binder will be in one of the - preferably 20%. like ratio used that the possibility The agent according to the invention has an increased the peeling or crumbling of the coating adherence to the reinforcement and to the autoclave from the surface to be protected, in particular from concrete of various types, including cellular concrete, reinforcement, before being placed in molds and 65 and high corrosion resistance,
the subsequent shaping of the reinforced concrete. The bitumen, which is in the lime-sand mixture in the Certificates is excluded, and that on the other hand, proportions used according to the invention are introduced in the further consolidation of the concrete before it has been, without the use of solvents