JPH0228532B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to certain concrete compositions which are expected to substantially completely inhibit corrosion of metal parts contained therein for a sustained period of time. Concerning concrete compositions discovered without. The present invention relates to corrosion inhibited concrete compositions containing high strength concrete produced from hydraulic cement, the concrete compositions containing at least about 2 percent calcium nitrite therein. BACKGROUND OF THE INVENTION Concrete produced from hydraulic cements, most commonly Portland cement, is used as a structural component in a variety of applications, such as roads, bridges, buildings, high-rise car parks, etc. In order to enhance the properties of concrete and enable its use in the various applications mentioned above, concrete is commonly used in combination with iron or steel reinforced structural materials encased in the concrete. These reinforced metal materials, usually in the form of metal rods or wires, are exposed to attack by various corrosive elements contained in the concrete as well as by corrosive elements applied externally to the structural material. External corrosive elements include chlorine-containing salts commonly used to remove ice and snow from roads, bridges, trails, etc. Additionally, various structural materials used in coastal buildings are subject to attack by corrosive salts from the surrounding environment. The repair and replacement of structural materials that have deteriorated due to the action of such corrosive forces is extensive, and in some cases requires complete replacement of the structural material as it is no longer suitable for its intended use. In an attempt to counter the corrosive effects commonly encountered in concrete structural materials such as those mentioned above, it has been proposed to use various corrosion inhibitors as additives in the preparation of mixtures. For example, Kano et al.
940, published on February 15, 1950, patent application 1952-33777,
The application, filed on December 27, 1955, discloses the use of sodium nitrite. The patent teaches that sodium nitrite can be added to cement and concrete when mixed to inhibit corrosion of reinforcing iron and steel bars and frames. The aggregate used was sea sand. Dodson et al U.S. Patent No.
No. 3,210,207 teaches the use of a mixture of calcium formate and small amounts of certain nitrites or chromates as corrosion inhibitors for use as promoters in cement. U.S. Pat. No. 3,427,175 to Angstadt et al.
generally discloses the use of calcium nitrite as an accelerator to partially inhibit corrosion in cements. Calcium nitrite may contain small amounts of sodium nitrite and may be used with calcium chloride and other promoters. Whitaker U.S. Patent No.
No. 3,801,338 teaches the use of a mixture of calcium formate and sodium nitrite to add to cement that is to contain metal reinforcement. Improved compressive strength along with sulfuric acid resistance is taught;
It has a "clear corrosion inhibiting effect." As taught by some of the above cited references, the use of sodium nitrite has deleterious weathering effects, promotes alkali-aggregate reactions within the concrete composition, and is therefore a poor corrosion inhibitor. I know something. Several references teach the use of calcium nitrite as an inhibitor when used with any type of cement composition. Calcium nitrite is known to provide only minimal corrosion resistance when used in methods known and described in the prior art. [Problems to be Solved by the Invention] Highly effective corrosion inhibition, i.e., a cement composition capable of substantially completely inhibiting corrosion of metal parts contained therein over a sustained period of time. The need is acutely felt by the construction industry and other industries that use this type of material. [Means and effects for solving the problems] The present invention provides a concrete mixture produced from hydraulic cement, sand, aggregate, and water based on the dry weight of the cement content contained in the concrete mixture. an uncured concrete composition by substantially uniformly mixing with 2 to 5 weight percent calcium nitrite as Produced from hydraulic cement having a cement content of 279 Kg (470 pounds per cubic yard), a water-to-cement ratio of 0.25 to 0.5, and a blend fineness of about 3200 to 5000 cm ² /gm, the concrete composition After at least 351Kg/ ^cm2 (5000psi)
a reinforced concrete structure characterized in that metal parts are placed in the uncured concrete composition and the composition is cured while producing a shaped structure. A method for substantially completely inhibiting corrosion of metal parts is provided. Furthermore, the present invention provides that the concrete mixture contains 2 to 5 ml of water based on the dry weight of hydraulic cement, sand, aggregate, water, and cement content of the concrete mixture.
% calcium nitrite and the concrete mixture contains 50 to 90 percent complex silicate content, at least 279 kg per cubic meter of concrete (470 lbs per cubic yard)
, a water-to-cement ratio of 0.25 to 0.5 and a blend fineness of 3200 to 5000 cm ² /gm, the mixture having a cement content of at least 351 Kg / cm ² (5000 psi) after curing for 28 days. A reinforced concrete structure produced from a high-strength concrete mixture loaded with metal parts characterized by its ability to exhibit compressive strength is provided. The cement component in this concrete is a hydraulic cement, such as Portland cement. These cements are commonly known and are manufactured by calcining a mixture of limestone and clay to form clinker, which is then ground to a fine powder. The main compounds found in Portland cement are tricalcium silicate,
These are dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. Tricalcium and dicalcium silicates are believed to be the major binding components in Portland cement. Tricalcium silicate, when mixed with water, forms calcium silicate hydrate and calcium hydroxide, known as tobermoriete gel. Dicalcium silicates produce similar main products when contacted with water, but the reaction rate is much lower. The tricalcium silicate, which has a greater reaction rate, determines most of the hardening rate of the cement. It is known that Portland cements are commercially available with a range of setting rates to provide materials suitable for different applications. Four general types of Portland cement are commonly produced which vary primarily in the relative amounts of tricalcium silicate and dicalcium silicate present in the cement. The percentages of the main compounds present in each type of cement are shown in Table 1.

[Table] Concrete products encounter various corrosive environments. In some cases it is an inherent part of this environmental concrete, for example by the use of calcium chloride promoters or by the use of chloride-containing materials or chloride-containing water. Other environments may be foreign, such as through the use of calcium chloride and/or salt in snow and ice removal, salt spray or exposure to salt water. Such environments tend to attack and corrode metal parts within or in contact with concrete. The present invention provides compositions and methods for inhibiting such corrosion. Important factors believed to substantially contribute to the unexpected result of achieving substantially complete corrosion inhibition of metal components contained in concrete over a sustained period of time are as follows: A high-strength concrete composition capable of achieving a compressive strength of at least 351 Kg/cm ² (5000 psi) after days in combination with calcium nitrite used at 2 to 5 percent by weight based on the weight of the dry concrete composition. It is to be. The present invention relates specifically to concrete compositions and not to cement pastes or mortar mixtures. The cement paste consists of hydraulic cement and water, and the mortar mixture consists of hydraulic cement, sand and water. These materials do not exhibit the high strength and related properties required by the compositions described herein. The composition of the present invention provides at least 351 Kg/cm ² after 28 days as determined by standard tests in the art.
(5000psi) requires the use of concrete compositions capable of exhibiting high compressive strength (e.g.
(see ASTM). Concrete is a dry mixture of hydraulic cement, sand and aggregate that is mixed with water to cause immediate hydration. The high strength required for concrete compositions is
For example: (a) the ratio of water to hydraulic cement used in concrete production; (b) the cement content or factors; (c) the composition of the hydraulic cement, in particular the silicate content therein; (d) the hydraulic cement used. (e) by varying the particle size and distribution of the aggregate used, or a combination of these methods. The high strength concrete compositions required by this invention can be produced by using a water to cement ratio as low as achievable while still allowing mixing of the ingredients. Water to cement ratio is 0.25
It should be ~0.5, preferably 0.25-0.45.
This ratio can be reduced without loss of mixing capacity by using conventional Water reducing agents and/or super plasticizers in methods and amounts well known to those skilled in the art. The concrete has a high cement content or factor, i.e. at least 279 Kg per cubic meter of concrete (at least about 5 to 9 bags (standard 94 lb.) per cubic yard of concrete, preferably about 6 to 9 bags per cubic yard of concrete). Should. Suitable cement compositions are hydraulic cements containing high silicate components. The content of silicate components in the form of tricalcium silicate (C ₃ S) and dicalcium silicate (C ₂ S) is approximately 50-90
percent, preferably about 65-90 percent. Another factor contributing to the high strength of the resulting concrete composition required by the present invention is the fineness of the particle size of the cement used. Cement is approx.
It should have a Blaine fineness of 3200-5000, preferably 3200-4000 cm ² /g. Sand and aggregate is an American Concrete Institute (ACI) publication.
211 should be met.
High strength due to the use of maximum amounts of large aggregates and sand particles that approach the grain size of the cement, where the size of the aggregate is graded to achieve virtually complete elimination of voids within the final concrete product Concrete is obtained. The mixture should be substantially homogeneous and consolidated. Calcium nitrite, when used in certain amounts in combination with the concrete described above, produces a composition that virtually eliminates, although unexpectedly, corrosion to metal parts contained in the concrete components. , thus extending the life of concrete products produced from such compositions and eliminating the need for repairs. The amount of calcium nitrite required is at least 2 to 3 weight percent based on the weight of the concrete composition. Higher amounts can be used if economically possible. Amounts in excess of 5 weight percent are considered unnecessary. Calcium nitrite can be added to concrete by various techniques. Calcium nitrite can be added to the cement clinker before grinding and can be thoroughly mixed with the cement components during the grinding process. Calcium nitrite can also be added to the dry concrete mix and mixed thoroughly to evenly disperse the calcium nitrite throughout the dry concrete. Calcium nitrite can be dissolved in the water used to produce concrete compositions. The concrete mixture can be premixed with water and then mixed or contacted with calcium nitrite. Generally, any mixing method that allows the calcium nitrite to be substantially uniformly mixed with the concrete mixture prior to forming the hardened composition may be used. Other conventional admixtures can be added to the composition in methods and amounts commonly known in the art. Such admixtures include, for example, water reducing agents such as calcium lignosulfonates, glucose polymers, polysaccharides, or superplasticizers such as polynaphthalenesulfonates, polymelamine formaldehyde sulfonates. Other conventional agents may be used in a known manner to the extent that they contribute to the superior properties of the resulting concrete and do not reduce the required compressive strength mentioned above. EXAMPLES The following examples are given for illustrative purposes only and are not meant to limit the invention other than as in the claims set forth herein. All parts and percentages are by weight unless otherwise indicated. Example 1 A ready mix supplier with a cement factor of 334 Kg per cubic meter (6 bags per cubic yard) using type I cement (composite silicate ratio 77%, blend fineness approximately 3500 cm ² /g) Concrete (maximum aggregate diameter 1″ (2.54cm)) manufactured by ―mix supplier) is mixed with 2% calcium nitrite by weight of cement.
10.2 cm (4 inches) slump, 4.8%
concrete (water ^/ cement ratio 0.46) with an air content of 2.54cm (1 inch) from the surface of large bloom finished concrete
Cast into a 183 cm x 61 cm (6 ft x 2 ft), 15.2 cm (6 in) thick mold containing a double mat of reinforcing rod (5/8" diameter) at the bottom. After 7 days of casting, the slab was covered with burlap and plastic and kept damp, then the mold was removed and the slab was placed 91.5 cm above the ground.
placed on piers (3 feet) apart. During the next 5 weeks a dam was installed on the top surface and at the beginning of the 7th week, 3% sodium chloride solution (1200 milliliters) was sprinkled on the surface daily. ACI Publication SP-49 (ACI Publication SP-
49), pp. 71-82 (1975); California Transportation Laboratory Research Report
Laboratory Research Report）CA―DOT―
TL-5116-12-75-03, January 1975; and U-hlig, Corrosion & Corrosion Control, p. 45 (1971)
The open circuit potential was measured frequently according to the method described in . After approximately 6 months, no areas involved in corrosion (with a potential more negative than -0.350 volts with respect to the copper-copper sulfate (CCS) reference electrode) were present on the calcium nitrite-containing deck; The concrete has a slump of 11.1cm (4 3/8″), an air content of 5.5% and 316Kg/cm ² after 28 days.
(blank) made from the same composition without calcium nitrite, with a strength of (4500 psi)
Above, 36.4% of the total area was involved in corrosion. Example 2 For comparison, aggregate with a maximum diameter of 1.59 cm (3/8"), Type I, 334 Kg per cubic meter (6 bags per cubic yard) in a 0.283 cubic meter (10 cubic foot) mixer. Cement (composite silicate ratio
77%, Blen fineness approx. 3500cm ² /g), 0.56 water /
Cement ratio, 8.25cm (3 1/4″) slump, 4.6
% air and 2% calcium nitrite with a 28 day compressive strength of 317 Kg/cm ² (4515 psi). After approximately 6 months, this concrete was cast into slabs using the same method as described in Example 1.
% was involved in corrosion, but the control material (no calcium nitrite, water/cement ratio of 0.57, 12.1 cm (4
3/4″) slump, 4.5% air, 253Kg/cm ²
Compressive strength after 28 days (3595psi) was 100% related to corrosion. Calcium nitrite showed some effectiveness in inhibiting corrosion as measured by the same method as described in Example 1 above. −0.500V and − for CCS electrode
The area with open circuit potential between 0.55V is 0.3% for slabs containing calcium nitrite;
For decks that do not have calcium nitrite
It was 7.4%. −0.450V and − for CCS electrode
The area recorded between 0.500V was 9.4% for slabs with calcium nitrite and 18.5% for slabs without calcium nitrite. Nevertheless, the corrosion inhibition effect in this series was not substantially the same as described in Example 1. Example 3 Again, for comparison, a low strength concrete composition made in substantially the same manner as described in Example 2 above gave the following parameters.

Table: Although the use of calcium nitrite reduced corrosion, unexpected virtually complete inhibition was not achieved. Example 4 Concrete made essentially as in Example 2 but with 3 fluid ounces of a calcium lignosulfate-based water reducer gave the following parameters.

[Table] Area, %
One month of testing is roughly equivalent to one year of Kansas winter. It can be seen that both the control sample and the calcium nitrite-containing sample exhibit high compressive strength, but only the calcium nitrite-containing sample shows virtually no corrosion after a sustained period of time. Example 5 Slabs measuring 6 feet x 2 feet x 6 inches were made using the following five series of concrete mixes. In each series, type I cement (composite silicate ratio 77%,
Blen fineness of approximately 3500 cm ² /g) was used. These slabs were subjected to an accelerated corrosion test developed by Federal Highway Headquarters.

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[Table] ^cm2
(psi 4695 4900 5270)

[Table] Su company's water reducing agent

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[Table] The slab was formed in a wooden formwork. from the bottom of the formwork
Two grid-shaped reinforcing bars were placed at 1 inch and 5 inches. The reinforcing rods were therefore located one inch from the top and bottom surfaces of the molded slab. The reinforcing rod is commercially available. The slabs were molded according to the Federal Highway Headquarters design, bloomed on top, and allowed to cure for one week before being removed from the mold. The slab was placed on concrete block piers to lift it off the ground (approximately 102 cm (approximately 40 inches)). The slab was leveled, a dam was placed around the outer 5.1 cm (2 inches) from the top, and 1200 ml of a 3% NaCl solution was injected daily starting 6 weeks after casting. Overlay the grid on each slab, 5.1 cm/5.1 cm (2
It was divided into 9 x 33 = 297 squares (inch x 2 inches). Before measuring the open circuit potential on each slab, the salt solution was wiped off, rinsed with water, and dried with a sponge. In 15 minutes to 1 hour, depending on wind and temperature conditions, the slab dried to the extent that the concrete was still wet but had no water sheen.
A commercially available copper-copper sulfate reference electrode was connected to a Weston Model 600 Autoranging Digital Voltmeter.
Voltmeter) and connected to the reinforcing rods by electrical wires installed before concrete pouring. The potential was measured for each square of the slab divided by the grid. It has been established that an increase in the value of the negative potential measured indicates an increase in corrosion, and the value of the negative potential
It has also been found that less than 350 mV shows virtually no corrosion. Figure 1 shows the distribution of the measured potential for each series for a concrete mixture that does not contain calcium nitrite, and Figure 2 shows the distribution of the measured potential for each series for a concrete mixture with a calcium nitrite content of 2%. . According to FIG. 1, all samples without calcium nitrite show a substantial amount of corrosion (above the -350 mV line). Also, from Figure 2, the calcium nitrite content is 2% and the strength is 351Kg/cm ²
(5000psi) or higher samples (series,,) are the only ones showing no corrosion (below the -350mV line)
I understand. Figures 3 and 4 show the corrosion rate determined from the distribution of the measured potential, and Figure 3 shows the corrosion rate determined from the distribution of the measured potential.
Measurement data after 36 months (this corresponds to about 40 years of severe winters) was used, and Figure 4 uses measurement data after 12 months (this corresponds to about 13 years) of salt treatment. Figures 3 and 4 show that even after long tests such as those described above, calcium nitrite contents of 2% or 3% result in very little corrosion. [Effects of the Invention] As described above, according to the present invention, corrosion of reinforcing metals in concrete structures is significantly suppressed beyond prediction. It has been found that corrosion of the reinforcing metal by corrosive elements contained in concrete as well as by corrosive elements from the outside is substantially completely suppressed over a long period of time.

[Brief explanation of drawings]

Figure 1 is a graph showing the distribution of potentials measured in an accelerated corrosion test for a concrete mixture that does not contain calcium nitrite, and Figure 2 is a graph showing the distribution of potentials measured in an accelerated corrosion test for a concrete mixture with a calcium nitrite content of 2%. Fig. 3 is a graph showing the corrosion rate determined from the distribution of the measured potential after 36 months of the accelerated test, and Fig. 4 is a graph showing the corrosion rate determined from the distribution of the measured potential after 12 months of the accelerated test. It is a graph showing the ratio of

Claims (1)

[Claims] 1. A concrete mixture made from hydraulic cement, sand, aggregate and water is treated with 2 to 5 weight percent nitrous acid based on the dry weight of the cement content contained in the concrete mixture. substantially uniformly mixed with calcium to produce an uncured concrete composition, the uncured concrete composition having a composite silicate ratio of 50 to 90 percent, at least per cubic meter of concrete.
Cement content of 279Kg (470 lbs per cubic yard), water to cement ratio of 0.25-0.5 and approx.
Produced from hydraulic cement having a blend fineness of 3200 to 5000 cm ² /gm, the concrete composition can exhibit a compressive strength of at least 351 Kg/cm ² (5000 psi) after 28 days and during the production of shaped structures. A method for substantially completely inhibiting corrosion of metal parts placed in a reinforced concrete structure, comprising placing the metal parts in the uncured concrete composition and curing the composition. 2. The method according to claim 1, wherein the uncured concrete composition contains a superplasticizer. 3. The method of claim 1, wherein the uncured concrete composition contains a moisture reducing agent. 4 The concrete mixture contains hydraulic cement, sand,
Produced from 2 to 5 percent calcium nitrite based on the dry weight of aggregate, water and cement content of the concrete mixture, the concrete mixture containing 50 to 90 percent complex silicate content, at least per cubic meter of concrete.
Cement content of 279Kg (470 lbs per cubic yard), water to cement ratio of 0.25-0.5 and 3200
produced from a hydraulic cement having a blend fineness of ~5000 cm ² /gm, the mixture containing metal parts characterized in that it can exhibit a compressive strength of at least 351 Kg/cm ² (5000 psi) after curing for 28 days. Reinforced concrete structures produced from high strength concrete mixtures. 5. The structure of claim 4 further comprising a superplasticizer therein. 6. The structure of claim 4 further comprising a moisture reducing agent therein.